parser: Create parser for function with return statements

This is a very limited parser implementation which parses a single
function with return type i32 and body containing a return number statement.

The parser doesn't show the 'filepath:row:col' when it fails, a future
improvement would be display it to easy find where the compilation
problem is located.

The ast_nodes are taking the token.value ownership (which is a really
bad design since not all token.value ownership has been taken causing
memory leaking) but we never free them.  For a future fix we could use a
string_view instead since we never change the original source code. The
string_view will also improve the performance a lot avoiding unnecessary
heap memory allocation.

Signed-off-by: Johnny Richard <johnny@johnnyrichard.com>

5 files changed, 182 insertions, 1 deletions

diff --git a/src/lexer.c b/src/lexer.c
index 14165ae..0327ad5 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -198,3 +198,30 @@ lexer_current_char(lexer_t *lexer)
   return lexer->src[lexer->cur];
 }
 
+char *
+token_kind_to_str(token_kind_t kind)
+{
+  switch (kind) {
+    case TOKEN_NAME:
+      return "TOKEN_NAME";
+    case TOKEN_OPAREN:
+      return "(";
+    case TOKEN_CPAREN:
+      return ")";
+    case TOKEN_COLON:
+      return ":";
+    case TOKEN_SEMICOLON:
+      return ";";
+    case TOKEN_OCURLY:
+      return "{";
+    case TOKEN_CCURLY:
+      return "}";
+    case TOKEN_NUMBER:
+      return "TOKEN_NUMBER";
+    case TOKEN_EOF:
+      return "TOKEN_EOF";
+    default:
+      return "UNKNOW_TOKEN";
+  }
+}
+
diff --git a/src/lexer.h b/src/lexer.h
index 29cfc11..f5333a0 100644
--- a/src/lexer.h
+++ b/src/lexer.h
@@ -64,5 +64,7 @@ bool lexer_is_not_eof(lexer_t *lexer);
 
 void lexer_drop_char(lexer_t *lexer);
 
+char * token_kind_to_str(token_kind_t kind);
+
 #endif /* LEXER_H */
 
diff --git a/src/parser.c b/src/parser.c
new file mode 100644
index 0000000..5d2a734
--- /dev/null
+++ b/src/parser.c
@@ -0,0 +1,102 @@
+/*
+* Copyright (C) 2023 Johnny Richard
+*
+* This program is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation, either version 3 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "lexer.h"
+#include "parser.h"
+
+void
+parser_init(parser_t *parser, lexer_t *lexer)
+{
+  assert(parser && "parser must be defined");
+  assert(lexer && "lexer must be defined");
+  parser->lexer = lexer;
+}
+
+static token_t
+expected_token(parser_t *parser, token_kind_t kind)
+{
+  token_t token;
+  lexer_next_token(parser->lexer, &token);
+
+  if (token.kind == TOKEN_EOF) {
+    fprintf(stderr, "[ERROR]: expected '%s' but got end of file\n", token_kind_to_str(kind));
+    exit(EXIT_FAILURE);
+  }
+
+  if (token.kind != kind) {
+    fprintf(stderr, "[ERROR]: expected '%s' but got '%s'\n", token_kind_to_str(kind), token_kind_to_str(token.kind));
+    exit(EXIT_FAILURE);
+  }
+
+  return token;
+}
+
+static type_t
+parser_parse_type(parser_t *parser)
+{
+  token_t token = expected_token(parser, TOKEN_NAME);
+
+  if (strcmp(token.value, "i32") == 0) {
+    return TYPE_I32;
+  }
+
+  fprintf(stderr, "[ERROR]: expected type 'i32' but got '%s'\n", token.value); 
+  exit(EXIT_FAILURE);
+}
+
+static ast_return_stmt_t
+parser_parse_return_stmt(parser_t *parser)
+{
+  expected_token(parser, TOKEN_OCURLY);
+  token_t return_keyword_token = expected_token(parser, TOKEN_NAME);
+
+  if (strcmp(return_keyword_token.value, "return") != 0) {
+    // TODO: Add filename:row:col prefix to expected token exceptions
+    fprintf(stderr, "[ERROR]: expected 'return' keyword but got '%s'\n", return_keyword_token.value); 
+    exit(EXIT_FAILURE);
+  }
+
+  token_t number_token = expected_token(parser, TOKEN_NUMBER);
+  expected_token(parser, TOKEN_SEMICOLON);
+  expected_token(parser, TOKEN_CCURLY);
+
+  return (ast_return_stmt_t) {
+    .number = atoi(number_token.value)
+  };
+}
+
+ast_function_t
+parser_parse_function(parser_t *parser)
+{
+  token_t func_name_token = expected_token(parser, TOKEN_NAME);
+  expected_token(parser, TOKEN_OPAREN);
+  expected_token(parser, TOKEN_CPAREN);
+  expected_token(parser, TOKEN_COLON);
+  type_t return_type = parser_parse_type(parser);
+
+  return (ast_function_t) {
+    // FIXME: alloc memory for the ast_function.name, it's not a good idea to use the token.value
+    .name = func_name_token.value,
+    .return_type = return_type,
+    .body = parser_parse_return_stmt(parser)
+  };
+}
diff --git a/src/parser.h b/src/parser.h
new file mode 100644
index 0000000..e9a1cb7
--- /dev/null
+++ b/src/parser.h
@@ -0,0 +1,45 @@
+/*
+* Copyright (C) 2023 Johnny Richard
+*
+* This program is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation, either version 3 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+#ifndef PARSER_H
+#define PARSER_H
+
+#include "lexer.h"
+
+typedef struct parser_t {
+  lexer_t *lexer;
+} parser_t;
+
+typedef enum {
+  TYPE_I32
+} type_t;
+
+typedef struct ast_return_stmt_t {
+  uint32_t number;
+} ast_return_stmt_t;
+
+typedef struct ast_function_t {
+  char   *name;
+  type_t  return_type;
+  ast_return_stmt_t body;
+} ast_function_t;
+
+void parser_init(parser_t *parser, lexer_t *lexer);
+
+ast_function_t parser_parse_function(parser_t *parser);
+
+#endif /* PARSER_H */
+
diff --git a/src/pipac.c b/src/pipac.c
index f1e5865..0df4a08 100644
--- a/src/pipac.c
+++ b/src/pipac.c
@@ -17,6 +17,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include "lexer.h"
+#include "parser.h"
 
 void
 print_usage()
@@ -46,8 +47,12 @@ main(int argc, char **argv)
   lexer_init(&lexer, filepath);
 
   printf("[INFO]: %ld bytes loaded [filename='%s']\n", lexer.srclen, lexer.filepath);
+  
+  parser_t parser;
+  parser_init(&parser, &lexer);
+  ast_function_t func = parser_parse_function(&parser);
 
-  print_tokens(&lexer);
+  printf("function name='%s' and return type '%d' with value %d\n", func.name, func.return_type, func.body.number);
 
   return EXIT_SUCCESS;
 }