Make make_case_for throw from the second time on.

Also clean up the errors thrown a little bit.

code/compiler/13/ast.cpp

@@ -228,8 +228,6 @@ struct case_mappings {
     std::optional<std::vector<instruction_ptr>> default_case;
 
     std::vector<instruction_ptr>& make_case_for(tag_type tag) {
-        auto existing_case = defined_cases.find(tag);
-        if(existing_case != defined_cases.end()) return existing_case->second;
         if(default_case)
             throw type_error("attempted pattern match after catch-all");
         return defined_cases[tag];
@@ -279,7 +277,9 @@ struct case_strategy_bool {
         if(!(cpat = dynamic_cast<pattern_constr*>(pt.get())) ||
                 (cpat->constr != "True" && cpat->constr != "False") ||
                 cpat->params.size() != 0)
-            throw type_error("pattern cannot be converted to a boolean");
+            throw type_error(
+                    "pattern cannot be converted to a boolean",
+                    pt->loc);
         return cpat->constr == "True";
     }
 
@@ -321,7 +321,9 @@ struct case_strategy_data {
     repr_type from_typed_pattern(const pattern_ptr& pt, const type* type) {
         pattern_constr* cpat;
         if(!(cpat = dynamic_cast<pattern_constr*>(pt.get())))
-            throw type_error("pattern cannot be interpreted as constructor.");
+            throw type_error(
+                    "pattern cannot be interpreted as constructor.",
+                    pt->loc);
         return std::make_pair(
                 &static_cast<const type_data*>(type)->constructors.find(cpat->constr)->second,
                 &cpat->params);
@@ -383,6 +385,8 @@ void compile_case(const ast_case& node, const env_ptr& env, const type* type, st
     for(auto& branch : node.branches) {
         pattern_var* vpat;
         if((vpat = dynamic_cast<pattern_var*>(branch->pat.get()))) {
+            if(cases.defined_cases_count() == strategy.case_count(type))
+                throw type_error("redundant catch-all pattern", branch->pat->loc);
             auto& branch_into = cases.make_default_case();
             env_ptr new_env(new env_var(branch->expr->env->get_mangled_name(vpat->var), env));
             branch->expr->compile(new_env, branch_into);
@@ -589,5 +593,5 @@ void pattern_constr::typecheck(type_ptr t, type_mgr& mgr, type_env_ptr& env) con
         constructor_type = arr->right;
     }
 
-    mgr.unify(constructor_type, t, loc);
+    mgr.unify(t, constructor_type, loc);
 }