From 429c0bde3e80079ff16637101b16c8a1dd287f53 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Wed, 14 Mar 2018 13:30:20 -0700
Subject: [PATCH] Add syntax sugar for let.

---
 include/lexer.h |  2 ++
 src/lexer.c     |  8 ++++++--
 src/parser.c    | 43 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/include/lexer.h b/include/lexer.h
index b51386f..61c5f10 100644
--- a/include/lexer.h
+++ b/include/lexer.h
@@ -65,6 +65,8 @@ enum libab_lexer_token_e {
     TOKEN_KW_ARROW,
     TOKEN_KW_FUN,
     TOKEN_KW_RETURN,
+    TOKEN_KW_LET,
+    TOKEN_KW_BE,
     TOKEN_LAST
 };
 
diff --git a/src/lexer.c b/src/lexer.c
index 1113d03..48e9252 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -17,7 +17,9 @@ libab_result libab_lexer_init(libab_lexer* lexer) {
         "do",
         "->",
         "fun",
-        "return"
+        "return",
+        "let",
+        "be"
     };
     libab_lexer_token tokens[] = {
         TOKEN_CHAR,
@@ -29,7 +31,9 @@ libab_result libab_lexer_init(libab_lexer* lexer) {
         TOKEN_KW_DO,
         TOKEN_KW_ARROW,
         TOKEN_KW_FUN,
-        TOKEN_KW_RETURN
+        TOKEN_KW_RETURN,
+        TOKEN_KW_LET,
+        TOKEN_KW_BE
     };
     const size_t count = sizeof(tokens)/sizeof(libab_lexer_token);
 
diff --git a/src/parser.c b/src/parser.c
index b1600f4..39b2fab 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -411,6 +411,47 @@ libab_result _parse_fun_param(struct parser_state* state, libab_tree** store_int
     return result;
 }
 
+libab_result _parse_def_fun(struct parser_state* state, libab_tree** store_into) {
+    libab_result result = LIBAB_SUCCESS;
+    libab_tree* temp;
+    if(_parser_is_type(state, TOKEN_KW_LET)) {
+        _parser_state_step(state);
+        if(!_parser_eof(state)) {
+            result = _parser_construct_node_both(state, state->current_match, store_into);
+        } else {
+            result = LIBAB_UNEXPECTED;
+        }
+    } else {
+        result = LIBAB_UNEXPECTED;
+    }
+
+    if(result == LIBAB_SUCCESS) {
+        _parser_state_step(state);
+        (*store_into)->parse_type = NULL;
+        (*store_into)->variant = TREE_FUN;
+        result = _parser_consume_char(state, ':');
+    }
+
+    if(result == LIBAB_SUCCESS) {
+        result = _parse_type(state, &(*store_into)->parse_type);
+    }
+
+    if(result == LIBAB_SUCCESS) {
+        result = _parser_consume_type(state, TOKEN_KW_BE);
+    }
+
+    if(result == LIBAB_SUCCESS) {
+        PARSE_CHILD(result, state, _parse_expression, temp, &(*store_into)->children);
+    }
+
+    if(result != LIBAB_SUCCESS && *store_into) {
+        libab_tree_free_recursive(*store_into);
+        *store_into = NULL;
+    }
+
+    return result;
+}
+
 libab_result _parse_fun(struct parser_state* state, libab_tree** store_into) {
     libab_result result = LIBAB_SUCCESS;
     int is_parenth, is_comma;
@@ -635,6 +676,8 @@ libab_result _parse_atom(struct parser_state* state, libab_tree** store_into) {
         result = _parse_braced_block(state, store_into);
     } else if(_parser_is_type(state, TOKEN_KW_FUN)) {
         result = _parse_fun(state, store_into);
+    } else if(_parser_is_type(state, TOKEN_KW_LET)) {
+        result = _parse_def_fun(state, store_into);
     } else if(_parser_is_type(state, TOKEN_KW_RETURN)) {
         result = _parse_return(state, store_into);
     } else {