path: root/lex.c

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "common.h"
#include "token.h"

#define emit_error(...) fprintf(stderr, "%s at (%zd,%zd): ", filename, line_number, 1 + column_number);\
                        fprintf(stderr, __VA_ARGS__)

#define BUFFER_SIZE 1024

struct keyword {
	char *s; /* human-readable name of the token, as written by a user */
	enum TOKEN_TYPE t;
};


/** Static defs **************************************************************/

static struct keyword keywords[] = {
	{.s = "module", .t = TOK_MODULE },
	{.s = "input" , .t = TOK_INPUT  },
	{.s = "expr"  , .t = TOK_EXPR   },
	{.s = "or"    , .t = TOK_OR     },
	{.s = "and"   , .t = TOK_AND    },
	{.s = "xor"   , .t = TOK_XOR    },
	{.s = "not"   , .t = TOK_NOT    },
	{.s = "nand"  , .t = TOK_NAND   },
	{.s = "nor"   , .t = TOK_NOR    },
	{.s = NULL                      }
};

static struct keyword token_descriptors[] = {
	{.s = "module declaration"    , .t = TOK_MODULE},
	{.s = "input declaration"     , .t = TOK_INPUT },
	{.s = "expression start"      , .t = TOK_EXPR  },
	{.s = "colon"                 , .t = TOK_COLON },
	{.s = "end of line"           , .t = TOK_EOL   },
	{.s = "binary OR expression"  , .t = TOK_OR    },
	{.s = "binary AND expression" , .t = TOK_AND   },
	{.s = "binary XOR expression" , .t = TOK_XOR   },
	{.s = "binary NAND expression", .t = TOK_NAND  },
	{.s = "binary NOR expression" , .t = TOK_NOR   },
	{.s = "unary NOT expression"  , .t = TOK_NOT   },
	{.s = "identifier"            , .t = TOK_IDENT },
	{.s = NULL                                     }
};

static char buf[BUFFER_SIZE];
static FILE* fd;
static const char *filename = NULL;
static size_t line_number = 0;
static size_t column_number = 0;
static ssize_t leading_whitespace_len = 0;
static struct token *tok_start = NULL;
static struct token *tok_cursor = NULL;


/** Helpers ******************************************************************/

static struct location
get_current_loc(void) {
	struct location l;
	l.line = line_number;
	l.column = column_number + 1;
	l.leading_whitespace_len = leading_whitespace_len == -1 ? 0 : leading_whitespace_len;
	return l;
}

static int
expect(const char c) {
	if (buf[column_number] != c) {
		emit_error("Expected '%c', got '%c'\n", c, buf[column_number]);
		return 1;
	}
	column_number++;
	return 0;
}

static void
eat_whitespace(void) {
	while (column_number < BUFFER_SIZE && (
	           buf[column_number] == ' ' ||
	           buf[column_number] == '\t')) {
		column_number++;
	}
}

static void
add_token(struct token t) {
	struct token *last = tok_cursor;

	if (leading_whitespace_len == -1) {
		leading_whitespace_len = 0;
	}

	tok_cursor = malloc(sizeof(*tok_cursor));
	if (tok_cursor == NULL) {
		emit_error("Internal error: malloc failed:");
		perror("malloc");
		/* FIXME return falsey and propagate error up */
		return;
	}

	*tok_cursor = t;

	/* tok_start is NULL on first token only */
	if (tok_start == NULL) {
		tok_start = tok_cursor;
	} else {
		last->next = tok_cursor;
	}
}

const char *
get_token_description(enum TOKEN_TYPE t) {
	size_t i = 0;

	for (i = 0; i < sizeof(token_descriptors) / sizeof(token_descriptors[0]) && token_descriptors[i].s; i++) {
		if (t == token_descriptors[i].t) {
			return token_descriptors[i].s;
		}
	}

	return "(internal error: unknown token)";
}

/** Beans ********************************************************************/

static struct token
lex_alphanum(void) {
	struct token t;
	size_t i = 0;

	t.loc = get_current_loc();

	i = 0;
	while (i < MAX_IDENT_LENGTH - 1 && isalnum(buf[column_number + i])) {
		t.value[i] = buf[column_number + i];
		i++;
	}
	t.value[i] = '\0';

	column_number += i;
	t.span = i;

	if (i == 0) {
		emit_error("Expected alphanumeric, got '%c'\n", buf[i]);
	}

	/* default to identifier, see below for keyword */
	t.type = TOK_IDENT;

	/* figure out if it's a keyword or not */
	for (i = 0; i < sizeof(keywords) / sizeof(struct keyword) && keywords[i].s; i++) {
		if (strcmp(t.value, keywords[i].s) == 0) {
			t.type = keywords[i].t;
			break;
		}
	}

	return t;
}

static struct token
lex_eol(char eolchar) {
	struct token t;

	t.type = TOK_EOL;
	t.loc = get_current_loc();
	t.span = 1;

	expect(eolchar);

	return t;
}

static struct token
lex_colon(void) {
	struct token t;

	t.type = TOK_COLON;
	t.loc = get_current_loc();
	t.span = 1;

	expect(':');

	return t;
}

static int
lex_line(void) {
	size_t length = strlen(buf);
	leading_whitespace_len = -1;

	while (column_number < length && column_number < strlen(buf)) {
		switch (buf[column_number]) {
			case ':':
				add_token(lex_colon());
				break;
			case ' ':
			case '\t':
				eat_whitespace();
				if (leading_whitespace_len == -1) {
					leading_whitespace_len = column_number;
				}
				break;
			case '\n':
				add_token(lex_eol(buf[column_number]));
				break;
			case '#':
				add_token(lex_eol(buf[column_number]));
				return 0;
				break;
			default:
				/* perform more broad checks */
				if (isalnum(buf[column_number])) {
					add_token(lex_alphanum());
				} else {
					/* nope, still no dice */
					emit_error("Unexpected '%c'\n", buf[column_number]);
					return 1;
				}
				break;
		}
	}
	return 0;
}

struct token *
lex_file(const char *filename_local, FILE *fd_local) {
	struct token start;

	filename = filename_local;
	fd = fd_local;

	line_number = 1;
	tok_cursor = tok_start = NULL;

	start.type = TOK_BEGIN;
	add_token(start);

	while (NULL != fgets(buf, sizeof(buf), fd)) {
		column_number = 0;
		if (lex_line()) {
			return NULL;
		}
		line_number++;
	}

	/* Terminate linked list */
	if (tok_cursor) {
		tok_cursor->next = NULL;
	}

	return tok_start;
}