#include <u.h>#include <libc.h> #include <sexp.h> O *eval(O *o, O *env); O *evala(O *o, O *env){	O *v;	char *a; 	if(o == nil)		return nil;	if(o->type != Atom)		return nil; 	a = atomstr(o); 	for(v = env; v != nil; v = cdr(v)){		if(strcmp(atomstr(car(car(v))), a) == 0)			return car(cdr(car(v)));	}	return o;} O *evalargs(O *o, O *env){	if(o == nil)		return nil;	if(o->type != List)		return o; 	return cons(eval(car(o), env), evalargs(cdr(o), env));} /* XXX how to do partial application? */O *args2env(O *proto, O *args, O *env){	if(proto == nil)		return env; 	return cons(cons(car(proto), cons(car(args), nil)), args2env(cdr(proto), cdr(args), env));} /* XXX expensive */O *splice(O *head, O *tail){	if(head == nil)		return tail;	return cons(car(head), splice(cdr(head), tail));} O *lambda(O *o, O *env){	O *f, *args; 	if(o == nil)		return nil; 	f = car(o);	if(f == nil)		return nil;	if(f->type != List)		return nil; 	if(strcmp(atomstr(car(f)), "CLOSURE") == 0){		env =  splice(car(cdr(f)), env); /* XXX expensive! especially on every function call! */		args = evalargs(cdr(o), env);		env = args2env(car(cdr(cdr(f))), args, env);		return eval(car(cdr(cdr(cdr(f)))), env);	} 	if(strcmp(atomstr(car(f)), "LAMBDA") == 0){		args = evalargs(cdr(o), env);		//print("lambda\n");		//print("args: "); prin1(args); print("\n");		env = args2env(car(cdr(f)), args, env);		//print("env: "); prin1(env); print("\n");		//print("body: "); prin1(cdr(cdr(f))); print("\n");		//print("evaling body: "); prin1(eval(cdr(cdr(f)), env)); print("\n");		return eval(car(cdr(cdr(f))), env);	} 	print("reached bottom of lambda\n");	return nil;} O *eval(O *o, O *env){	char *a;	O *vars; 	if(o == nil)		return nil;	if(o->type != List)		return evala(o, env); 	o = cons(eval(car(o), env), cdr(o)); 	if(car(o) != nil && car(o)->type == List)		return lambda(o, env); 	a = atomstr(car(o)); 	if(strcmp(a, "CLOSURE") == 0){		return o;	}	if(strcmp(a, "LAMBDA") == 0){		return cons(mka("CLOSURE"), cons(env, cdr(o)));	}	o = cdr(o); 	if(strcmp(a, "CONS") == 0){		o = evalargs(o, env);		return cons(car(o), car(cdr(o)));	}	if(strcmp(a, "CAR") == 0)		return car(eval(car(o), env));	if(strcmp(a, "CDR") == 0)		return cdr(eval(car(o), env));	if(strcmp(a, "IF") == 0){		/* (IF (cond expr) expr) */		if(eval(car(car(o)), env) != nil)			return eval(car(cdr(car(o))), env);		else			return eval(car(cdr(o)), env);	}	if(strcmp(a, "LET") == 0){		/* (let ((x 6) (n 3)) (cond etc...)) */		for(vars = car(o); vars != nil; vars = cdr(vars))			env = cons(cons(car(car(vars)), cons(eval(car(cdr(car(vars))), env), nil)), env);		//prin1(env);		//prin1(car(cdr(o)));		return eval(car(cdr(o)), env);	}	if(strcmp(a, "QUOTE") == 0)		return car(o); 	print("eval reached bottom oops\n");	return nil;}	voidmain(void){	O *o; 	initsexp();	for(;;){		o = eval(r(), nil);		prin1(o);		print("\n");	}	exits(""); }