[PATCH olang v2 3/4] lexer: add token lookahead capability

[Johnny Richard <johnny@johnnyrichard.com>]

In order to skip line breaks (LF) we have to be able to spy the next
token without consume it.

This patch also adds a function to **lexer_peek_next** token, which is
equivalent to **lexer_look_ahead(n = 1)**.

Signed-off-by: Johnny Richard <johnny@johnnyrichard.com>
---
 src/lexer.c | 22 ++++++++++++++++++++++
 src/lexer.h |  6 ++++++
 2 files changed, 28 insertions(+)

diff --git a/src/lexer.c b/src/lexer.c
index b107762..c7756a6 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -233,3 +233,25 @@ lexer_str_to_token_kind(string_view_t text)
 
     return TOKEN_IDENTIFIER;
 }
+
+void
+lexer_peek_next(lexer_t *lexer, token_t *token)
+{
+    lexer_lookahead(lexer, token, 1);
+}
+
+void
+lexer_lookahead(lexer_t *lexer, token_t *token, size_t n)
+{
+    size_t previous_offset = lexer->offset;
+    size_t previous_row = lexer->row;
+    size_t previous_bol = lexer->bol;
+
+    for (size_t i = 0; i < n; ++i) {
+        lexer_next_token(lexer, token);
+    }
+
+    lexer->offset = previous_offset;
+    lexer->row = previous_row;
+    lexer->bol = previous_bol;
+}
diff --git a/src/lexer.h b/src/lexer.h
index 8c09e02..729c957 100644
--- a/src/lexer.h
+++ b/src/lexer.h
@@ -68,6 +68,12 @@ lexer_init(lexer_t *lexer, string_view_t source);
 void
 lexer_next_token(lexer_t *lexer, token_t *token);
 
+void
+lexer_peek_next(lexer_t *lexer, token_t *token);
+
+void
+lexer_lookahead(lexer_t *lexer, token_t *token, size_t n);
+
 char *
 token_kind_to_cstr(token_kind_t kind);
 
-- 
2.43.2