3 files changed, 39 insertions, 3 deletions

diff --git a/src/lexer.c b/src/lexer.c
index 3730620..f937170 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -218,6 +218,20 @@ lexer_load_file_contents(lexer_t *lexer)
 }
 
 void
+lexer_peek_next_token(lexer_t *lexer, token_t *token)
+{
+  uint32_t cur = lexer->cur;
+  uint32_t row = lexer->row;
+  uint32_t bol = lexer->bol;
+
+  lexer_next_token(lexer, token);
+
+  lexer->cur = cur;
+  lexer->row = row;
+  lexer->bol = bol;
+}
+
+void
 lexer_step_back_to(lexer_t *lexer, token_t *token)
 {
   lexer->cur = token->bol + token->col;
diff --git a/src/lexer.h b/src/lexer.h
index d4e84e1..0b9f2ad 100644
--- a/src/lexer.h
+++ b/src/lexer.h
@@ -85,6 +85,9 @@ lexer_drop_char(lexer_t *lexer);
 void
 lexer_step_back_to(lexer_t *lexer, token_t *token);
 
+void
+lexer_peek_next_token(lexer_t *lexer, token_t *token);
+
 char *
 token_kind_to_str(token_kind_t kind);
 
diff --git a/test/lexer_test.c b/test/lexer_test.c
index bbb6784..5326f5c 100644
--- a/test/lexer_test.c
+++ b/test/lexer_test.c
@@ -19,14 +19,14 @@
 #include "munit.h"
 
 void
-make_lexer_from_static_src(lexer_t *lexer, char *src, int srclen)
+make_lexer_from_static_src(lexer_t *lexer, char *src)
 {
   lexer->srclen = 0;
   lexer->cur = 0;
   lexer->row = 0;
   lexer->bol = 0;
   lexer->src = src;
-  lexer->srclen = srclen;
+  lexer->srclen = strlen(src);
 }
 
 void
@@ -34,7 +34,7 @@ assert_token_at(char *source, int token_index, token_kind_t expected_kind, char
 {
   lexer_t lexer;
   token_t token;
-  make_lexer_from_static_src(&lexer, source, strlen(source));
+  make_lexer_from_static_src(&lexer, source);
 
   while (token_index > 0) {
     lexer_next_token(&lexer, &token);
@@ -86,10 +86,29 @@ test_tokenize_unknown(const MunitParameter params[], void *user_data_or_fixture)
   return MUNIT_OK;
 }
 
+static MunitResult
+test_peek_next_token(const MunitParameter params[], void *user_data_or_fixture)
+{
+  lexer_t lexer;
+  make_lexer_from_static_src(&lexer, "()");
+
+  token_t peek_token;
+  lexer_peek_next_token(&lexer, &peek_token);
+
+  token_t next_token;
+  lexer_next_token(&lexer, &next_token);
+
+  assert_int(peek_token.kind, ==, next_token.kind);
+  assert_char((char)peek_token.value.str[0], ==, (char)next_token.value.str[0]);
+
+  return MUNIT_OK;
+}
+
 static MunitTest tests[] = {
   { "/test_tokenize_digit", test_tokenize_number, NULL, NULL, MUNIT_TEST_OPTION_NONE, NULL },
   { "/test_tokenize_op", test_tokenize_op, NULL, NULL, MUNIT_TEST_OPTION_NONE, NULL },
   { "/test_tokenize_unknown", test_tokenize_unknown, NULL, NULL, MUNIT_TEST_OPTION_NONE, NULL },
+  { "/test_peek_next_token", test_peek_next_token, NULL, NULL, MUNIT_TEST_OPTION_NONE, NULL },
   { NULL, NULL, NULL, NULL, MUNIT_TEST_OPTION_NONE, NULL }
 };