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// Copyright (c) 2023, Marvin Borner <dev@marvinborner.de>
// SPDX-License-Identifier: MIT
#include <stdio.h>
#include <term.h>
#include <map.h>
#include <reduce.h>
#include <log.h>
#include <assert.h>
static struct term *substitute(struct term *term, struct term *substitution,
size_t level)
{
if (term->type == VAR) {
if (term->u.var.index == level) {
return substitution;
} else {
term_refer_head(term, substitution->depth);
return term;
}
} else if (term->type == ABS) {
hash_t previous = term->u.abs.term->hash;
struct term *new =
substitute(term->u.abs.term, substitution, level + 1);
if (previous == new->hash)
return term; // nothing changed
struct term *rehashed = term_rehash_abs(term, new);
term_rehash_parents(rehashed);
term_deref_head(term->u.abs.term);
return rehashed;
} else if (term->type == APP) {
hash_t previous_lhs = term->u.app.lhs->hash;
hash_t previous_rhs = term->u.app.rhs->hash;
struct term *lhs =
substitute(term->u.app.lhs, substitution, level);
struct term *rhs =
substitute(term->u.app.rhs, substitution, level);
if (previous_lhs == lhs->hash && previous_rhs == rhs->hash)
return term; // nothing changed
struct term *rehashed = term_rehash_app(term, lhs, rhs);
term_rehash_parents(rehashed);
return rehashed;
}
fatal("invalid type %d\n", term->type);
}
// reduction of application
// ([X] Y) -> X/Y
struct term *reduce(struct term *term)
{
if (!term_is_beta_redex(term))
fatal("can't reduce non-beta-redex %d\n", term->type);
/* map_delete(term->u.app.lhs->parents, term); */
/* map_delete(term->u.app.rhs->parents, term); */
struct term *reduced = substitute(term->u.app.lhs, term->u.app.rhs, -1);
/* term_deref_head(term); */
return reduced;
}
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