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TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. THE LOX LANGUAGE · CRAFTING INTERPRETERS A static type system is a ton of work to learn and implement. Skipping it gives you a simpler language and a shorter book. We’ll get our interpreter up and executing bits of code sooner if we defer our type checking to runtime. After all, the two languages we’ll be using to implement Lox are both statically typed. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more CONTROL FLOW · CRAFTING INTERPRETERS The semicolons in the rules aren’t quoted, which means they are part of the grammar metasyntax, not Lox’s syntax. A block does not have a ; at the end and an if statement doesn’t either, unless the then or else statement happens to be one that ends in a semicolon.. An if statement has an expression for the condition, then a statement to execute if the condition is truthy. A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS Don’t worry, I won’t spam you.) Our Java interpreter, jlox, taught us many of the fundamentals of programming languages, but we still have much to learn. First, if you run any interesting Lox programs in jlox, you’ll discover it’s achingly slow. The style of interpretation it uses — walking the AST directly — is good enoughfor some
GARBAGE COLLECTION · CRAFTING INTERPRETERS Throughput is the total fraction of time spent running user code versus doing garbage collection work. Say you run a clox program for ten seconds and it spends a second of that inside collectGarbage (). That means the throughput is 90% — it spent 90% of the time running the program and 10% on GC overhead. CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE Crafting Interpreters. A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up withnew
TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. THE LOX LANGUAGE · CRAFTING INTERPRETERS A static type system is a ton of work to learn and implement. Skipping it gives you a simpler language and a shorter book. We’ll get our interpreter up and executing bits of code sooner if we defer our type checking to runtime. After all, the two languages we’ll be using to implement Lox are both statically typed. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more CONTROL FLOW · CRAFTING INTERPRETERS The semicolons in the rules aren’t quoted, which means they are part of the grammar metasyntax, not Lox’s syntax. A block does not have a ; at the end and an if statement doesn’t either, unless the then or else statement happens to be one that ends in a semicolon.. An if statement has an expression for the condition, then a statement to execute if the condition is truthy. A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS Don’t worry, I won’t spam you.) Our Java interpreter, jlox, taught us many of the fundamentals of programming languages, but we still have much to learn. First, if you run any interesting Lox programs in jlox, you’ll discover it’s achingly slow. The style of interpretation it uses — walking the AST directly — is good enoughfor some
GARBAGE COLLECTION · CRAFTING INTERPRETERS Throughput is the total fraction of time spent running user code versus doing garbage collection work. Say you run a clox program for ten seconds and it spends a second of that inside collectGarbage (). That means the throughput is 90% — it spent 90% of the time running the program and 10% on GC overhead. INTRODUCTION · CRAFTING INTERPRETERS In these pages, we will walk step-by-step through two complete interpreters for a full-featured language. I assume this is your first foray into languages, so I’ll cover each concept and line of code you need to build a complete, usable, fast language implementation. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored APPENDIX I · CRAFTING INTERPRETERS Note that block is a statement rule, but is also used as a nonterminal in a couple of other rules for things like function bodies.. A1 . 1 . 3Expressions. Expressions produce values. Lox has a number of unary and binary operators with different levels of precedence. Some grammars for languages do not directly encode the precedence relationships and specify that elsewhere. GARBAGE COLLECTION · CRAFTING INTERPRETERS Throughput is the total fraction of time spent running user code versus doing garbage collection work. Say you run a clox program for ten seconds and it spends a second of that inside collectGarbage (). That means the throughput is 90% — it spent 90% of the time running the program and 10% on GC overhead. REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more RESOLVING AND BINDING · CRAFTING INTERPRETERS Here, we know that the a being printed is the variable declared on the previous line, and not the global one. Running the program doesn’t — can’t — affect this. The scope rules are part of the static semantics of the language, which is why they’re also called static scope.. I haven’t spelled out those scope rules, but now is the timefor precision:
A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS In less than two thousand lines of clean Java code, we’ll build a complete interpreter for Lox that implements every single feature of the language, exactly as we’ve specified. The first few chapters work front-to-back through the phases of the interpreter — scanning, parsing, and evaluating code. LOCAL VARIABLES · CRAFTING INTERPRETERS Local variables are one of the most-used parts of a language. If locals are slow, everything is slow. So we want a strategy for local variables that’s as efficient as possible. Function parameters are also heavily used. They work like local variables too, so we’ll use the same implementation technique for them. A MAP OF THE TERRITORY · CRAFTING INTERPRETERS You must have a map, no matter how rough. Otherwise you wander all over the place. In The Lord of the Rings I never made anyone go farther than he could on a given day.. J. R. R. Tolkien. We don’t want to wander all over the place, so before we set off, let’s scanthe
CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE Crafting Interpreters. A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up withnew
TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. THE LOX LANGUAGE · CRAFTING INTERPRETERS A static type system is a ton of work to learn and implement. Skipping it gives you a simpler language and a shorter book. We’ll get our interpreter up and executing bits of code sooner if we defer our type checking to runtime. After all, the two languages we’ll be using to implement Lox are both statically typed. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more CONTROL FLOW · CRAFTING INTERPRETERS The semicolons in the rules aren’t quoted, which means they are part of the grammar metasyntax, not Lox’s syntax. A block does not have a ; at the end and an if statement doesn’t either, unless the then or else statement happens to be one that ends in a semicolon.. An if statement has an expression for the condition, then a statement to execute if the condition is truthy. A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS Don’t worry, I won’t spam you.) Our Java interpreter, jlox, taught us many of the fundamentals of programming languages, but we still have much to learn. First, if you run any interesting Lox programs in jlox, you’ll discover it’s achingly slow. The style of interpretation it uses — walking the AST directly — is good enoughfor some
GARBAGE COLLECTION · CRAFTING INTERPRETERS Throughput is the total fraction of time spent running user code versus doing garbage collection work. Say you run a clox program for ten seconds and it spends a second of that inside collectGarbage (). That means the throughput is 90% — it spent 90% of the time running the program and 10% on GC overhead. CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE Crafting Interpreters. A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up withnew
TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. THE LOX LANGUAGE · CRAFTING INTERPRETERS A static type system is a ton of work to learn and implement. Skipping it gives you a simpler language and a shorter book. We’ll get our interpreter up and executing bits of code sooner if we defer our type checking to runtime. After all, the two languages we’ll be using to implement Lox are both statically typed. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more CONTROL FLOW · CRAFTING INTERPRETERS The semicolons in the rules aren’t quoted, which means they are part of the grammar metasyntax, not Lox’s syntax. A block does not have a ; at the end and an if statement doesn’t either, unless the then or else statement happens to be one that ends in a semicolon.. An if statement has an expression for the condition, then a statement to execute if the condition is truthy. A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS Don’t worry, I won’t spam you.) Our Java interpreter, jlox, taught us many of the fundamentals of programming languages, but we still have much to learn. First, if you run any interesting Lox programs in jlox, you’ll discover it’s achingly slow. The style of interpretation it uses — walking the AST directly — is good enoughfor some
GARBAGE COLLECTION · CRAFTING INTERPRETERS Throughput is the total fraction of time spent running user code versus doing garbage collection work. Say you run a clox program for ten seconds and it spends a second of that inside collectGarbage (). That means the throughput is 90% — it spent 90% of the time running the program and 10% on GC overhead. INTRODUCTION · CRAFTING INTERPRETERS In these pages, we will walk step-by-step through two complete interpreters for a full-featured language. I assume this is your first foray into languages, so I’ll cover each concept and line of code you need to build a complete, usable, fast language implementation. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored APPENDIX I · CRAFTING INTERPRETERS Note that block is a statement rule, but is also used as a nonterminal in a couple of other rules for things like function bodies.. A1 . 1 . 3Expressions. Expressions produce values. Lox has a number of unary and binary operators with different levels of precedence. Some grammars for languages do not directly encode the precedence relationships and specify that elsewhere. GARBAGE COLLECTION · CRAFTING INTERPRETERS Throughput is the total fraction of time spent running user code versus doing garbage collection work. Say you run a clox program for ten seconds and it spends a second of that inside collectGarbage (). That means the throughput is 90% — it spent 90% of the time running the program and 10% on GC overhead. REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more RESOLVING AND BINDING · CRAFTING INTERPRETERS Here, we know that the a being printed is the variable declared on the previous line, and not the global one. Running the program doesn’t — can’t — affect this. The scope rules are part of the static semantics of the language, which is why they’re also called static scope.. I haven’t spelled out those scope rules, but now is the timefor precision:
A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS In less than two thousand lines of clean Java code, we’ll build a complete interpreter for Lox that implements every single feature of the language, exactly as we’ve specified. The first few chapters work front-to-back through the phases of the interpreter — scanning, parsing, and evaluating code. LOCAL VARIABLES · CRAFTING INTERPRETERS Local variables are one of the most-used parts of a language. If locals are slow, everything is slow. So we want a strategy for local variables that’s as efficient as possible. Function parameters are also heavily used. They work like local variables too, so we’ll use the same implementation technique for them. A MAP OF THE TERRITORY · CRAFTING INTERPRETERS You must have a map, no matter how rough. Otherwise you wander all over the place. In The Lord of the Rings I never made anyone go farther than he could on a given day.. J. R. R. Tolkien. We don’t want to wander all over the place, so before we set off, let’s scanthe
CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scriptinglanguage.
WELCOME · CRAFTING INTERPRETERS This book is a work in progress! ×. If you see a mistake, find something unclear, or have a suggestion, please let me know.To follow its progress, please join the mailing list: FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored INTRODUCTION · CRAFTING INTERPRETERS Fairy tales are more than true: not because they tell us that dragons exist, but because they tell us that dragons can be beaten. G.K. Chesterton by way of Neil Gaiman, Coraline I’m really excited we’re going on this journey together. PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns LOCAL VARIABLES · CRAFTING INTERPRETERS We have a simple, flat array of all locals that are in scope during each point in the compilation process. They are ordered in the array in the order that their declarations appear in the code. Since the instruction operand we’ll use to encode a local is a single byte, our VM has a hard limit on the number of locals that can be in scopeat once.
THE LOX LANGUAGE · CRAFTING INTERPRETERS The subexpressions on either side of the operator are operands.Because there are two of them, these are called binary operators. (It has nothing to do with the ones-and-zeroes use of “binary”.) Because the operator is fixed in the middle of the operands, these are also called infix operators (as opposed to prefix operators where the operator comes before the operands, and postfix where it CONTROL FLOW · CRAFTING INTERPRETERS Logic, like whiskey, loses its beneficial effect when taken in too large quantities. Edward John Moreton Drax Plunkett, Lord Dunsany. Compared to last chapter’s grueling marathon, today is a lighthearted frolic through a daisy meadow. But while the work is easy, the reward is surprisingly large. CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scriptinglanguage.
WELCOME · CRAFTING INTERPRETERS This book is a work in progress! ×. If you see a mistake, find something unclear, or have a suggestion, please let me know.To follow its progress, please join the mailing list: FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored INTRODUCTION · CRAFTING INTERPRETERS Fairy tales are more than true: not because they tell us that dragons exist, but because they tell us that dragons can be beaten. G.K. Chesterton by way of Neil Gaiman, Coraline I’m really excited we’re going on this journey together. PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns LOCAL VARIABLES · CRAFTING INTERPRETERS We have a simple, flat array of all locals that are in scope during each point in the compilation process. They are ordered in the array in the order that their declarations appear in the code. Since the instruction operand we’ll use to encode a local is a single byte, our VM has a hard limit on the number of locals that can be in scopeat once.
THE LOX LANGUAGE · CRAFTING INTERPRETERS The subexpressions on either side of the operator are operands.Because there are two of them, these are called binary operators. (It has nothing to do with the ones-and-zeroes use of “binary”.) Because the operator is fixed in the middle of the operands, these are also called infix operators (as opposed to prefix operators where the operator comes before the operands, and postfix where it CONTROL FLOW · CRAFTING INTERPRETERS Logic, like whiskey, loses its beneficial effect when taken in too large quantities. Edward John Moreton Drax Plunkett, Lord Dunsany. Compared to last chapter’s grueling marathon, today is a lighthearted frolic through a daisy meadow. But while the work is easy, the reward is surprisingly large. OPTIMIZATION · CRAFTING INTERPRETERS The evening’s the best part of the day. You’ve done your day’s work. Now you can put your feet up and enjoy it. Kazuo Ishiguro, The Remains of the Day If I still lived in New Orleans, I’d call this chapter a lagniappe, a little something extra given for free to a customer.You’ve got a whole book and a complete virtual machine already, but I want you to have some more fun hacking on clox. TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter CALLS AND FUNCTIONS · CRAFTING INTERPRETERS We use our friend ALLOCATE_OBJ() to allocate memory and initialize the object’s header so that the VM knows what type of object it is. Instead of passing in arguments to initialize the function like we did with ObjString, we set the function up in a sort of blank state — zero arity, no name, and no code. That will get filled in later after the function is created. SCANNING · CRAFTING INTERPRETERS Take big bites. Anything worth doing is worth overdoing. Robert A. Heinlein, Time Enough for Love The first step in any compiler or interpreter is scanning.The scanner takes in raw source code as a series of characters and groups it into a series of chunks we call tokens.These are the meaningful “words” and “punctuation” that make up the language’s grammar. EVALUATING EXPRESSIONS · CRAFTING INTERPRETERS Given a value of static type Object, we can determine if the runtime value is a number or a string or whatever using Java’s built-in instanceof operator. In other words, the JVM ’s own object representation conveniently gives us everything we need to implement Lox’s built-in types. We’ll have to do a little more work later when we add Lox’s notions of functions, classes, and REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more APPENDIX I · CRAFTING INTERPRETERS Note that block is a statement rule, but is also used as a nonterminal in a couple of other rules for things like function bodies.. A1 . 1 . 3Expressions. Expressions produce values. Lox has a number of unary and binary operators with different levels of precedence. Some grammars for languages do not directly encode the precedence relationships and specify that elsewhere. STRINGS · CRAFTING INTERPRETERS This takes a bare Obj pointer and wraps it in a full Value. 19 . 2Struct Inheritance. Every heap-allocated value is an Obj, but Objs are not all the same. For strings, we need the array of characters. A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS This book is a work in progress! ×. If you see a mistake, find something unclear, or have a suggestion, please let me know.To follow its progress, please join the mailing list: GARBAGE COLLECTION · CRAFTING INTERPRETERS Whenever we call reallocate() to acquire more memory, we force a collection to run. The if check is because reallocate() is also called to free or shrink an allocation. We don’t want to trigger a GC for that — in particular because the GC itself will call reallocate() to free memory.. Collecting right before allocation is the classic way to wire a GC into a VM. CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE Crafting Interpreters. A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up withnew
INTRODUCTION · CRAFTING INTERPRETERS We’ll write our first interpreter, jlox, in Java. The focus is on concepts. We’ll write the simplest, cleanest code we can to correctly implement the semantics of the language. This will get us comfortable with the basic techniques and also hone our understanding of exactly how the language is supposed to behave. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS In less than two thousand lines of clean Java code, we’ll build a complete interpreter for Lox that implements every single feature of the language, exactly as we’ve specified. The first few chapters work front-to-back through the phases of the interpreter — scanning, parsing, and evaluating code. THE LOX LANGUAGE · CRAFTING INTERPRETERS A static type system is a ton of work to learn and implement. Skipping it gives you a simpler language and a shorter book. We’ll get our interpreter up and executing bits of code sooner if we defer our type checking to runtime. After all, the two languages we’ll be using to implement Lox are both statically typed. OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE Crafting Interpreters. A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up withnew
INTRODUCTION · CRAFTING INTERPRETERS We’ll write our first interpreter, jlox, in Java. The focus is on concepts. We’ll write the simplest, cleanest code we can to correctly implement the semantics of the language. This will get us comfortable with the basic techniques and also hone our understanding of exactly how the language is supposed to behave. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS In less than two thousand lines of clean Java code, we’ll build a complete interpreter for Lox that implements every single feature of the language, exactly as we’ve specified. The first few chapters work front-to-back through the phases of the interpreter — scanning, parsing, and evaluating code. THE LOX LANGUAGE · CRAFTING INTERPRETERS A static type system is a ton of work to learn and implement. Skipping it gives you a simpler language and a shorter book. We’ll get our interpreter up and executing bits of code sooner if we defer our type checking to runtime. After all, the two languages we’ll be using to implement Lox are both statically typed. OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored APPENDIX I · CRAFTING INTERPRETERS Note that block is a statement rule, but is also used as a nonterminal in a couple of other rules for things like function bodies.. A1 . 1 . 3Expressions. Expressions produce values. Lox has a number of unary and binary operators with different levels of precedence. Some grammars for languages do not directly encode the precedence relationships and specify that elsewhere. OPTIMIZATION · CRAFTING INTERPRETERS The evening’s the best part of the day. You’ve done your day’s work. Now you can put your feet up and enjoy it. Kazuo Ishiguro, The Remains of the Day If I still lived in New Orleans, I’d call this chapter a lagniappe, a little something extra given for free to a customer.You’ve got a whole book and a complete virtual machine already, but I want you to have some more fun hacking on clox. A VIRTUAL MACHINE · CRAFTING INTERPRETERS 15 . 1 An Instruction Execution Machine. The virtual machine is one part of our interpreter’s internal architecture. You hand it a chunk of code — literally a Chunk — and it runs it. The code and data structures for the VM reside in a new module. vm.h. A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS In less than two thousand lines of clean Java code, we’ll build a complete interpreter for Lox that implements every single feature of the language, exactly as we’ve specified. The first few chapters work front-to-back through the phases of the interpreter — scanning, parsing, and evaluating code. STRINGS · CRAFTING INTERPRETERS The equality operators also need to gracefully handle strings. Consider: "string" == "string". These are two separate string literals. The compiler will make two separate calls to copyString (), create two distinct ObjString objects and store them as two constants in the chunk. They are different objects in the heap. EVALUATING EXPRESSIONS · CRAFTING INTERPRETERS Given a value of static type Object, we can determine if the runtime value is a number or a string or whatever using Java’s built-in instanceof operator. In other words, the JVM ’s own object representation conveniently gives us everything we need to implement Lox’s built-in types. We’ll have to do a little more work later when we add Lox’s notions of functions, classes, and LOCAL VARIABLES · CRAFTING INTERPRETERS Local variables are one of the most-used parts of a language. If locals are slow, everything is slow. So we want a strategy for local variables that’s as efficient as possible. Function parameters are also heavily used. They work like local variables too, so we’ll use the same implementation technique for them. GARBAGE COLLECTION · CRAFTING INTERPRETERS Throughput is the total fraction of time spent running user code versus doing garbage collection work. Say you run a clox program for ten seconds and it spends a second of that inside collectGarbage (). That means the throughput is 90% — it spent 90% of the time running the program and 10% on GC overhead. CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE Crafting Interpreters. A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up withnew
INTRODUCTION · CRAFTING INTERPRETERS In these pages, we will walk step-by-step through two complete interpreters for a full-featured language. I assume this is your first foray into languages, so I’ll cover each concept and line of code you need to build a complete, usable, fast language implementation. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS Don’t worry, I won’t spam you.) Our Java interpreter, jlox, taught us many of the fundamentals of programming languages, but we still have much to learn. First, if you run any interesting Lox programs in jlox, you’ll discover it’s achingly slow. The style of interpretation it uses — walking the AST directly — is good enoughfor some
LOCAL VARIABLES · CRAFTING INTERPRETERS Local variables are one of the most-used parts of a language. If locals are slow, everything is slow. So we want a strategy for local variables that’s as efficient as possible. Function parameters are also heavily used. They work like local variables too, so we’ll use the same implementation technique for them. CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE Crafting Interpreters. A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up withnew
INTRODUCTION · CRAFTING INTERPRETERS In these pages, we will walk step-by-step through two complete interpreters for a full-featured language. I assume this is your first foray into languages, so I’ll cover each concept and line of code you need to build a complete, usable, fast language implementation. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS Don’t worry, I won’t spam you.) Our Java interpreter, jlox, taught us many of the fundamentals of programming languages, but we still have much to learn. First, if you run any interesting Lox programs in jlox, you’ll discover it’s achingly slow. The style of interpretation it uses — walking the AST directly — is good enoughfor some
LOCAL VARIABLES · CRAFTING INTERPRETERS Local variables are one of the most-used parts of a language. If locals are slow, everything is slow. So we want a strategy for local variables that’s as efficient as possible. Function parameters are also heavily used. They work like local variables too, so we’ll use the same implementation technique for them. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter APPENDIX I · CRAFTING INTERPRETERS Note that block is a statement rule, but is also used as a nonterminal in a couple of other rules for things like function bodies.. A1 . 1 . 3Expressions. Expressions produce values. Lox has a number of unary and binary operators with different levels of precedence. Some grammars for languages do not directly encode the precedence relationships and specify that elsewhere. SCANNING · CRAFTING INTERPRETERS Take big bites. Anything worth doing is worth overdoing. Robert A. Heinlein, Time Enough for Love The first step in any compiler or interpreter is scanning.The scanner takes in raw source code as a series of characters and groups it into a series of chunks we call tokens.These are the meaningful “words” and “punctuation” that make up the language’s grammar. EVALUATING EXPRESSIONS · CRAFTING INTERPRETERS Given a value of static type Object, we can determine if the runtime value is a number or a string or whatever using Java’s built-in instanceof operator. In other words, the JVM ’s own object representation conveniently gives us everything we need to implement Lox’s built-in types. We’ll have to do a little more work later when we add Lox’s notions of functions, classes, and STRINGS · CRAFTING INTERPRETERS The equality operators also need to gracefully handle strings. Consider: "string" == "string". These are two separate string literals. The compiler will make two separate calls to copyString (), create two distinct ObjString objects and store them as two constants in the chunk. They are different objects in the heap. CONTROL FLOW · CRAFTING INTERPRETERS The semicolons in the rules aren’t quoted, which means they are part of the grammar metasyntax, not Lox’s syntax. A block does not have a ; at the end and an if statement doesn’t either, unless the then or else statement happens to be one that ends in a semicolon.. An if statement has an expression for the condition, then a statement to execute if the condition is truthy. A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS In less than two thousand lines of clean Java code, we’ll build a complete interpreter for Lox that implements every single feature of the language, exactly as we’ve specified. The first few chapters work front-to-back through the phases of the interpreter — scanning, parsing, and evaluating code. GARBAGE COLLECTION · CRAFTING INTERPRETERS Throughput is the total fraction of time spent running user code versus doing garbage collection work. Say you run a clox program for ten seconds and it spends a second of that inside collectGarbage (). That means the throughput is 90% — it spent 90% of the time running the program and 10% on GC overhead. INHERITANCE · CRAFTING INTERPRETERS Inheritance appears in object-oriented languages all the way back to the first one, Simula. Early on, Kristen Nygaard and Ole-Johan Dahl noticed commonalities across classes in the simulation programs they wrote. Inheritance gave them a way to reuse the code for those similarparts.
CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE Crafting Interpreters. A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up withnew
INTRODUCTION · CRAFTING INTERPRETERS In these pages, we will walk step-by-step through two complete interpreters for a full-featured language. I assume this is your first foray into languages, so I’ll cover each concept and line of code you need to build a complete, usable, fast language implementation. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS Don’t worry, I won’t spam you.) Our Java interpreter, jlox, taught us many of the fundamentals of programming languages, but we still have much to learn. First, if you run any interesting Lox programs in jlox, you’ll discover it’s achingly slow. The style of interpretation it uses — walking the AST directly — is good enoughfor some
LOCAL VARIABLES · CRAFTING INTERPRETERS Local variables are one of the most-used parts of a language. If locals are slow, everything is slow. So we want a strategy for local variables that’s as efficient as possible. Function parameters are also heavily used. They work like local variables too, so we’ll use the same implementation technique for them. CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE Crafting Interpreters. A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up withnew
INTRODUCTION · CRAFTING INTERPRETERS In these pages, we will walk step-by-step through two complete interpreters for a full-featured language. I assume this is your first foray into languages, so I’ll cover each concept and line of code you need to build a complete, usable, fast language implementation. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns OPTIMIZATION · CRAFTING INTERPRETERS This is another value representation optimization called pointer tagging. If the sign bit is set, then the remaining low bits store the pointer to the Obj: To convert a raw Obj pointer to a Value, we take the pointer and set all of the quiet NaN bits and the sign bit. A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS Don’t worry, I won’t spam you.) Our Java interpreter, jlox, taught us many of the fundamentals of programming languages, but we still have much to learn. First, if you run any interesting Lox programs in jlox, you’ll discover it’s achingly slow. The style of interpretation it uses — walking the AST directly — is good enoughfor some
LOCAL VARIABLES · CRAFTING INTERPRETERS Local variables are one of the most-used parts of a language. If locals are slow, everything is slow. So we want a strategy for local variables that’s as efficient as possible. Function parameters are also heavily used. They work like local variables too, so we’ll use the same implementation technique for them. WELCOME · CRAFTING INTERPRETERS Programming languages encompass a huge space to explore and play in. Plenty of room for your own creations to share with others or just enjoy yourself. Brilliant computer scientists and software engineers have spent entire careers traversing this land without ever reaching the end. If this book is your first entry into the country, welcome. TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter APPENDIX I · CRAFTING INTERPRETERS Note that block is a statement rule, but is also used as a nonterminal in a couple of other rules for things like function bodies.. A1 . 1 . 3Expressions. Expressions produce values. Lox has a number of unary and binary operators with different levels of precedence. Some grammars for languages do not directly encode the precedence relationships and specify that elsewhere. SCANNING · CRAFTING INTERPRETERS Take big bites. Anything worth doing is worth overdoing. Robert A. Heinlein, Time Enough for Love The first step in any compiler or interpreter is scanning.The scanner takes in raw source code as a series of characters and groups it into a series of chunks we call tokens.These are the meaningful “words” and “punctuation” that make up the language’s grammar. EVALUATING EXPRESSIONS · CRAFTING INTERPRETERS Given a value of static type Object, we can determine if the runtime value is a number or a string or whatever using Java’s built-in instanceof operator. In other words, the JVM ’s own object representation conveniently gives us everything we need to implement Lox’s built-in types. We’ll have to do a little more work later when we add Lox’s notions of functions, classes, and STRINGS · CRAFTING INTERPRETERS The equality operators also need to gracefully handle strings. Consider: "string" == "string". These are two separate string literals. The compiler will make two separate calls to copyString (), create two distinct ObjString objects and store them as two constants in the chunk. They are different objects in the heap. CONTROL FLOW · CRAFTING INTERPRETERS The semicolons in the rules aren’t quoted, which means they are part of the grammar metasyntax, not Lox’s syntax. A block does not have a ; at the end and an if statement doesn’t either, unless the then or else statement happens to be one that ends in a semicolon.. An if statement has an expression for the condition, then a statement to execute if the condition is truthy. A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS In less than two thousand lines of clean Java code, we’ll build a complete interpreter for Lox that implements every single feature of the language, exactly as we’ve specified. The first few chapters work front-to-back through the phases of the interpreter — scanning, parsing, and evaluating code. GARBAGE COLLECTION · CRAFTING INTERPRETERS Throughput is the total fraction of time spent running user code versus doing garbage collection work. Say you run a clox program for ten seconds and it spends a second of that inside collectGarbage (). That means the throughput is 90% — it spent 90% of the time running the program and 10% on GC overhead. INHERITANCE · CRAFTING INTERPRETERS Inheritance appears in object-oriented languages all the way back to the first one, Simula. Early on, Kristen Nygaard and Ole-Johan Dahl noticed commonalities across classes in the simulation programs they wrote. Inheritance gave them a way to reuse the code for those similarparts.
CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scriptinglanguage.
WELCOME · CRAFTING INTERPRETERS This book is a work in progress! ×. If you see a mistake, find something unclear, or have a suggestion, please let me know.To follow its progress, please join the mailing list: INTRODUCTION · CRAFTING INTERPRETERSCRAFTING INTERPRETERS PDFCRAFTING INTERPRETERS RUSTCRAFTING COMPILERSCRAFTING INTERPRETERS GITHUBCRAFTING COMPILER Fairy tales are more than true: not because they tell us that dragons exist, but because they tell us that dragons can be beaten. G.K. Chesterton by way of Neil Gaiman, Coraline I’m really excited we’re going on this journey together. TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS This book is a work in progress! ×. If you see a mistake, find something unclear, or have a suggestion, please let me know.To follow its progress, please join the mailing list: LOCAL VARIABLES · CRAFTING INTERPRETERS We have a simple, flat array of all locals that are in scope during each point in the compilation process. They are ordered in the array in the order that their declarations appear in the code. Since the instruction operand we’ll use to encode a local is a single byte, our VM has a hard limit on the number of locals that can be in scopeat once.
A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS This book is a work in progress! ×. If you see a mistake, find something unclear, or have a suggestion, please let me know.To follow its progress, please join the mailing list: CRAFTING INTERPRETERSINTRODUCTIONA MAP OF THE TERRITORYPARSING EXPRESSIONSTABLE OF CONTENTSA VIRTUAL MACHINE A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scriptinglanguage.
WELCOME · CRAFTING INTERPRETERS This book is a work in progress! ×. If you see a mistake, find something unclear, or have a suggestion, please let me know.To follow its progress, please join the mailing list: INTRODUCTION · CRAFTING INTERPRETERSCRAFTING INTERPRETERS PDFCRAFTING INTERPRETERS RUSTCRAFTING COMPILERSCRAFTING INTERPRETERS GITHUBCRAFTING COMPILER Fairy tales are more than true: not because they tell us that dragons exist, but because they tell us that dragons can be beaten. G.K. Chesterton by way of Neil Gaiman, Coraline I’m really excited we’re going on this journey together. TABLE OF CONTENTS · CRAFTING INTERPRETERS Table of Contents. IWelcome; IIA Tree-Walk Interpreter; IIIA Bytecode Virtual Machine Backmatter PARSING EXPRESSIONS · CRAFTING INTERPRETERS In languages like Lox that use IEEE 754 double-precision floating-point numbers, the first evaluates to 0.006, while the second yields 0.006000000000000001.Sometimes that tiny difference matters. This is a good place to learn more.. All of this is correct, but the fact that the first symbol in the body of the rule is the same as the head of the rule means this production is left-recursive. GLOBAL VARIABLES · CRAFTING INTERPRETERS The check() function returns true if the current token has the given type. It seems a little silly to wrap this in a function, but we’ll use it more later, and I think short verb-named functions like this make the parser easier to read.. This sounds trivial, but handwritten parsers for non-toy languages get pretty big. When you have thousands of lines of code, a utility function that turns REPRESENTING CODE · CRAFTING INTERPRETERS To dwellers in a wood, almost every species of tree has its voice as well as its feature. Thomas Hardy, Under the Greenwood Tree In the last chapter, we took the raw source code as a string and transformed it into a slightly higher-level representation: a series of tokens.The parser we’ll write in the next chapter takes those tokens and transforms them yet again, into an even richer, more A TREE-WALK INTERPRETER · CRAFTING INTERPRETERS This book is a work in progress! ×. If you see a mistake, find something unclear, or have a suggestion, please let me know.To follow its progress, please join the mailing list: LOCAL VARIABLES · CRAFTING INTERPRETERS We have a simple, flat array of all locals that are in scope during each point in the compilation process. They are ordered in the array in the order that their declarations appear in the code. Since the instruction operand we’ll use to encode a local is a single byte, our VM has a hard limit on the number of locals that can be in scopeat once.
A BYTECODE VIRTUAL MACHINE · CRAFTING INTERPRETERS This book is a work in progress! ×. If you see a mistake, find something unclear, or have a suggestion, please let me know.To follow its progress, please join the mailing list: INTRODUCTION · CRAFTING INTERPRETERS Fairy tales are more than true: not because they tell us that dragons exist, but because they tell us that dragons can be beaten. G.K. Chesterton by way of Neil Gaiman, Coraline I’m really excited we’re going on this journey together. FUNCTIONS · CRAFTING INTERPRETERS But the name of the function being called isn’t actually part of the call syntax. The thing being called — the callee — can be any expression that evaluates to a function. (Well, it does have to be a pretty high precedence expression, but parentheses take care of that.) For example: The name is part of the call syntax in Pascal. You can call only named functions or functions stored APPENDIX I · CRAFTING INTERPRETERS Note that block is a statement rule, but is also used as a nonterminal in a couple of other rules for things like function bodies.. A1 . 1 . 3Expressions. Expressions produce values. Lox has a number of unary and binary operators with different levels of precedence. Some grammars for languages do not directly encode the precedence relationships and specify that elsewhere. OPTIMIZATION · CRAFTING INTERPRETERS The evening’s the best part of the day. You’ve done your day’s work. Now you can put your feet up and enjoy it. Kazuo Ishiguro, The Remains of the Day If I still lived in New Orleans, I’d call this chapter a lagniappe, a little something extra given for free to a customer.You’ve got a whole book and a complete virtual machine already, but I want you to have some more fun hacking on clox. CALLS AND FUNCTIONS · CRAFTING INTERPRETERS We use our friend ALLOCATE_OBJ() to allocate memory and initialize the object’s header so that the VM knows what type of object it is. Instead of passing in arguments to initialize the function like we did with ObjString, we set the function up in a sort of blank state — zero arity, no name, and no code. That will get filled in later after the function is created. SCANNING · CRAFTING INTERPRETERS Take big bites. Anything worth doing is worth overdoing. Robert A. Heinlein, Time Enough for Love The first step in any compiler or interpreter is scanning.The scanner takes in raw source code as a series of characters and groups it into a series of chunks we call tokens.These are the meaningful “words” and “punctuation” that make up the language’s grammar. A VIRTUAL MACHINE · CRAFTING INTERPRETERS First, we store the chunk being executed in the VM. Then we call run(), an internal helper function that actually runs the bytecode instructions.Between those two parts is an intriguing line. What is this ip business?. As the VM works its way through the bytecode, it keeps track of where it is — the location of the instruction currently being executed. STRINGS · CRAFTING INTERPRETERS This takes a bare Obj pointer and wraps it in a full Value. 19 . 2Struct Inheritance. Every heap-allocated value is an Obj, but Objs are not all the same. For strings, we need the array of characters. EVALUATING EXPRESSIONS · CRAFTING INTERPRETERS Given a value of static type Object, we can determine if the runtime value is a number or a string or whatever using Java’s built-in instanceof operator. In other words, the JVM ’s own object representation conveniently gives us everything we need to implement Lox’s built-in types. We’ll have to do a little more work later when we add Lox’s notions of functions, classes, and CONTROL FLOW · CRAFTING INTERPRETERS The semicolons in the rules aren’t quoted, which means they are part of the grammar metasyntax, not Lox’s syntax. A block does not have a ; at the end and an if statement doesn’t either, unless the then or else statement happens to be one that ends in a semicolon.. An if statement has an expression for the condition, then a statement to execute if the condition is truthy. > A handbook for making programming languages. This book contains everything you need to implement a full-featured, efficient scripting language. You’ll learn both high-level concepts around parsing and semantics and gritty details like bytecode representation and garbage collection. Your brain will light up with new ideas, and your hands will get dirty and calloused. It’s ablast.
Starting from main(), you build a language that features rich syntax, dynamic typing, garbage collection, lexical scope, first-class functions, closures, classes, and inheritance. All packed into a few thousand lines of clean, fast code that you thoroughly understand because you write each one yourself. And you can read the whole book, for free, online:Start Reading!
I WANT TO HOLD THE BOOK IN MY HANDS Call me old-fashioned, but the word “book” to me still implies ink and flattened rectangles of wood pulp. This book is not quite there yet. The chapters are written, but I am still designing the print edition. If you want to know when that’s ready, have I got the mailing list for you: (I post about once a month. Don’t worry, I won’t spam you.)WHO ARE YOU?
I’m Bob Nystrom. I got bitten by the language bug ten years ago when I was on paternity leave with a lot of free time between middle of the night feedings. Since then, I've cobbled together a numberof languages
of
various
ilk
before worming my way into an honest-to-God, full-time programming language job. Today, I work at Google on the Dart language . Before I fell in love with languages, I developed games at Electronic Arts for eight years. I wrote the best-selling book “Game Programming Patterns ” based on what I learned there. You can read that book for free too, because Ilove you.
If you want to get in touch, you can email me at bob at this site's domain or find me (@munificentbob) on
twitter. If you can’t get enough of my writing, I also have a blog . If you like the book, you’ll probably like it too.Details
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