Add errors ection to Part 4 of compiler posts

04/CMakeLists.txt

@@ -16,6 +16,7 @@ add_executable(compiler
     ast.cpp ast.hpp definition.cpp
     env.cpp env.hpp
     type.cpp type.hpp
+    error.cpp error.hpp
     ${BISON_parser_OUTPUTS}
     ${FLEX_scanner_OUTPUTS}
     main.cpp

04/ast.cpp

@@ -1,5 +1,6 @@
 #include "ast.hpp"
 #include <ostream>
+#include "error.hpp"
 
 std::string op_name(binop op) {
     switch(op) {
@@ -8,7 +9,7 @@ std::string op_name(binop op) {
         case TIMES: return "*";
         case DIVIDE: return "/";
     }
-    throw 0;
+    return "??";
 }
 
 void print_indent(int n, std::ostream& to) {
@@ -53,7 +54,7 @@ type_ptr ast_binop::typecheck(type_mgr& mgr, const type_env& env) const {
     type_ptr ltype = left->typecheck(mgr, env);
     type_ptr rtype = right->typecheck(mgr, env);
     type_ptr ftype = env.lookup(op_name(op));
-    if(!ftype) throw 0;
+    if(!ftype) throw type_error(std::string("unknown binary operator ") + op_name(op));
 
     type_ptr return_type = mgr.new_type();
     type_ptr arrow_one = type_ptr(new type_arr(rtype, return_type));
@@ -92,9 +93,14 @@ void ast_case::print(int indent, std::ostream& to) const {
 }
 
 type_ptr ast_case::typecheck(type_mgr& mgr, const type_env& env) const {
-    type_ptr case_type = of->typecheck(mgr, env);
+    type_var* var;
+    type_ptr case_type = mgr.resolve(of->typecheck(mgr, env), var);
     type_ptr branch_type = mgr.new_type();
 
+    if(!dynamic_cast<type_base*>(case_type.get())) {
+        throw type_error("attempting case analysis of non-data type");
+    }
+
     for(auto& branch : branches) {
         type_env new_env = env.scope();
         branch->pat->match(case_type, mgr, new_env);
@@ -122,17 +128,17 @@ void pattern_constr::print(std::ostream& to) const {
 
 void pattern_constr::match(type_ptr t, type_mgr& mgr, type_env& env) const {
     type_ptr constructor_type = env.lookup(constr);
-    if(!constructor_type) throw 0;
+    if(!constructor_type) {
+        throw type_error(std::string("pattern using unknown constructor ") + constr);
+    }
 
     for(int i = 0; i < params.size(); i++) {
         type_arr* arr = dynamic_cast<type_arr*>(constructor_type.get());
-        if(!arr) throw 0;
+        if(!arr) throw type_error("too many parameters in constructor pattern");
 
         env.bind(params[i], arr->left);
         constructor_type = arr->right;
     }
 
     mgr.unify(t, constructor_type);
-    type_base* result_type = dynamic_cast<type_base*>(constructor_type.get());
-    if(!result_type) throw 0;
 }

04/error.cpp

@@ -0,0 +1,5 @@
+#include "error.hpp"
+
+const char* type_error::what() const noexcept {
+    return "an error occured while checking the types of the program";
+}

04/error.hpp

@@ -0,0 +1,21 @@
+#pragma once
+#include <exception>
+#include "type.hpp"
+
+struct type_error : std::exception {
+    std::string description;
+
+    type_error(std::string d)
+        : description(std::move(d)) {}
+
+    const char* what() const noexcept override;
+};
+
+struct unification_error : public type_error {
+    type_ptr left;
+    type_ptr right;
+
+    unification_error(type_ptr l, type_ptr r)
+        : left(std::move(l)), right(std::move(r)), 
+            type_error("failed to unify types") {}
+};

04/main.cpp

@@ -1,7 +1,8 @@
 #include "ast.hpp"
-#include "parser.hpp"
-#include "type.hpp"
 #include <iostream>
+#include "parser.hpp"
+#include "error.hpp"
+#include "type.hpp"
 
 void yy::parser::error(const std::string& msg) {
     std::cout << "An error occured: " << msg << std::endl;
@@ -9,10 +10,9 @@ void yy::parser::error(const std::string& msg) {
 
 extern std::vector<definition_ptr> program;
 
-void typecheck_program(const std::vector<definition_ptr>& prog) {
-    type_mgr mgr;
-    type_env env;
-
+void typecheck_program(
+        const std::vector<definition_ptr>& prog,
+        type_mgr& mgr, type_env& env) {
     type_ptr int_type = type_ptr(new type_base("Int")); 
     type_ptr binop_type = type_ptr(new type_arr(
                 int_type,
@@ -40,6 +40,9 @@ void typecheck_program(const std::vector<definition_ptr>& prog) {
 
 int main() {
     yy::parser parser;
+    type_mgr mgr;
+    type_env env;
+
     parser.parse();
     for(auto& definition : program) {
         definition_defn* def = dynamic_cast<definition_defn*>(definition.get());
@@ -51,6 +54,17 @@ int main() {
 
         def->body->print(1, std::cout);
     }
-    typecheck_program(program);
-    std::cout << program.size() << std::endl;
+    try {
+        typecheck_program(program, mgr, env);
+    } catch(unification_error& err) {
+        std::cout << "failed to unify types: " << std::endl;
+        std::cout << "  (1) \033[34m";
+        err.left->print(mgr, std::cout);
+        std::cout << "\033[0m" << std::endl;
+        std::cout << "  (2) \033[32m";
+        err.right->print(mgr, std::cout);
+        std::cout << "\033[0m" << std::endl;
+    } catch(type_error& err) {
+        std::cout << "failed to type check program: " << err.description << std::endl;
+    }
 }

04/type.cpp

@@ -1,6 +1,7 @@
 #include "type.hpp"
 #include <sstream>
 #include <algorithm>
+#include "error.hpp"
 
 void type_var::print(const type_mgr& mgr, std::ostream& to) const {
     auto it = mgr.types.find(name);
@@ -87,7 +88,7 @@ void type_mgr::unify(type_ptr l, type_ptr r) {
         if(lid->name == rid->name) return;
     }
 
-    throw 0;
+    throw unification_error(l, r);
 }
 
 void type_mgr::bind(const std::string& s, type_ptr t) {