Pike's Go LL(1) in C

rob_pike_go_ll1_in.c

/*
More than a decade ago, Rob Pike demonstrated a method of LL(1) lexing (not LP, just the L) in Sydny. He used Go, as this
was mostly a demonstration of Go's abilities. However, the basis is applicable to C, as you can see in this code.

You can view the video at: https://www.youtube.com/watch?v=HxaD_trXwRE

I have added two sentinels instead of one (NULL, `nil` in Go) and this is currently extremely barebonse. I plan to use it
to parse PDF's DSL. You can use this method to easily hand-write your own DSLs. That is, if the language grammar is
meant to be parsed using Top-Down parsing, and is not left-recursive. 

To run, just call `gcc -ggdb3 rob_pike_go_ll1_in.c && gdb a.out`

*/

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stddef.h>
#include <limits.h>
#include <wchar.h>
#include <sys/types.h>

#ifdef __GNUC__
#define funcattr_ALWAYS_INLINE static inline __attribute__((always_inline))
#elif _MSV_VER
#define funcattr_ALWAYS_INLINE static inline __forceinline
#endif

#define funcattr_REENTRANT
#define funcattr_ADDRESSABLE

#define sentinel_LEX_ERROR ((void*)-1)
#define sentinel_LEX_TERM ((void*)-2)

#define lexstate_OK(STATE) (STATE != sentinel_LEX_ERROR && STATE != sentinel_LEX_TERM)

typedef wchar_t unicode_t, *unicodestr_t;
typedef uint64_t unicodepos_t;
typedef uint8_t unicodewidth_t;
typedef size_t unicodelen_t;

typedef struct {
	unicodestr_t text;
	unicodelen_t text_size;
	unicodelen_t current_size;
	unicodepos_t current_index;
	unicodewidth_t last_width;
} lexCONTEXT, *lexCONTEXTp;
typedef void *lexSTATEp;
typedef lexSTATEp ((*lexSTATEfn)(lexCONTEXTp));

typedef enum {
	LexSuccess,
	LexFailure,
} lexRESULT;

funcattr_ALWAYS_INLINE
lexSTATEp lex_state_init(lexCONTEXTp lexctx);
funcattr_ALWAYS_INLINE
lexSTATEp lex_state_validate(lexCONTEXTp lexctx);
funcattr_ALWAYS_INLINE
lexSTATEp lex_state_terminate(lexCONTEXTp lexctx);

lexSTATEp lex_state_init(lexCONTEXTp lexctx) {
	lexctx->last_width += 1;
	return lex_state_validate;
}

lexSTATEp lex_state_validate(lexCONTEXTp lexctx) {
	lexctx->last_width += 1;
	return lex_state_terminate;
}

lexSTATEp lex_state_terminate(lexCONTEXTp lexctx) {
	lexctx->last_width += 1;
	return (lexSTATEp)sentinel_LEX_TERM;
}


funcattr_REENTRANT
lexRESULT run_lex_dfa(lexCONTEXTp lexctx, lexSTATEp initfn) {
	lexSTATEp nextstate;
	for (nextstate = (lexSTATEfn)initfn; lexstate_OK(nextstate); nextstate = ((lexSTATEfn)nextstate)(lexctx));
	return (nextstate == sentinel_LEX_ERROR) ? LexFailure : LexSuccess;
}

int main() {
	lexCONTEXT lexctx = {0};
	run_lex_dfa(&lexctx, lex_state_init);
}