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eval.c
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eval.c
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#include "common.h"
/*************************************************************
*This file provides two main functions: eval & apply
*************************************************************/
//////////////////////////////////////////////////////
//self_evaluating
//number, boolean, string, character and vector object is self-evaluating.
//////////////////////////////////////////////////////
static cellpoint is_self_evaluating(cellpoint exp)
{
if (is_true(is_number(exp)) || is_true(is_boolean(exp)) ||
is_true(is_null(exp)) || is_true(is_string(exp)) ||
is_true(is_char(exp)) || is_true(is_vector(exp))){
reg = a_true;
}else {
reg = a_false;
}
return reg;
}
////////////////////////////////////////////////////////
//variable
//variables is a symbol object
////////////////////////////////////////////////////////
static cellpoint is_variable(cellpoint exp)
{
return is_symbol(exp);
}
//two args: exp & label
static cellpoint is_tagged_list(void)
{
if (is_true(is_pair(args_ref(1)))){
reg = car(args_ref(1));
args_push(args_ref(2));
args_push(reg);
reg = eq();
}else {
reg = a_false;
}
args_pop(2);
return reg;
}
//////////////////////////////////////////////////////
//quotation
//format: (quote <datum>)
//////////////////////////////////////////////////////
static cellpoint is_quoted(cellpoint exp)
{
reg = exp;
args_push(make_symbol("quote"));
args_push(reg);
reg = is_tagged_list();
return reg;
}
//one arg: exp
static cellpoint quotation_text(void)
{
reg = cdr(args_ref(1));
if (is_true(is_null(reg))){
printf("quote: Bad syntax. in: ");
write(args_ref(1));
newline();
error_handler();
}
reg = car(reg);
args_pop(1);
return reg;
}
//////////////////////////////////////////////////////////
//lambda
//format: (lambda <formal> <body>)
//////////////////////////////////////////////////////////
static cellpoint is_lambda(cellpoint exp)
{
reg = exp;
args_push(make_symbol("lambda"));
args_push(reg);
reg = is_tagged_list();
return reg;
}
//one arg: exp
static cellpoint lambda_parameters(void)
{
reg = args_ref(1);
reg = cdr(reg);
if (is_true(is_null(reg))){
printf("lambda: bad syntax in: ");
write(args_ref(1));
newline();
error_handler();
}
reg = car(reg);
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint lambda_body(void)
{
reg = args_ref(1);
reg = cdr(cdr(reg));
if (is_true(is_null(reg))){
printf("lambda: bad syntax (body can't be empty!) in: ");
write(args_ref(1));
newline();
error_handler();
}
args_pop(1);
return reg;
}
//two args: formals & body
static cellpoint make_lambda(void)
{
reg = cons(args_ref(1), args_ref(2));
stack_push(&vars_stack, reg);
reg = make_symbol("lambda");
reg = cons(reg, stack_pop(&vars_stack));
args_pop(2);
return reg;
}
//one arg: exp
static cellpoint eval_lambda(void)
{
args_push(args_ref(1));
reg = lambda_parameters();
stack_push(&vars_stack, reg);
args_push(args_ref(1));
reg = lambda_body();
stack_push(&vars_stack, reg);
//make a compound procedure object
args_push(current_env);
args_push(stack_pop(&vars_stack));
args_push(stack_pop(&vars_stack));
reg = make_procedure();
args_pop(1);
return reg;
}
/////////////////////////////////////////////////////
//assignment
//format: (set! <var> <value>)
/////////////////////////////////////////////////////
static cellpoint is_assignment(cellpoint exp)
{
reg = exp;
args_push(make_symbol("set!"));
args_push(reg);
reg = is_tagged_list();
return reg;
}
//one arg: exp
static cellpoint assignment_variable(void)
{
reg = args_ref(1);
reg = cdr(reg);
if (is_true(is_null(reg))){
printf("set!: bad syntax (no identifier) in: ");
write(args_ref(1));
newline();
error_handler();
}
reg = car(reg);
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint assignment_value(void)
{
reg = args_ref(1);
reg = cdr(cdr(reg));
if (is_true(is_null(reg))){
printf("set!: bad syntax (missing expression after identifier) in: ");
write(args_ref(1));
newline();
error_handler();
}
reg = car(reg);
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint eval_assignment(void)
{
//calls assignment_variable
args_push(args_ref(1));
reg = assignment_variable();
stack_push(&vars_stack, reg);
//compute assignment value
args_push(args_ref(1));
reg = assignment_value();
args_push(a_false);
args_push(reg);
reg = eval();
stack_push(&vars_stack, reg);
//calls set_var_val
args_push(current_env);
args_push(stack_pop(&vars_stack));
args_push(stack_pop(&vars_stack));
set_var_val();
args_pop(1);
return make_symbol("ok");
}
///////////////////////////////////////////////////////////////
//definition
//format: (define <var> <value>) or
// (define (var <formals>) <body>)
//////////////////////////////////////////////////////////////
static cellpoint is_definition(cellpoint exp)
{
reg = exp;
args_push(make_symbol("define"));
args_push(reg);
reg = is_tagged_list();
return reg;
}
//one arg: exp
static cellpoint definition_variable(void)
{
reg = cdr(args_ref(1));
if (is_true(is_null(reg))){
printf("define: bad syntax in:");
write(args_ref(1));
newline();
error_handler();
}
reg = car(reg);
if (is_false(is_symbol(reg))){
reg = car(reg);
}
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint definition_value(void)
{
if (is_true(is_null(cdr(cdr(args_ref(1)))))){
printf("define: bad syntax in: ");
write(args_ref(1));
newline();
error_handler();
}
reg = car(cdr(args_ref(1)));
if (is_true(is_symbol(reg))){
reg = car(cdr(cdr(args_ref(1))));
}else {
//get formal arguments list
reg = cdr(reg);
stack_push(&vars_stack, reg);
//get body
reg = cdr(cdr(args_ref(1)));
//make a lambda expression
args_push(reg);
args_push(stack_pop(&vars_stack));
reg = make_lambda();
}
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint eval_definition(void)
{
//calls definition_variable
args_push(args_ref(1));
reg = definition_variable();
stack_push(&vars_stack, reg);
//compute definition value
args_push(args_ref(1));
reg = definition_value();
args_push(a_false);
args_push(reg);
reg = eval();
stack_push(&vars_stack, reg);
//calls define_var
args_push(current_env);
args_push(stack_pop(&vars_stack));
args_push(stack_pop(&vars_stack));
define_var();
args_pop(1);
return make_symbol("ok");
}
////////////////////////////////////////////////////////////////
//if
//format: (if <test> <consequent>) or
// (if <test> <consequent> <alternative>)
///////////////////////////////////////////////////////////////
static cellpoint is_if(cellpoint exp)
{
reg = exp;
args_push(make_symbol("if"));
args_push(reg);
reg = is_tagged_list();
return reg;
}
//one arg: exp
static cellpoint if_predicate(void)
{
reg = cdr(args_ref(1));
if (is_true(is_null(reg))){
printf("if: bad syntax in: ");
write(args_ref(1));
newline();
error_handler();
}
reg = car(reg);
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint if_consequent(void)
{
reg = cdr(cdr(args_ref(1)));
if (is_true(is_null(reg))){
printf("if: bad syntax in: ");
write(args_ref(1));
newline();
error_handler();
}
reg = car(reg);
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint if_alternative(void)
{
reg = cdr(cdr(cdr(args_ref(1))));
if (is_true(is_null(reg))){
reg = a_false;
}else {
reg = car(reg);
}
args_pop(1);
return reg;
}
//three args: pred, consq & alter
static cellpoint make_if(void)
{
reg = NIL;
if (is_false(is_null(args_ref(3)))){
reg = cons(args_ref(3), NIL);
}
reg = cons(args_ref(2), reg);
reg = cons(args_ref(1), reg);
reg = cons(make_symbol("if"), reg);
args_pop(3);
return reg;
}
//two args: exp & tail_context
static cellpoint eval_if(void)
{
//computes if_predicate
args_push(args_ref(1));
reg = if_predicate();
//tail_context is a_false
args_push(a_false);
args_push(reg);
reg = eval();
if (is_true(reg)){
//computes if_consequent
args_push(args_ref(1));
reg = if_consequent();
//transmits the tail_context
args_push(args_ref(2));
args_push(reg);
reg = eval();
}else {
//computes if_alternative
args_push(args_ref(1));
reg = if_alternative();
//transmits the tail_context
args_push(args_ref(2));
args_push(reg);
reg = eval();
}
args_pop(2);
return reg;
}
/////////////////////////////////////////////////////////////////
//begin
//format: (begin <exps>)
/////////////////////////////////////////////////////////////////
static cellpoint is_begin(cellpoint exp)
{
reg = exp;
args_push(make_symbol("begin"));
args_push(reg);
reg = is_tagged_list();
return reg;
}
//one arg: exp
static cellpoint begin_actions(void)
{
reg = cdr(args_ref(1));
args_pop(1);
return reg;
}
//one arg: exps
static cellpoint last_exp(void)
{
reg = is_null(cdr(args_ref(1)));
args_pop(1);
return reg;
}
//one arg: exps
static cellpoint first_exp(void)
{
reg = car(args_ref(1));
args_pop(1);
return reg;
}
//one arg: exps
static cellpoint rest_exps(void)
{
reg = cdr(args_ref(1));
args_pop(1);
return reg;
}
//one arg: exps
static cellpoint make_begin(void)
{
reg = make_symbol("begin");
reg = cons(reg, args_ref(1));
args_pop(1);
return reg;
}
//one arg: exps
static cellpoint sequence_2_exp(void)
{
//used in cond_2_if
reg = args_ref(1);
if (is_false(is_null(reg))){
//calls last_exp
args_push(args_ref(1));
reg = last_exp();
if (is_true(reg)){
args_push(args_ref(1));
reg = first_exp();
}else {
args_push(args_ref(1));
reg = make_begin();
}
}
args_pop(1);
return reg;
}
//two args: exps & tail_context
static cellpoint eval_sequence(void)
{
stack_push(&vars_stack, args_ref(1));
args_push(stack_top(&vars_stack));
reg = last_exp();
while (is_false(reg)){
args_push(stack_top(&vars_stack));
reg = first_exp();
//eval the exp which isn't the last one with tail_context is a_false
args_push(a_false);
args_push(reg);
reg = eval();
//renew the remain exps
args_push(stack_pop(&vars_stack));
reg = rest_exps();
stack_push(&vars_stack, reg);
args_push(stack_top(&vars_stack));
reg = last_exp();
}
//get the last expression
args_push(stack_pop(&vars_stack));
reg = first_exp();
//eval the last expression with the second argument (tail_context)
args_push(args_ref(2));
args_push(reg);
reg = eval();
args_pop(2);
return reg;
}
///////////////////////////////////////////////////////////////
//cond
//format: (cond <clause> ...)
///////////////////////////////////////////////////////////////
static cellpoint is_cond(cellpoint exp)
{
reg = exp;
args_push(make_symbol("cond"));
args_push(reg);
reg = is_tagged_list();
return reg;
}
//one arg: exp
static cellpoint cond_clauses(void)
{
reg = cdr(args_ref(1));
args_pop(1);
return reg;
}
//one arg: clause
static cellpoint cond_predicate(void)
{
reg = car(args_ref(1));
args_pop(1);
return reg;
}
//one arg: clause
static cellpoint cond_actions(void)
{
reg = cdr(args_ref(1));
args_pop(1);
return reg;
}
//one arg: clause
static cellpoint is_cond_else_clause(void)
{
//calls cond_predicate
args_push(args_ref(1));
reg = cond_predicate();
stack_push(&vars_stack, reg);
//calls eq
args_push(make_symbol("else"));
args_push(stack_pop(&vars_stack));
reg = eq();
args_pop(1);
return reg;
}
//one arg: clauses
static cellpoint expand_clauses(void)
{
if (is_true(is_null(args_ref(1)))){
reg = a_false;
}else {
args_push(car(args_ref(1)));
reg = is_cond_else_clause();
if (is_true(reg)){
reg = cdr(args_ref(1));
if(is_true(is_null(reg))){
//calls cond_actions
args_push(car(args_ref(1)));
reg = cond_actions();
//calls sequence_2_exp
args_push(reg);
reg = sequence_2_exp();
}else {
printf("Error: ELSE clause isn't last clause in cond expression.\n");
error_handler();
}
}else {
//calls cond_predicate
args_push(car(args_ref(1)));
reg = cond_predicate();
stack_push(&vars_stack, reg);
//calls sequence_2_exp
args_push(car(args_ref(1)));
reg = cond_actions();
args_push(reg);
reg = sequence_2_exp();
stack_push(&vars_stack, reg);
//calls expand_clauses to expand the rest clauses
args_push(cdr(args_ref(1)));
reg = expand_clauses();
//calls make_if
args_push(reg);
args_push(stack_pop(&vars_stack));
args_push(stack_pop(&vars_stack));
reg = make_if();
}
}
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint cond_2_if(void)
{
args_push(args_ref(1));
reg = cond_clauses();
args_push(reg);
reg = expand_clauses();
args_pop(1);
return reg;
}
////////////////////////////////////////////////////////////////
//application
////////////////////////////////////////////////////////////////
static cellpoint is_application(cellpoint exp)
{
reg = is_pair(exp);
return reg;
}
//one arg: exp
static cellpoint operator(void)
{
reg = car(args_ref(1));
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint operands(void)
{
reg = cdr(args_ref(1));
args_pop(1);
return reg;
}
//one arg: ops
static cellpoint no_operands(void)
{
reg = is_null(args_ref(1));
args_pop(1);
return reg;
}
//one arg: ops
static cellpoint first_operand(void)
{
reg = car(args_ref(1));
args_pop(1);
return reg;
}
//one arg: ops
static cellpoint rest_operands(void)
{
reg = cdr(args_ref(1));
args_pop(1);
return reg;
}
//one arg: ops
static cellpoint list_of_values(void)
{
args_push(args_ref(1));
reg = no_operands();
if (is_true(reg)){
reg = NIL;
}else {
//get the first operand
args_push(args_ref(1));
reg = first_operand();
//eval the first operand with tail_context is a_false
args_push(a_false);
args_push(reg);
reg = eval();
stack_push(&vars_stack, reg);
//eval the rest operands
args_push(args_ref(1));
reg = rest_operands();
args_push(reg);
reg = list_of_values();
reg = cons(stack_pop(&vars_stack), reg);
}
args_pop(1);
return reg;
}
//one arg: body
static cellpoint eval_lambda_body(void)
{
stack_push(&vars_stack, args_ref(1));
args_push(stack_top(&vars_stack));
reg = last_exp();
while (is_false(reg)){
args_push(stack_top(&vars_stack));
reg = first_exp();
//eval the exp which isn't the last one with tail_context is a_false
args_push(a_false);
args_push(reg);
reg = eval();
//renew the remain exps
args_push(stack_pop(&vars_stack));
reg = rest_exps();
stack_push(&vars_stack, reg);
args_push(stack_top(&vars_stack));
reg = last_exp();
}
//get the last expression
args_push(stack_pop(&vars_stack));
reg = first_exp();
//eval the last expression with the tail_context is a_true
args_push(a_true);
args_push(reg);
reg = eval();
args_pop(1);
return reg;
}
////////////////////////////////////////////////////////////////
//and & or expressions
///////////////////////////////////////////////////////////////
static cellpoint is_and(cellpoint exp)
{
reg = exp;
args_push(make_symbol("and"));
args_push(reg);
return is_tagged_list();
}
static cellpoint is_or(cellpoint exp)
{
reg = exp;
args_push(make_symbol("or"));
args_push(reg);
return is_tagged_list();
}
//two args: exp & tail_context
static cellpoint eval_and(void)
{
reg = cdr(args_ref(1));
if (is_true(is_null(reg))){
args_pop(2);
return a_true;
}
stack_push(&vars_stack, reg);
while (is_false(is_null(cdr(reg)))){
//evals the expressions which aren't the last expression
args_push(a_false);
args_push(car(reg));
reg = eval();
if (is_false(reg)){
args_pop(2);
return a_false;
}
//renews the remaining expressions
stack_push(&vars_stack, cdr(stack_pop(&vars_stack)));
reg = stack_top(&vars_stack);
}
//evals the last expression
args_push(args_ref(2));
args_push(car(stack_pop(&vars_stack)));
reg = eval();
args_pop(2);
return reg;
}
//two args: exp & tail_context
static cellpoint eval_or(void)
{
reg = cdr(args_ref(1));
if (is_true(is_null(reg))){
args_pop(2);
return a_false;
}
stack_push(&vars_stack, reg);
while (is_false(is_null(cdr(reg)))){
//evals the expressions which aren't the last expression
args_push(a_false);
args_push(car(reg));
reg = eval();
if (is_true(reg)){
args_pop(2);
return reg;
}
//renews the remaining expressions
stack_push(&vars_stack, cdr(stack_pop(&vars_stack)));
reg = stack_top(&vars_stack);
}
//evals the last expressions
args_push(args_ref(2));
args_push(car(stack_pop(&vars_stack)));
reg = eval();
args_pop(2);
return reg;
}
///////////////////////////////////////////////////////////////////
//let expression
///////////////////////////////////////////////////////////////////
static cellpoint is_let(cellpoint exp)
{
reg = exp;
args_push(make_symbol("let"));
args_push(reg);
return is_tagged_list();
}
static void check_bindings(char *proc, cellpoint binding, cellpoint exp)
{
if (is_true(is_list(binding))){
if (is_true(is_symbol(car(binding))) &&
is_false(is_null(cdr(binding))) &&
is_true(is_null(cdr(cdr(binding))))){
return;
}
}
printf("%s: Bad syntax (no an identifier and expression for binding) in: ", proc);
write(exp);
newline();
error_handler();
}
//one arg: exp
static cellpoint let_bindings(void)
{
reg = cdr(args_ref(1));
if (is_true(is_null(reg)) || is_false(is_list(car(reg)))){
printf("let: Bad syntax in: ");
write(args_ref(1));
newline();
error_handler();
}
reg = car(reg);
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint let_vars(void)
{
args_push(args_ref(1));
reg = let_bindings();
stack_push(&vars_stack, NIL);
while (is_false(is_null(reg))){
check_bindings("let", car(reg), args_ref(1));
stack_push(&vars_stack, cons(car(car(reg)), stack_pop(&vars_stack)));
reg = cdr(reg);
}
args_push(stack_pop(&vars_stack));
reg = reverse();
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint let_vals(void)
{
args_push(args_ref(1));
reg = let_bindings();
stack_push(&vars_stack, NIL);
while (is_false(is_null(reg))){
check_bindings("let", car(reg), args_ref(1));
stack_push(&vars_stack, cons(car(cdr(car(reg))), stack_pop(&vars_stack)));
reg = cdr(reg);
}
args_push(stack_pop(&vars_stack));
reg = reverse();
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint let_body(void)
{
reg = cdr(cdr(args_ref(1)));
if (is_true(is_null(reg))){
printf("let: Bad syntax (no expression in body) in: ");
write(args_ref(1));
newline();
error_handler();
}
args_pop(1);
return reg;
}
//two args: bindings & body
static cellpoint make_let(void)
{
reg = cons(args_ref(1), args_ref(2));
reg = cons(make_symbol("let"), reg);
args_pop(2);
return reg;
}
//one arg: exp
static cellpoint let_2_combination(void)
{
//get the binding vals of let expression
args_push(args_ref(1));
reg = let_vals();
stack_push(&vars_stack, reg);
//make a lambda expression
args_push(args_ref(1));
reg = let_vars();
stack_push(&vars_stack, reg);
args_push(args_ref(1));
reg = let_body();
args_push(reg);
args_push(stack_pop(&vars_stack));
reg = make_lambda();
//make a combination
reg = cons(reg, stack_pop(&vars_stack));
args_pop(1);
return reg;
}
///////////////////////////////////////////////////////////////////
//let* expression
///////////////////////////////////////////////////////////////////
static cellpoint is_letstar(cellpoint exp)
{
reg = exp;
args_push(make_symbol("let*"));
args_push(reg);
return is_tagged_list();
}
//one arg: exp
static cellpoint letstar_bindings(void)
{
reg = cdr(args_ref(1));
if (is_true(is_null(reg)) || is_false(is_list(car(reg)))){
printf("let*: Bad syntax in: ");
write(args_ref(1));
newline();
error_handler();
}
reg = car(reg);
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint letstar_body(void)
{
reg = cdr(cdr(args_ref(1)));
if (is_true(is_null(reg))){
printf("let*: Bad syntax (no expression in body) in: ");
write(args_ref(1));
newline();
error_handler();
}
args_pop(1);
return reg;
}
//one arg: exp
static cellpoint letstar_2_nested_lets(void)
{
//get the reverse list of bindings list
args_push(args_ref(1));
reg = letstar_bindings();
args_push(reg);
reg = reverse();
stack_push(&vars_stack, reg);
//get body of let* expression
args_push(args_ref(1));
reg = letstar_body();
//create nested lets
if (is_true(is_null(stack_top(&vars_stack)))){
args_push(reg);
args_push(stack_pop(&vars_stack));
reg = make_let();
}else {
while (is_false(is_null(stack_top(&vars_stack)))){
check_bindings("let*", car(stack_top(&vars_stack)), args_ref(1));
args_push(reg);
args_push(cons(car(stack_top(&vars_stack)), NIL));
reg = make_let();
reg = cons(reg, NIL);
//renews bingdings
stack_push(&vars_stack, cdr(stack_pop(&vars_stack)));
}
stack_pop(&vars_stack);
reg = car(reg);
}
args_pop(1);
return reg;
}
///////////////////////////////////////////////////////////////////
//eval
//requires two arguments:exp & tail_context
///////////////////////////////////////////////////////////////////
cellpoint eval(void)
{
if (is_true(is_self_evaluating(args_ref(1)))){
reg = args_ref(1);
}else if (is_true(is_variable(args_ref(1)))){
reg = args_ref(1);
args_push(current_env);
args_push(reg);
reg = lookup_var_val();
}else if (is_true(is_quoted(args_ref(1)))){
args_push(args_ref(1));
reg = quotation_text();
}else if (is_true(is_assignment(args_ref(1)))){
args_push(args_ref(1));
reg = eval_assignment();
}else if (is_true(is_definition(args_ref(1)))){
args_push(args_ref(1));
reg = eval_definition();
}else if (is_true(is_if(args_ref(1)))){
//eval if expression with the second argument (tail_context)
reg = args_ref(1);
args_push(args_ref(2));
args_push(reg);
reg = eval_if();
}else if (is_true(is_lambda(args_ref(1)))){
args_push(args_ref(1));
reg = eval_lambda();
}else if (is_true(is_begin(args_ref(1)))){
args_push(args_ref(1));
reg = begin_actions();
//eval the actions of begin exp with the second argument (tail_context)
args_push(args_ref(2));
args_push(reg);
reg = eval_sequence();
}else if (is_true(is_cond(args_ref(1)))){
args_push(args_ref(1));
reg = cond_2_if();
//eval the exp with the second argument (tail_context)
args_push(args_ref(2));
args_push(reg);
reg = eval();
}else if (is_true(is_and(args_ref(1)))){
reg = args_ref(1);
args_push(args_ref(2));
args_push(reg);
reg = eval_and();