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* Quick and dirty implementation of with'. with e1; e2' is

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basically desugared to `let <with> = e1; e2', and `lookupVar' looks
  in each <with> in the environment chain for an attribute with the
  specified name.
This commit is contained in:
Eelco Dolstra 2010-03-25 14:51:04 +00:00
parent 3c9f8fc9b6
commit 25eedf085d
2 changed files with 56 additions and 6 deletions
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61
src/libexpr/eval-test.cc
View file

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