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Le code de trois adresses est un moyen d'écrire des instructions. Chaque instruction consiste en:
Newline \r?\n Ws [ \t] Number [0-9]+("."[0-9]+)? String_value \"[^\"]*\" Identifier [A-Za-z][A-Za-z0-9]* %% "var" { return 'VAR'; } "of" { return 'OF'; } "int" { return 'INT'; } "float" { return 'FLOAT'; } "string" { return 'STRING'; } "function" { return 'FUNCTION'; } "endfunction" { return 'END_FUNCTION'; } "=" { return '='; } "-" { return '-'; } "+" { return '+'; } "*" { return '*'; } "/" { return '/'; } "(" { return 'LP'; } ")" { return 'RP'; } ',' { return ','; } {Ws} { /*skip whitespace*/ } {Newline} { return 'NEWLINE'; } {Number} { return 'NUMBER'; } {String_value} { return 'STRING_VALUE'; } {Identifier} { return 'IDENTIFIER'; }
%left '+' '-' // * and / have higher priority %left '*' '/' %% start: expressions { $$ = { type:'script', statements: $1 }; return $$; }; expressions: statement NEWLINE expressions { $3.splice (0, 0, $1); $$ = $3; } | statement NEWLINE { $$ = [$1]; } | statement { $$ = [$1]; }; statement: expr { } | assign { } | function_run { }; expr: '(' expr ')' { $$ = $2; } | expr '+' expr { $$ = { type: 'expr', op: '+', left: $1, right: $3 }; } | expr '-' expr { $$ = { type: 'expr', op: '-', left: $1, right: $3 }; } | expr '*' expr { $$ = { type: 'expr', op: '*', left: $1, right: $3 }; } | expr '/' expr { $$ = { type: 'expr', op: '/', left: $1, right: $3 }; } | IDENTIFIER { $$ = { type: 'id', value: $1 }; } | NUMBER { $$ = { type: 'number', value: parseFloat ($1) }; } | STRING_VALUE { $$ = { type: 'string', value: $1.substring (1, $1.length-2) }; }; assign: IDENTIFIER '=' expr { $$ = { type: 'assign', to: $1, from: $3 }; } | IDENTIFIER '=' function_run { $$ = { type: 'assign', to: $1, from: $3 }; }; function_run: IDENTIFIER 'LP' parameters_run 'RP' { $$ = { type: 'function_run', id: $1, parameters: $3 }; }; parameters_run: expr ',' parameters_run { $3.splice (0, 0, $1); $$ = $3; } | expr { $$ = [$1]; } | { $$ = []; };
"use strict"; // import fs for reading var fs = require ('fs'); // import the generated Parser var parser = require ('./alf.js').parser; var str = fs.readFileSync (process.argv[2], 'UTF-8'); var variable_id = 0; function nextVariable () { return 'variable'+variable_id++; } function writeThreeAddressCode (node) { if (node.type === 'script') { for (var statementIndex in node.statements) { writeThreeAddressCode(node.statements[statementIndex]); } } else if (node.type === 'expr') { if (node.left !== undefined && node.right !== undefined) { writeThreeAddressCode (node.left); writeThreeAddressCode (node.right); // node.left.result is the result of node.left // node.right.result is the result of node.right // write the three address code here } } else if (node.type === 'number') { // the result for a number is the number itself node.result = node.value; } else if (node.type === 'id') { } else if (node.type === 'function_run') { } } var ast = parser.parse (str); console.log (JSON.stringify(ast, null, 4)); writeThreeAddressCode(ast);
Nous voulons transformer l'AST suivant dans une liste de Three Address Code.
if (a > 0) { result = 'positive'; } else { result = 'negative'; }
function double (nr) { return nr*2; } double (7/2);