--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/lib/lex.h	Wed Oct 08 22:05:13 2008 +0300
@@ -0,0 +1,129 @@
+#ifndef LIB_LEXER_H
+#define LIB_LEXER_H
+
+/*
+ * Simple FSM lexing
+ *
+ * The lexer is implemented as a Finite State Machine, consisting for a number of states, which then contain a set of
+ * transitions, which move the lexer from state to state based on each char of input at a time.
+ *
+ * Whenever the state changes, the token callback is triggered with the collected token data.
+ */
+
+#include <sys/types.h>
+
+/*
+ * Transition flags
+ */
+enum lex_transition_flags {
+    LEX_TRANS_DEFAULT   = 0x01,
+    LEX_TRANS_FINAL     = 0x02,
+    LEX_TRANS_INVALID   = 0x04,
+};
+
+/*
+ * A transition from one state to another.
+ */
+struct lex_transition {
+    // applies to chars [left, right]
+    char left, right;
+    
+    // flags from lex_transition_flags
+    char flags;
+    
+    // next state to enter
+    int next_state;
+};
+
+/*
+ * State flags
+ */ 
+enum lex_state_flags {
+    LEX_STATE_END       = 0x01,
+};
+
+/*
+ * A state
+ */
+struct lex_state {
+    // the state name (for debugging)
+    const char *name;
+
+    // flags from lex_state_flags
+    char flags;
+
+    // list of transitions for this state, terminated by a transition with next_state=0
+    struct lex_transition trans_list[15];
+};
+
+/*
+ * Special tokens
+ */
+
+// shows up in token_fn as the value of next_token when this_token is the last token.
+#define LEX_EOF 0
+
+/*
+ * Lex machine
+ */
+struct lex {
+    /*
+     * Core token handler. Everytime a full token is lexed (i.e. the state changes), this will be called.
+     * `this_token` represents the full token that was parsed, and `token_data` is the token's value. `next_token`
+     * is the state that terminated this token, and `prev_token` was the token before this one.
+     *
+     * `token_data` is a buffer allocated by the lexer that the actual input data is copied into. Thence, it can be
+     * modified, as its contents will be replaced by the next token. Hence, if you need to keep hold of it, copy it.
+     *
+     * Return zero to have lexing continue, nonzero to stop lexing.
+     */
+    int (*token_fn) (int this_token, char *token_data, int next_token, int prev_token, void *arg);
+
+    /*
+     * Called on every char handled by the lexer. `this_token` is the state of the token that the char belongs to.
+     *
+     * Return zero to have lexing continue, nonzero to stop lexing.
+     */
+    int (*char_fn) (int this_token, char token_char, void *arg);
+
+    /*
+     * Called when the end of input has been reached, `last_token` is the state that we terminated in.
+     *
+     * Return zero to indiciate that the input was valid, nonzero to indicate an error.
+     */
+    int (*end_fn) (int last_token, void *arg);
+    
+    // number of states
+    size_t state_count;
+
+    // array of lex_states, indexable by the state id.
+    struct lex_state state_list[];
+};
+
+/*
+ * Helper macros for building the state_list
+ */
+#define LEX_STATE(enum_val)     { #enum_val, 0,
+#define LEX_STATE_END(enum_val) { #enum_val, LEX_STATE_END,
+
+    #define LEX_CHAR(c, to)         { c, c, 0, to }
+    #define LEX_RANGE(l, r, to)     { l, r, 0, to }
+    #define LEX_ALPHA(to)           LEX_RANGE('a', 'z', to), LEX_RANGE('A', 'Z', to)
+    #define LEX_NUMBER(to)          LEX_RANGE('0', '9', to)
+    #define LEX_ALNUM(to)           LEX_ALPHA(to), LEX_NUMBER(to), LEX_CHAR('-', to), LEX_CHAR('_', to)
+    #define LEX_WHITESPACE(to)      LEX_CHAR(' ', to), LEX_CHAR('\n', to), LEX_CHAR('\t', to)
+    #define LEX_INVALID(c)          { c, c, LEX_TRANS_INVALID, 0 }
+
+    #define LEX_DEFAULT(to)         { 0, 0, LEX_TRANS_DEFAULT, to } \
+                                  }
+    #define LEX_END                 { 0, 0, 0, 0 } \
+                                  }
+
+/*
+ * Lex it!
+ *
+ * Return zero to indiciate that the input was valid, nonzero otherwise.
+ */
+int lexer (const struct lex *lex, const char *input, void *arg);
+
+#endif /* LIB_LEXER_H */