1 #ifndef LIB_LEXER_H

     2 #define LIB_LEXER_H

     3 

     4 /*

     5  * Simple FSM lexing

     6  *

     7  * The lexer is implemented as a Finite State Machine, consisting for a number of states, which then contain a set of

     8  * transitions, which move the lexer from state to state based on each char of input at a time.

     9  *

    10  * Whenever the state changes, the token callback is triggered with the collected token data.

    11  */

    12 

    13 #include <sys/types.h>

    14 

    15 /*

    16  * Transition flags

    17  */

    18 enum lex_transition_flags {

    19     LEX_TRANS_DEFAULT   = 0x01,

    20     LEX_TRANS_FINAL     = 0x02,

    21     LEX_TRANS_INVALID   = 0x04,

    22 };

    23 

    24 /*

    25  * A transition from one state to another.

    26  */

    27 struct lex_transition {

    28     // applies to chars [left, right]

    29     char left, right;

    30     

    31     // flags from lex_transition_flags

    32     char flags;

    33     

    34     // next state to enter

    35     int next_state;

    36 };

    37 

    38 /*

    39  * State flags

    40  */ 

    41 enum lex_state_flags {

    42     LEX_STATE_END       = 0x01,

    43 };

    44 

    45 /*

    46  * A state

    47  */

    48 struct lex_state {

    49     // the state name (for debugging)

    50     const char *name;

    51 

    52     // flags from lex_state_flags

    53     char flags;

    54 

    55     // list of transitions for this state, terminated by a transition with next_state=0

    56     struct lex_transition trans_list[15];

    57 };

    58 

    59 /*

    60  * Special tokens

    61  */

    62 

    63 // shows up in token_fn as the value of next_token when this_token is the last token.

    64 #define LEX_EOF 0

    65 

    66 /*

    67  * Lex machine

    68  */

    69 struct lex {

    70     /*

    71      * Core token handler. Everytime a full token is lexed (i.e. the state changes), this will be called.

    72      * `this_token` represents the full token that was parsed, and `token_data` is the token's value. `next_token`

    73      * is the state that terminated this token, and `prev_token` was the token before this one.

    74      *

    75      * `token_data` is a buffer allocated by the lexer that the actual input data is copied into. Thence, it can be

    76      * modified, as its contents will be replaced by the next token. Hence, if you need to keep hold of it, copy it.

    77      *

    78      * Return zero to have lexing continue, nonzero to stop lexing.

    79      */

    80     int (*token_fn) (int this_token, char *token_data, int next_token, int prev_token, void *arg);

    81 

    82     /*

    83      * Called on every char handled by the lexer. `this_token` is the state of the token that the char belongs to.

    84      *

    85      * Return zero to have lexing continue, nonzero to stop lexing.

    86      */

    87     int (*char_fn) (int this_token, char token_char, void *arg);

    88 

    89     /*

    90      * Called when the end of input has been reached, `last_token` is the state that we terminated in.

    91      *

    92      * Return zero to indiciate that the input was valid, nonzero to indicate an error.

    93      */

    94     int (*end_fn) (int last_token, void *arg);

    95     

    96     // number of states

    97     size_t state_count;

    98 

    99     // array of lex_states, indexable by the state id.

   100     struct lex_state state_list[];

   101 };

   102 

   103 /*

   104  * Helper macros for building the state_list

   105  */

   106 #define LEX_STATE(enum_val)     { #enum_val, 0,

   107 #define LEX_STATE_END(enum_val) { #enum_val, LEX_STATE_END,

   108 

   109     #define LEX_CHAR(c, to)         { c, c, 0, to }

   110     #define LEX_RANGE(l, r, to)     { l, r, 0, to }

   111     #define LEX_ALPHA(to)           LEX_RANGE('a', 'z', to), LEX_RANGE('A', 'Z', to)

   112     #define LEX_NUMBER(to)          LEX_RANGE('0', '9', to)

   113     #define LEX_ALNUM(to)           LEX_ALPHA(to), LEX_NUMBER(to), LEX_CHAR('-', to), LEX_CHAR('_', to)

   114     #define LEX_WHITESPACE(to)      LEX_CHAR(' ', to), LEX_CHAR('\n', to), LEX_CHAR('\t', to)

   115     #define LEX_INVALID(c)          { c, c, LEX_TRANS_INVALID, 0 }

   116 

   117     #define LEX_DEFAULT(to)         { 0, 0, LEX_TRANS_DEFAULT, to } \

   118                                   }

   119     #define LEX_END                 { 0, 0, 0, 0 } \

   120                                   }

   121 

   122 /*

   123  * Lex it!

   124  *

   125  * Return zero to indiciate that the input was valid, nonzero otherwise.

   126  */

   127 int lexer (const struct lex *lex, const char *input, void *arg);

   128 

   129 #endif /* LIB_LEXER_H */