1 files changed, 19 insertions, 2 deletions

diff --git a/src/compiler.c b/src/compiler.c
index fd9e4ae..3ccb86a 100644
--- a/src/compiler.c
+++ b/src/compiler.c
@@ -373,14 +373,17 @@ int amal_compiler_load_file(amal_compiler_options *options, amal_program *progra
     return result;
 }
 
-/* TODO: Verify main func has correct signature */
+/*
+    TODO: Instead of using amal_log_error, print error message with tokenizer to show where the error is.
+    This requires finding tokenizer by code reference.
+*/
 static CHECK_RESULT int validate_main_func(FileScopeReference *main_file_scope, LhsExpr **main_func) {
     const BufferView main_func_name = { "main", 4 };
     LhsExpr *main_func_expr;
 
     main_func_expr = structdecl_get_field_by_name(&main_file_scope->parser->struct_decl, main_func_name);
     if(!main_func_expr) {
-        amal_log_error("main function missing from start file \"%.*s\"", main_file_scope->canonical_path.size, main_file_scope->canonical_path.data);
+        amal_log_error("main function missing from start file \"%.*s\". Note: the main function has to be in the file scope.", main_file_scope->canonical_path.size, main_file_scope->canonical_path.data);
         return AMAL_COMPILER_ERR;
     }
     *main_func = main_func_expr;
@@ -400,6 +403,19 @@ static CHECK_RESULT int validate_main_func(FileScopeReference *main_file_scope,
         return AMAL_COMPILER_ERR;
     }
 
+    {
+        const FunctionDecl *func_decl = main_func_expr->rhs_expr->value.func_decl;
+        if(buffer_get_size(&func_decl->signature->parameters, FunctionParameter) != 0) {
+            amal_log_error("main function in start file \"%.*s\" has to be a closure with no parameters", main_file_scope->canonical_path.size, main_file_scope->canonical_path.data);
+            return AMAL_COMPILER_ERR;
+        }
+
+        if(buffer_get_size(&func_decl->signature->return_types, FunctionReturnType) != 0) {
+            amal_log_error("main function in start file \"%.*s\" has to be a closure that doesn't return anything", main_file_scope->canonical_path.size, main_file_scope->canonical_path.data);
+            return AMAL_COMPILER_ERR;
+        }
+    }
+
     return 0;
 }
 
@@ -437,6 +453,7 @@ int amal_compiler_internal_load_file(amal_compiler *self, const char *filepath,
         */
         LhsExpr *main_func;
 
+        /* Wait for all parsing to be done */
         if(!thread_pool_join_all_tasks(&self->stage_task_thread_pool))
             return -1;
         amal_log_info("Finished parsing all files, resolving AST");