#include "eval.h"

#include "env.h"

#include <assert.h>

static void eval_atom(am_t *am)
{
	switch (am->expr->atom.type) {
	case ATOM_TYPE_EMPTY_LIST:
	case ATOM_TYPE_INTEGER:
	case ATOM_TYPE_PRIM_PROC:
		am->val = am->expr;
		break;
	case ATOM_TYPE_SYMBOL:
		env_fetch(am);
		break;
	}
}

static void eval_list(am_t *am)
{
	am->argl = expr_empty_list(am);
	am->unev = am->expr->pair.cdr;
	am->expr = am->expr->pair.car;

	while (!am->unev->is_atom) {
		am_push(am);
		am->expr = am->unev->pair.cdr;
		am_push(am);
		am->expr = am->argl;
		am_push(am);

		am->expr = am->unev->pair.car;
		eval(am);

		am_pop(am);
		am->argl = am->expr;
		am_append_arg(am);

		am_pop(am);
		am->unev = am->expr;
		am_pop(am);
	}

	assert(am->expr->is_atom);
	assert(am->expr->atom.type == ATOM_TYPE_SYMBOL);
	env_fetch(am);

	assert(am->val->is_atom);
	assert(am->val->atom.type == ATOM_TYPE_PRIM_PROC);
	assert(am->val->atom.prim_proc != NULL);
	am->val->atom.prim_proc(am);
}

void eval(am_t *am)
{
	if (am->expr->is_atom)
		eval_atom(am);
	else
		eval_list(am);
}