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#include "bu-parser.h"
#include "tree.h"
#include <stdio.h>
void free_node(node *n) {
if (n->lhs) free_node(n->lhs);
if (n->rhs) free_node(n->rhs);
free(n);
}
void fprint_stack(FILE *stream, struct expr_parser *ep) {
for (size_t i = 0; i < ep->stack_idx; i++) {
struct stackmember m = ep->stack[i];
fprintf(stream, "%zu: %d ", i, m.id);
if (m.id == STACKMEMBER_EXPR) {
fprintTree(stream, m.expr, 0);
} else {
fprintf(stream, "%c\n", m.terminal);
}
}
}
struct expr_parser expr_parser_init(lexer_fn src, void* lex_data) {
return (struct expr_parser){
.lex = src,
.lex_data = lex_data,
.lahead = {0},
.st = PARSER_READY,
.stack = {0},
.stack_idx = 0,
};
}
void expr_parser_finish(struct expr_parser *ep) {
for (size_t i = 0; i < ep->stack_idx; i++) {
if (ep->stack[i].id == STACKMEMBER_EXPR)
free_node(ep->stack[i].expr);
}
}
struct stackmember stack_pos(struct expr_parser *ep, size_t pos) {
ssize_t npos = ep->stack_idx - pos - 1;
if (npos < 0) {
return (struct stackmember)
{ .id = (enum stackmember_id)TOKEN_OOB, .expr = NULL };
}
return ep->stack[npos];
}
void shift(struct expr_parser *ep) {
struct chartoken lahead = ep->lahead;
ep->stack[ep->stack_idx] = (struct stackmember){
.id = (enum stackmember_id)lahead.id,
.terminal = lahead.c,
};
ep->stack_idx++;
ep->lahead = ep->lex(ep->lex_data);
}
#define BAIL_REDUCE_IF(COND, ERRMSG) \
{ if(COND) { \
ep->st = PARSER_ERR; fprintf(stderr, "%s: " ERRMSG "\n", __func__); \
expr_parser_debug_print(stderr, ep); \
return; \
}}
void var_expr(struct expr_parser *ep) {
struct stackmember v = stack_pos(ep, 0);
BAIL_REDUCE_IF(v.id != TOKEN_VARIABLE, "not a variable token");
node *n = malloc(sizeof(node));
*n = (struct node){0};
n->type = LTTR;
n->el = v.terminal;
struct stackmember newm = {
.id = STACKMEMBER_EXPR,
.expr = n,
};
ep->stack[ep->stack_idx - 1] = newm;
}
void binary_expr(struct expr_parser *ep) {
struct stackmember rhs, op, lhs;
lhs = stack_pos(ep, 2);
op = stack_pos(ep, 1);
rhs = stack_pos(ep, 0);
BAIL_REDUCE_IF(
lhs.id != STACKMEMBER_EXPR
|| op.id != TOKEN_BINARY_OPERATOR
|| rhs.id != STACKMEMBER_EXPR,
"incorrect token sequence");
node *n = malloc(sizeof(node));
*n = (struct node){0};
n->type = BIOP;
n->el = op.terminal;
n->lhs = lhs.expr;
n->rhs = rhs.expr;
struct stackmember newm = {
.id = STACKMEMBER_EXPR,
.expr = n,
};
ep->stack_idx -= 2;
ep->stack[ep->stack_idx - 1] = newm;
}
void unary_expr(struct expr_parser *ep) {
struct stackmember op, val;
op = stack_pos(ep, 1);
val = stack_pos(ep, 0);
BAIL_REDUCE_IF(
op.id != TOKEN_UNARY_OPERATOR
|| val.id != STACKMEMBER_EXPR,
"incorrect token sequence");
node *n = malloc(sizeof(node));
*n = (struct node){0};
n->type = UNOP;
n->el = op.terminal;
n->value = val.expr;
struct stackmember newm = {
.id = STACKMEMBER_EXPR,
.expr = n,
};
ep->stack_idx -= 1;
ep->stack[ep->stack_idx - 1] = newm;
}
int expr_parser_run(struct expr_parser *ep) {
// prime the look-ahead
ep->lahead = ep->lex(ep->lex_data);
int noshift = 0;
while (ep->st != PARSER_ERR && ep->st != PARSER_ACCEPT) {
if (!noshift) { shift(ep); }
noshift = 0;
struct stackmember top = stack_pos(ep, 0);
switch (top.id) {
case TOKEN_EOS:
// the result and the EOS token only
if (ep->stack_idx == 2) {
ep->st = PARSER_ACCEPT;
} else {
ep->st = PARSER_ERR;
}
break;
case TOKEN_VARIABLE:
var_expr(ep);
noshift = 1; // check if this enables any reductions first
break;
case STACKMEMBER_EXPR: {
struct stackmember op = stack_pos(ep, 1);
if (op.id == TOKEN_UNARY_OPERATOR) {
unary_expr(ep);
noshift = 1;
} else if (op.id == TOKEN_BINARY_OPERATOR) {
if (op.terminal == '+' && ep->lahead.c == '*') {
break;
}
binary_expr(ep);
noshift = 1;
}
}
break;
default: break;
}
}
return ep->st;
}
void expr_parser_debug_print(FILE *stream, struct expr_parser *ep) {
fprintf(stream,
"PARSER DEBUG DUMP:\n"
"state: %d\n"
"stack: \n", ep->st);
fprint_stack(stream, ep);
}
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