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90 lines
2.2 KiB
90 lines
2.2 KiB
/*
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* This module takes a parse tree in a surface format
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* and transforms it into the "core" language which is
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* much simpler and easier to type-check, optimize, and evaluate
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*/
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var typ = require("./representation.js");
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var _ = require("underscore");
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// Lists get desugared to nested function calls
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// i.e. (cons (cons (cons ...)))
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function desugarList(lst) {
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if (lst.xs.length <= 0) {
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return new typ.Nil();
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}
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else {
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var x = desugar(lst.xs[0]);
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var rest = lst.xs.slice(1);
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return new typ.App(new typ.App(new typ.Name("(:)"), x), desugarList(new typ.ListT(rest)));
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}
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}
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function desugarDefFunc(def) {
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return new typ.Def(def.ident,
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curryFunc(def.params,
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def.body));
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}
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function curryFunc(ps, body) {
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if (_.isEmpty(ps)) {
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return desugar(body);
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}
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else {
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return new typ.FuncT(desugar(_.first(ps)),
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curryFunc(_.rest(ps), body));
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}
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}
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function desugarLet(stx) {
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var values = stx.pairs.map(desugar);
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return new typ.LetExp(values, desugar(stx.body));
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}
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function desugar(stx) {
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switch (stx.exprType) {
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case "If":
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if (stx.elseexp)
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return new typ.If(desugar(stx.condition), desugar(stx.thenexp), desugar(stx.elseexp));
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return new typ.If(desugar(stx.condition), desugar(stx.thenexp));
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case "FunctionDefinition":
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return desugarDefFunc(stx);
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case "Definition":
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return new typ.Def(stx.ident, desugar(stx.val));
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case "Name":
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return stx;
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case "Application":
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if ((stx.func.ident === "-" ||
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stx.func.ident === "+") &&
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stx.p) {
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return new typ.UnaryOp(desugar(stx.func), desugar(stx.p));
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}
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if (stx.p)
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return new typ.App(desugar(stx.func), desugar(stx.p));
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return new typ.App(stx.func);
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case "Function":
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return curryFunc(stx.p, stx.body);
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case "List":
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return desugarList(stx);
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case "Bool":
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return stx;
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case "String":
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return stx;
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case "Float":
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return stx;
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case "Integer":
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return stx;
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case "Let":
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return desugarLet(stx);
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default:
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return stx;
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}
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}
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module.exports = { desugar : desugar };
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//var test = typ.ListT([1,2,3]);
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//console.log(desugarList(test));
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