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* Lambdas, applications, substitutions.

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This commit is contained in:
Eelco Dolstra 2003-06-18 12:36:12 +00:00
parent bc57eb3c8a
commit 94cf1f86bb
3 changed files with 71 additions and 4 deletions
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63
src/eval.cc
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@ -247,25 +247,72 @@ void evalArgs(ATermList args, ATermList & argsNF, Environment & env)
env[name] = queryValuePath(parseHash(s));
} else throw badTerm("invalid argument value", eVal);
argsNF = ATappend(argsNF,
argsNF = ATinsert(argsNF,
ATmake("Tup(Str(<str>), <term>)", name.c_str(), eVal));
args = ATgetNext(args);
}
argsNF = ATreverse(argsNF);
}
Expr substExpr(string x, Expr rep, Expr e)
{
char * s;
Expr e2;
if (ATmatch(e, "Var(<str>)", &s))
if (x == s)
return rep;
else
return e;
if (ATmatch(e, "Lam(<str>, <term>)", &s, &e2))
if (x == s)
return e;
/* !!! unfair substitutions */
/* Generically substitute in subterms. */
if (ATgetType(e) == AT_APPL) {
AFun fun = ATgetAFun(e);
int arity = ATgetArity(fun);
ATermList args = ATempty;
for (int i = arity - 1; i >= 0; i--)
args = ATinsert(args, substExpr(x, rep, ATgetArgument(e, i)));
return (ATerm) ATmakeApplList(fun, args);
}
if (ATgetType(e) == AT_LIST) {
ATermList in = (ATermList) e;
ATermList out = ATempty;
while (!ATisEmpty(in)) {
out = ATinsert(out, substExpr(x, rep, ATgetFirst(in)));
in = ATgetNext(in);
}
return (ATerm) ATreverse(out);
}
throw badTerm("do not know how to substitute", e);
}
/* Evaluate an expression. */
Expr evalValue(Expr e)
{
char * s;
Expr eBuildPlatform, eProg, e2;
Expr eBuildPlatform, eProg, e2, e3, e4;
ATermList args;
/* Normal forms. */
if (ATmatch(e, "Str(<str>)", &s) ||
ATmatch(e, "Bool(True)") ||
ATmatch(e, "Bool(False)"))
ATmatch(e, "Bool(False)") ||
ATmatch(e, "Lam(<str>, <term>)", &s, &e2))
return e;
/* Value references. */
@ -282,6 +329,14 @@ Expr evalValue(Expr e)
return evalValue(e3);
}
/* Application. */
if (ATmatch(e, "App(<term>, <term>)", &e2, &e3)) {
e2 = evalValue(e2);
if (!ATmatch(e2, "Lam(<str>, <term>)", &s, &e4))
throw badTerm("expecting lambda", e2);
return evalValue(substExpr(s, e3, e4));
}
/* Execution primitive. */
if (ATmatch(e, "Exec(<term>, <term>, [<list>])",