1 files changed, 61 insertions, 0 deletions
diff --git a/21sh/ll-expr/src/lexer/lexer.h b/21sh/ll-expr/src/lexer/lexer.h
new file mode 100644
index 0000000..40a7cc9
--- /dev/null
+++ b/21sh/ll-expr/src/lexer/lexer.h
@@ -0,0 +1,61 @@
+#ifndef LEXER_H
+#define LEXER_H
+
+#include "token.h"
+
+/**
+ * \page Lexer
+ *
+ * The lexer cuts some input text into blocks called tokens.
+
+ * This process is done **on demand**: the lexer doesn't read the
+ * input more than it needs, only creates tokens when lexer_peek
+ * or lexer_pop is called, and no token is available.
+ *
+ * "2 + 3" will produce 3 tokens:
+ *   - TOKEN_NUMBER { .value = 2 }
+ *   - TOKEN_PLUS
+ *   - TOKEN_NUMBER { .value = 3 }
+ */
+
+struct lexer
+{
+    const char *input; // The input data
+    size_t pos; // The current offset inside the input data
+    struct token current_tok; // The next token, if processed
+};
+
+/**
+ * \brief Creates a new lexer given an input string.
+ */
+struct lexer *lexer_new(const char *input);
+
+/**
+ ** \brief Frees the given lexer, but not its input.
+ */
+void lexer_free(struct lexer *lexer);
+
+/**
+ * \brief Returns a token from the input string.
+
+ * This function goes through the input string character by character and
+ * builds a token. lexer_peek and lexer_pop should call it. If the input is
+ * invalid, you must print something on stderr and return the appropriate token.
+ */
+struct token lexer_next_token(struct lexer *lexer);
+
+/**
+ * \brief Returns the next token, but doesn't move forward: calling lexer_peek
+ * multiple times in a row always returns the same result.
+ * This function is meant to help the parser check if the next token matches
+ * some rule.
+ */
+struct token lexer_peek(struct lexer *lexer);
+
+/**
+ * \brief Returns the next token, and removes it from the stream:
+ *   calling lexer_pop in a loop will iterate over all tokens until EOF.
+ */
+struct token lexer_pop(struct lexer *lexer);
+
+#endif /* !LEXER_H */