forked from lix-project/lix
* Quick and dirty implementation of with'.
with e1; e2' is
basically desugared to `let <with> = e1; e2', and `lookupVar' looks in each <with> in the environment chain for an attribute with the specified name.
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@ -83,7 +83,7 @@ std::ostream & operator << (std::ostream & str, Value & v)
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static void eval(Env * env, Expr e, Value & v);
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void forceValue(Value & v)
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static void forceValue(Value & v)
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{
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if (v.type == tThunk) {
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v.type = tBlackhole;
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@ -98,12 +98,45 @@ void forceValue(Value & v)
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}
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Value * lookupVar(Env * env, Sym name)
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static Value * lookupWith(Env * env, Sym name)
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{
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for ( ; env; env = env->up) {
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Bindings::iterator i = env->bindings.find(name);
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if (i != env->bindings.end()) return &i->second;
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if (!env) return 0;
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Value * v = lookupWith(env->up, name);
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if (v) return v;
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Bindings::iterator i = env->bindings.find(sWith);
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if (i == env->bindings.end()) return 0;
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Bindings::iterator j = i->second.attrs->find(name);
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if (j != i->second.attrs->end()) return &j->second;
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return 0;
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}
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static Value * lookupVar(Env * env, Sym name)
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{
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/* First look for a regular variable binding for `name'. */
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for (Env * env2 = env; env2; env2 = env2->up) {
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Bindings::iterator i = env2->bindings.find(name);
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if (i != env2->bindings.end()) return &i->second;
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}
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/* Otherwise, look for a `with' attribute set containing `name'.
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Outer `withs' take precedence (i.e. `with {x=1;}; with {x=2;};
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x' evaluates to 1). */
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Value * v = lookupWith(env, name);
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if (v) return v;
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/* Alternative implementation where the inner `withs' take
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precedence (i.e. `with {x=1;}; with {x=2;}; x' evaluates to
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2). */
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#if 0
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for (Env * env2 = env; env2; env2 = env2->up) {
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Bindings::iterator i = env2->bindings.find(sWith);
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if (i == env2->bindings.end()) continue;
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Bindings::iterator j = i->second.attrs->find(name);
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if (j != i->second.attrs->end()) return &j->second;
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}
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#endif
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throw Error("undefined variable");
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}
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@ -112,7 +145,7 @@ unsigned long nrValues = 0;
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unsigned long nrEnvs = 0;
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Env * allocEnv()
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static Env * allocEnv()
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{
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nrEnvs++;
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return new Env;
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@ -264,6 +297,19 @@ static void eval(Env * env, Expr e, Value & v)
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return;
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}
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Expr attrs;
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if (matchWith(e, attrs, body, pos)) {
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Env * env2 = allocEnv();
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env2->up = env;
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Value & vAttrs = env2->bindings[sWith];
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eval(env, attrs, vAttrs);
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if (vAttrs.type != tAttrs) throw TypeError("`with' should evaluate to an attribute set");
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eval(env2, body, v);
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return;
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}
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abort();
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}
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@ -299,6 +345,9 @@ void run(Strings args)
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doTest("({x, y, ...}@args: args.z) { x = 1; y = 2; z = 3; }");
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//doTest("({x ? y, y ? x}: y) { }");
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doTest("let x = 1; in x");
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doTest("with { x = 1; }; x");
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doTest("let x = 2; in with { x = 1; }; x"); // => 2
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doTest("with { x = 1; }; with { x = 2; }; x"); // => 1
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printMsg(lvlError, format("alloced %1% values") % nrValues);
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printMsg(lvlError, format("alloced %1% environments") % nrEnvs);
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@ -95,3 +95,4 @@ eTrue = makeBool(makeTrue())
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eFalse = makeBool(makeFalse())
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sOverrides = toATerm("__overrides")
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sNoAlias = toATerm("")
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sWith = toATerm("<with>")
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