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Implementing Languages
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Thanks FluentConf
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Thanks SilverStripe
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I Am Not A Special Snowflake
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Compilers Are Not Important
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Great Books On The Subject
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Why Is This Useful?
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Why Is This Useful? ▸ Improving productivity ▸ Communicating in a common domain language ▸ Alternative computational models
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Tools You Can Use
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Tools You Can Use ▸ Compiler generators ▸ String manipulation and state machines
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int minutes = 90;
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Grammar
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Grammar ▸ List of rules which define structure and syntax ▸ Each rule is called a lexeme
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int minutes = 90; e ! type id = value | type id
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Lexer
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Lexer ▸ Breaks code string into tokens ▸ Lexer ignores nesting
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e ! type id = value | type id ["type", "int"], ["id", "minutes"], ["assign", "="], ["value", "90"],
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Parser
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Parser ▸ Arranges tokens in a hierarchy ▸ Checks tokens for syntax errors
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["type", "int"], ["id", "minutes"], ["assign", "="], ["value", "90"], ["definition", [ "int", "minutes", "90", ]]
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Abstract Syntax Tree
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Abstract Syntax Tree ▸ Represents constructs in the compiler's language
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["definition", [ "int", "minutes", "90", ]] new Definition( "int", "minutes", "90", )
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Interpreter
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Interpreter ▸ Calculates immediate effect to context ▸ Always accepts and returns a context
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new Definition( "int", "minutes", "90", ) let context = {}; for (let i = 0; i < objects.length; i++) { context = objects[i].applyTo(context); }
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Compiler
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Compiler ▸ Writes the AST to a new language ▸ Checks constructs for semantic errors in target language
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Recap
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int minutes = 90; e ! type id = value | type id
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e ! type id = value | type id ["type", "int"], ["id", "minutes"], ["assign", "="], ["value", "90"],
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["type", "int"], ["id", "minutes"], ["assign", "="], ["value", "90"], ["definition", [ "int", "minutes", "90", ]]
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["definition", [ "int", "minutes", "90", ]] new Definition( "int", "minutes", "90", )
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new Definition( "int", "minutes", "90", ) let context = {}; for (let i = 0; i < objects.length; i++) { context = objects[i].applyTo(context); }
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Yay!
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Parser Expression Grammar
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Parser Expression Grammar ▸ Uses pattern matching to tokenise and organise lexemes ▸ Generates a reusable interpreter and/or compiler
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{ var context = {}; function __set(key, value) { context[key] = value; } function __get(key) { return context[key]; } }
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start = expression* expression = _ definition _ / _ inspection _ _ "whitespace" = [ \t\r\n]*
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definition "definition" = t:type _ i:id _ assign _ v:value _ terminal { __set(i, v); } / t:type _ i:id _ terminal { __set(i, null); }
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type "type" = "int" id "identity" = letters:[a-z]+ { return letters.join(""); } assign "assign" = "=" value "value" = numbers:[0-9]+ { return parseInt(numbers.join(""), 10); } terminal "terminal" = ";"
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inspection "inspection" = "inspect" _ i:id _ terminal { console.log(__get(i)); }
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Thanks CONFERENCES.OREILLY.COM/FLUENT/JAVASCRIPT-HTML-US/PUBLIC/SCHEDULE/DETAIL/46342 @ASSERTCHRIS