1 files changed, 24 insertions, 14 deletions

diff --git a/src/unify.cpp b/src/unify.cpp
index 1b25861..aadc032 100644
--- a/src/unify.cpp
+++ b/src/unify.cpp
@@ -61,7 +61,7 @@ Constraints::constrain(TEnv& tenv, const AST* o, const AType* t)
 	assert(o);
 	assert(t);
 	assert(!o->to<const AType*>());
-	push_back(Constraint(tenv.var(o), t, o->loc));
+	push_back(Constraint(tenv.var(o), t));
 }
 
 template<typename T, typename E>
@@ -73,7 +73,9 @@ substitute(const T* tup, const E* from, const E* to)
 	typename T::iterator ri = ret->begin();
 	FOREACHP(typename T::const_iterator, i, tup) {
 		if (**i == *from) {
-			*ri++ = const_cast<E*>(to);
+			T* type = new T(*to);
+			type->loc = (*i)->loc;
+			*ri++ = type;
 		} else if (static_cast<const E*>(*i) != static_cast<const E*>(to)) {
 			const T* subTup = dynamic_cast<const T*>(*i);
 			if (subTup)
@@ -104,17 +106,24 @@ Subst::compose(const Subst& delta, const Subst& gamma)
 }
 
 /// Replace all occurrences of @a s with @a t
-Constraints
+Constraints&
 Constraints::replace(const AType* s, const AType* t)
 {
-	Constraints cp(*this);
-	for (Constraints::iterator c = begin(); c != end();) {
-		Constraints::iterator next = c; ++next;
-		if (*c->first  == *s) c->first  = t;
-		if (*c->second == *s) c->second = t;
-		c->first = substitute(c->first, s, t);
-		c->second = substitute(c->second, s, t);
-		c = next;
+	for (Constraints::iterator c = begin(); c != end(); ++c) {
+		if (*c->first == *s) {
+			AType* type = new AType(*t);
+			type->loc = c->first->loc;
+			c->first = type;
+		} else {
+			c->first = substitute(c->first, s, t);
+		}
+		if (*c->second == *s) {
+			AType* type = new AType(*t);
+			type->loc = c->second->loc;
+			c->second = type;
+		} else {
+			c->second = substitute(c->second, s, t);
+		}
 	}
 	return *this;
 }
@@ -146,12 +155,13 @@ unify(const Constraints& constraints)
 			if (st->kind == AType::DOTS || tt->kind == AType::DOTS)
 				return unify(cp);
 			else
-				cp.push_back(Constraint(st, tt, st->loc));
+				cp.push_back(Constraint(st, tt));
 		}
 		if (si == s->end() && (ti == t->end() || (*ti)->as<AType*>()->kind == AType::DOTS)
 				|| ti == t->end() && (*si)->as<AType*>()->kind == AType::DOTS)
 			return unify(cp);
 	}
-	throw Error(s->loc ? s->loc : t->loc,
-			(format("type is `%1%' but should be `%2%'") % s->str() % t->str()).str());
+	throw Error(s->loc,
+			(format("type is `%1%' but should be `%2%'\n%3%: error: to match `%4%' here")
+			 % s->str() % t->str() % t->loc.str() % t->str()).str());
 }