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// Copyright (c) 2023, Marvin Borner <dev@marvinborner.de>
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
#include <term.h>
#include <gc.h>
static int name_generator(void)
{
static int current = 0x4242; // TODO: idk?
return current++;
}
#define MAX_CONVERSION_VARS 256
static void to_barendregt_helper(struct term *term, int *vars, int size)
{
assert(size < MAX_CONVERSION_VARS);
switch (term->type) {
case ABS:
vars[size] = name_generator();
term->u.abs.name = vars[size];
to_barendregt_helper(term->u.abs.term, vars, size + 1);
break;
case APP:
to_barendregt_helper(term->u.app.lhs, vars, size);
to_barendregt_helper(term->u.app.rhs, vars, size);
break;
case VAR:
if (term->u.var.type == BARENDREGT_VARIABLE)
break;
int ind = size - term->u.var.name - 1;
if (ind < 0) {
fprintf(stderr, "Unbound variable %d\n",
term->u.var.name);
term->u.var.name = name_generator();
} else {
term->u.var.name = vars[size - term->u.var.name - 1];
}
term->u.var.type = BARENDREGT_VARIABLE;
break;
default:
fprintf(stderr, "Invalid type %d\n", term->type);
}
}
static void to_bruijn_helper(struct term *term, int *vars, int size)
{
assert(size < MAX_CONVERSION_VARS);
switch (term->type) {
case ABS:
vars[size] = term->u.abs.name;
to_bruijn_helper(term->u.abs.term, vars, size + 1);
term->u.abs.name = 0;
break;
case APP:
to_bruijn_helper(term->u.app.lhs, vars, size);
to_bruijn_helper(term->u.app.rhs, vars, size);
break;
case VAR:
if (term->u.var.type == BRUIJN_INDEX)
break;
int ind = -1;
for (int i = 0; i < size; i++) {
if (vars[i] == term->u.var.name) {
ind = i;
break;
}
}
if (ind < 0) {
fprintf(stderr, "Unbound variable %d\n",
term->u.var.name);
}
term->u.var.name = size - ind - 1;
term->u.var.type = BRUIJN_INDEX;
break;
default:
fprintf(stderr, "Invalid type %d\n", term->type);
}
}
void to_barendregt(struct term *term)
{
int vars[MAX_CONVERSION_VARS] = { 0 };
to_barendregt_helper(term, vars, 0);
}
void to_bruijn(struct term *term)
{
int vars[MAX_CONVERSION_VARS] = { 0 };
to_bruijn_helper(term, vars, 0);
}
struct term *new_term(term_type type)
{
struct term *term = gc_calloc(&gc, 1, sizeof(*term));
if (!term) {
fprintf(stderr, "Out of memory!\n");
abort();
}
term->type = type;
return term;
}
struct term *duplicate_term(struct term *term)
{
switch (term->type) {
case ABS:;
struct term *abs = new_term(ABS);
abs->u.abs.name = term->u.abs.name;
abs->u.abs.term = duplicate_term(term->u.abs.term);
return abs;
case APP:;
struct term *app = new_term(APP);
app->u.app.lhs = duplicate_term(term->u.app.lhs);
app->u.app.rhs = duplicate_term(term->u.app.rhs);
return app;
case VAR:;
struct term *var = new_term(VAR);
var->u.var.name = term->u.var.name;
var->u.var.type = term->u.var.type;
return var;
default:
fprintf(stderr, "Invalid type %d\n", term->type);
}
return term;
}
int alpha_equivalency(struct term *a, struct term *b)
{
if (a->type != b->type)
return 0;
switch (a->type) {
case ABS:
assert(!a->u.abs.name); // TODO: Only bruijn right now
return a->u.abs.name == b->u.abs.name &&
alpha_equivalency(a->u.abs.term, b->u.abs.term);
case APP:
return alpha_equivalency(a->u.app.lhs, b->u.app.lhs) &&
alpha_equivalency(a->u.app.rhs, b->u.app.rhs);
case VAR:;
assert(a->u.var.type == BRUIJN_INDEX &&
b->u.var.type == BRUIJN_INDEX);
return a->u.var.name == b->u.var.name;
default:
fprintf(stderr, "Invalid type %d\n", a->type);
}
return 0;
}
void free_term(struct term *term)
{
switch (term->type) {
case ABS:
free_term(term->u.abs.term);
gc_free(&gc, term);
break;
case APP:
free_term(term->u.app.lhs);
free_term(term->u.app.rhs);
gc_free(&gc, term);
break;
case VAR:
gc_free(&gc, term);
break;
default:
fprintf(stderr, "Invalid type %d\n", term->type);
}
}
void print_term(struct term *term)
{
switch (term->type) {
case ABS:
if (term->u.abs.name)
printf("[{%d} ", term->u.abs.name);
else
printf("[");
print_term(term->u.abs.term);
printf("]");
break;
case APP:
printf("(");
print_term(term->u.app.lhs);
printf(" ");
print_term(term->u.app.rhs);
printf(")");
break;
case VAR:
printf("%d", term->u.var.name);
break;
default:
fprintf(stderr, "Invalid type %d\n", term->type);
}
}
void print_scheme(struct term *term)
{
switch (term->type) {
case ABS:
printf("(*lam \"%d\" ", term->u.abs.name);
print_scheme(term->u.abs.term);
printf(")");
break;
case APP:
printf("(*app ");
print_scheme(term->u.app.lhs);
printf(" ");
print_scheme(term->u.app.rhs);
printf(")");
break;
case VAR:
printf("(*var \"%d\")", term->u.var.name);
break;
default:
fprintf(stderr, "Invalid type %d\n", term->type);
}
}
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