public SubstMap unify(final Loc loc, final Type other, final TypeEnv env) {
if (env.checkVisited(this, other)) return SubstMap.EMPTY;
if (other instanceof TypeVar) return SubstMap.bindVar(loc, (TypeVar) other, this);
// if our application expression can be evaluated, unify against that.
if (isAbsApply()) return eval().unify(loc, other, env);
final Type otherEval = other.deref().eval();
if (otherEval instanceof TypeApp) {
final TypeApp otherApp = (TypeApp) otherEval;
final SubstMap baseSubst = base.unify(loc, otherApp.base, env);
if (baseSubst != null) {
final SubstMap argSubst =
arg.subst(baseSubst).unify(loc, otherApp.arg.subst(baseSubst), env);
if (argSubst != null) return baseSubst.compose(loc, argSubst);
}
} else if (kind.equals(otherEval.getKind())) {
// other is not an application expression, but kinds match.
// other type classes do opportunistic matching of type apps
// implementations of unify. This approach is really ad-hoc,
// needs to be rationalized.
return otherEval.unify(loc, this, env);
}
return null;
}
public Type eval() {
if (reduced != null) return reduced;
if (inEval) return this;
final Type baseEval = base.deref().eval();
final Type argEval = arg.deref().eval();
if (!(baseEval instanceof TypeCons))
// error has been raised
return this;
final TypeCons cons = (TypeCons) baseEval;
final Type body = cons.getBody();
if (body == null) return reduced(baseEval, argEval);
// check base abs param kind against arg kind
if (!checkKindAgreement(cons, argEval))
// error has been raised
return this;
// evaluate by building param->arg subst map and
// applying it to body term
final SubstMap argMap = new SubstMap();
final Collection<TypeParam> params = body.getParams().values();
if (params.size() == 1) {
final TypeParam param = params.iterator().next();
assert param.getTypeScope() == body : "nope";
argMap.put(param, argEval);
} else {
if (!(argEval instanceof TypeTuple)) assert false;
final Iterator<Type> argList = ((TypeTuple) argEval).getMembers().iterator();
for (final TypeParam param : params) {
assert param.getTypeScope() == body : "nope";
argMap.put(param, argList.next());
}
}
final Type bodySubst = new TypeApplier(body, argMap).apply();
// evaluate body with args substituted for params
inEval = true;
reduced = bodySubst.eval();
inEval = false;
if (Session.isDebug())
Session.debug(
body.getLoc(), "eval {0}({1}) => {2}", body.dump(), argMap.dump(), reduced.dump());
return reduced;
}