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#ifndef LIB_LEXER_H

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#define LIB_LEXER_H

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/*

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 * Simple FSM lexing

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 *

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

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

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 *

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

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 */

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#include <sys/types.h>

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/*

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 * Transition flags

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 */

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enum lex_transition_flags {

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    LEX_TRANS_DEFAULT   = 0x01,

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    LEX_TRANS_FINAL     = 0x02,

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    LEX_TRANS_INVALID   = 0x04,

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};

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/*

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 * A transition from one state to another.

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 */

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struct lex_transition {

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    // applies to chars [left, right]

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    char left, right;

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    // flags from lex_transition_flags

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    char flags;

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    // next state to enter

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    int next_state;

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};

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/*

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 * State flags

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 */ 

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enum lex_state_flags {

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    LEX_STATE_END       = 0x01,

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};

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/*

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 * A state

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 */

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struct lex_state {

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    // the state name (for debugging)

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    const char *name;

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    // flags from lex_state_flags

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    char flags;

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

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    struct lex_transition trans_list[15];

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};

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/*

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 * Special tokens

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 */

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

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#define LEX_EOF 0

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/*

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 * Lex machine

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 */

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struct lex {

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    /*

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

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

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

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     *

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

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

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     *

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

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     */

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

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    /*

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

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     *

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

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     */

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

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    /*

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

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     *

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

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     */

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

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    // number of states

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    size_t state_count;

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

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    struct lex_state state_list[];

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};

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/*

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 * Helper macros for building the state_list

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 */

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

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

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

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

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

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

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

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

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

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

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                                  }

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

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                                  }

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/*

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 * Lex it!

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 *

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

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 */

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

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#endif /* LIB_LEXER_H */