f5443d2bf1
This is a complete rewrite of the arithmetics example grammar. It now allows whitespace between tokens, supports "-" and "/" operators, and gets the operator associativity right. Also, rule names now match the usual conventions (term, factor,...). Beside this, the rewrite reflects how I write grammars today (as opposed to few years ago) and what style I would recommend to others.
45 lines
967 B
JavaScript
45 lines
967 B
JavaScript
/*
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* Simple Arithmetics Grammar
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* ==========================
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*
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* Accepts expressions like "2 * (3 + 4)" and computes their value.
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*/
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{
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function combine(first, rest, combiners) {
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var result = first, i;
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for (i = 0; i < rest.length; i++) {
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result = combiners[rest[i][1]](result, rest[i][3]);
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}
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return result;
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}
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}
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Expression
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= first:Term rest:(_ ("+" / "-") _ Term)* {
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return combine(first, rest, {
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"+": function(left, right) { return left + right; },
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"-": function(left, right) { return left - right; }
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});
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}
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Term
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= first:Factor rest:(_ ("*" / "/") _ Factor)* {
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return combine(first, rest, {
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"*": function(left, right) { return left * right; },
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"/": function(left, right) { return left / right; }
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});
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}
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Factor
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= "(" _ expr:Expression _ ")" { return expr; }
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/ Integer
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Integer "integer"
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= [0-9]+ { return parseInt(text(), 10); }
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_ = "whitespace"
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[ \t\n\r]*
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