ref: 2f9d6593d40d5756034344a7456d6bec80c5873e
dir: /tiny/eval1/
value_t eval_sexpr(value_t e, value_t *penv)
{
value_t f, v, bind, headsym, asym, labl=0, *pv, *argsyms, *body, *lenv;
value_t *rest;
cons_t *c;
symbol_t *sym;
u_int32_t saveSP;
int i, nargs, noeval=0;
number_t s, n;
if (issymbol(e)) {
sym = (symbol_t*)ptr(e);
if (sym->constant != UNBOUND) return sym->constant;
v = *penv;
while (iscons(v)) {
bind = car_(v);
if (iscons(bind) && car_(bind) == e)
return cdr_(bind);
v = cdr_(v);
}
if ((v = sym->binding) == UNBOUND)
lerror("eval: error: variable %s has no value\n", sym->name);
return v;
}
if ((unsigned)(char*)&nargs < (unsigned)stack_bottom || SP>=(N_STACK-100))
lerror("eval: error: stack overflow\n");
saveSP = SP;
PUSH(e);
f = eval(car_(e), penv);
if (isbuiltin(f)) {
// handle builtin function
if (!isspecial(f)) {
// evaluate argument list, placing arguments on stack
v = Stack[saveSP] = cdr_(Stack[saveSP]);
while (iscons(v)) {
v = eval(car_(v), penv);
PUSH(v);
v = Stack[saveSP] = cdr_(Stack[saveSP]);
}
}
apply_builtin:
nargs = SP - saveSP - 1;
switch (intval(f)) {
// special forms
case F_QUOTE:
v = cdr_(Stack[saveSP]);
if (!iscons(v))
lerror("quote: error: expected argument\n");
v = car_(v);
break;
case F_MACRO:
case F_LAMBDA:
v = Stack[saveSP];
if (*penv != NIL) {
// build a closure (lambda args body . env)
v = cdr_(v);
PUSH(car(v));
argsyms = &Stack[SP-1];
PUSH(car(cdr_(v)));
body = &Stack[SP-1];
v = cons_(intval(f)==F_LAMBDA ? &LAMBDA : &MACRO,
cons(argsyms, cons(body, penv)));
}
break;
case F_LABEL:
v = Stack[saveSP];
if (*penv != NIL) {
v = cdr_(v);
PUSH(car(v)); // name
pv = &Stack[SP-1];
PUSH(car(cdr_(v))); // function
body = &Stack[SP-1];
*body = eval(*body, penv); // evaluate lambda
v = cons_(&LABEL, cons(pv, cons(body, &NIL)));
}
break;
case F_IF:
v = car(cdr_(Stack[saveSP]));
if (eval(v, penv) != NIL)
v = car(cdr_(cdr_(Stack[saveSP])));
else
v = car(cdr(cdr_(cdr_(Stack[saveSP]))));
v = eval(v, penv);
break;
case F_COND:
Stack[saveSP] = cdr_(Stack[saveSP]);
pv = &Stack[saveSP]; v = NIL;
while (iscons(*pv)) {
c = tocons(car_(*pv), "cond");
if ((v=eval(c->car, penv)) != NIL) {
*pv = cdr_(car_(*pv));
// evaluate body forms
while (iscons(*pv)) {
v = eval(car_(*pv), penv);
*pv = cdr_(*pv);
}
break;
}
*pv = cdr_(*pv);
}
break;
case F_AND:
Stack[saveSP] = cdr_(Stack[saveSP]);
pv = &Stack[saveSP]; v = T;
while (iscons(*pv)) {
if ((v=eval(car_(*pv), penv)) == NIL)
break;
*pv = cdr_(*pv);
}
break;
case F_OR:
Stack[saveSP] = cdr_(Stack[saveSP]);
pv = &Stack[saveSP]; v = NIL;
while (iscons(*pv)) {
if ((v=eval(car_(*pv), penv)) != NIL)
break;
*pv = cdr_(*pv);
}
break;
case F_WHILE:
PUSH(car(cdr(cdr_(Stack[saveSP]))));
body = &Stack[SP-1];
Stack[saveSP] = car_(cdr_(Stack[saveSP]));
value_t *cond = &Stack[saveSP];
PUSH(NIL); pv = &Stack[SP-1];
while (eval(*cond, penv) != NIL)
*pv = eval(*body, penv);
v = *pv;
break;
case F_PROGN:
// return last arg
Stack[saveSP] = cdr_(Stack[saveSP]);
pv = &Stack[saveSP]; v = NIL;
while (iscons(*pv)) {
v = eval(car_(*pv), penv);
*pv = cdr_(*pv);
}
break;
// ordinary functions
case F_SET:
argcount("set", nargs, 2);
e = Stack[SP-2];
v = *penv;
while (iscons(v)) {
bind = car_(v);
if (iscons(bind) && car_(bind) == e) {
cdr_(bind) = (v=Stack[SP-1]);
SP=saveSP; return v;
}
v = cdr_(v);
}
tosymbol(e, "set")->binding = (v=Stack[SP-1]);
break;
case F_BOUNDP:
argcount("boundp", nargs, 1);
if (tosymbol(Stack[SP-1], "boundp")->binding == UNBOUND)
v = NIL;
else
v = T;
break;
case F_EQ:
argcount("eq", nargs, 2);
v = ((Stack[SP-2] == Stack[SP-1]) ? T : NIL);
break;
case F_CONS:
argcount("cons", nargs, 2);
v = mk_cons();
car_(v) = Stack[SP-2];
cdr_(v) = Stack[SP-1];
break;
case F_CAR:
argcount("car", nargs, 1);
v = car(Stack[SP-1]);
break;
case F_CDR:
argcount("cdr", nargs, 1);
v = cdr(Stack[SP-1]);
break;
case F_RPLACA:
argcount("rplaca", nargs, 2);
car(v=Stack[SP-2]) = Stack[SP-1];
break;
case F_RPLACD:
argcount("rplacd", nargs, 2);
cdr(v=Stack[SP-2]) = Stack[SP-1];
break;
case F_ATOM:
argcount("atom", nargs, 1);
v = ((!iscons(Stack[SP-1])) ? T : NIL);
break;
case F_SYMBOLP:
argcount("symbolp", nargs, 1);
v = ((issymbol(Stack[SP-1])) ? T : NIL);
break;
case F_NUMBERP:
argcount("numberp", nargs, 1);
v = ((isnumber(Stack[SP-1])) ? T : NIL);
break;
case F_ADD:
s = 0;
for (i=saveSP+1; i < (int)SP; i++) {
n = tonumber(Stack[i], "+");
s += n;
}
v = number(s);
break;
case F_SUB:
if (nargs < 1)
lerror("-: error: too few arguments\n");
i = saveSP+1;
s = (nargs==1) ? 0 : tonumber(Stack[i++], "-");
for (; i < (int)SP; i++) {
n = tonumber(Stack[i], "-");
s -= n;
}
v = number(s);
break;
case F_MUL:
s = 1;
for (i=saveSP+1; i < (int)SP; i++) {
n = tonumber(Stack[i], "*");
s *= n;
}
v = number(s);
break;
case F_DIV:
if (nargs < 1)
lerror("/: error: too few arguments\n");
i = saveSP+1;
s = (nargs==1) ? 1 : tonumber(Stack[i++], "/");
for (; i < (int)SP; i++) {
n = tonumber(Stack[i], "/");
if (n == 0)
lerror("/: error: division by zero\n");
s /= n;
}
v = number(s);
break;
case F_LT:
argcount("<", nargs, 2);
if (tonumber(Stack[SP-2],"<") < tonumber(Stack[SP-1],"<"))
v = T;
else
v = NIL;
break;
case F_NOT:
argcount("not", nargs, 1);
v = ((Stack[SP-1] == NIL) ? T : NIL);
break;
case F_EVAL:
argcount("eval", nargs, 1);
v = eval(Stack[SP-1], &NIL);
break;
case F_PRINT:
for (i=saveSP+1; i < (int)SP; i++)
print(stdout, v=Stack[i]);
break;
case F_READ:
argcount("read", nargs, 0);
v = read_sexpr(stdin);
break;
case F_LOAD:
argcount("load", nargs, 1);
v = load_file(tosymbol(Stack[SP-1], "load")->name);
break;
case F_PROG1:
// return first arg
if (nargs < 1)
lerror("prog1: error: too few arguments\n");
v = Stack[saveSP+1];
break;
case F_APPLY:
// unpack a list onto the stack
argcount("apply", nargs, 2);
v = Stack[saveSP] = Stack[SP-1]; // second arg is new arglist
f = Stack[SP-2]; // first arg is new function
POPN(2); // pop apply's args
if (isbuiltin(f)) {
if (isspecial(f))
lerror("apply: error: cannot apply special operator "
"%s\n", builtin_names[intval(f)]);
while (iscons(v)) {
PUSH(car_(v));
v = cdr_(v);
}
goto apply_builtin;
}
noeval = 1;
goto apply_lambda;
}
SP = saveSP;
return v;
}
else {
v = Stack[saveSP] = cdr_(Stack[saveSP]);
}
apply_lambda:
if (iscons(f)) {
headsym = car_(f);
if (headsym == LABEL) {
// (label name (lambda ...)) behaves the same as the lambda
// alone, except with name bound to the whole label expression
labl = f;
f = car(cdr(cdr_(labl)));
headsym = car(f);
}
// apply lambda or macro expression
PUSH(cdr(cdr(cdr_(f))));
lenv = &Stack[SP-1];
PUSH(car_(cdr_(f)));
argsyms = &Stack[SP-1];
PUSH(car_(cdr_(cdr_(f))));
body = &Stack[SP-1];
if (labl) {
// add label binding to environment
PUSH(labl);
PUSH(car_(cdr_(labl)));
*lenv = cons_(cons(&Stack[SP-1], &Stack[SP-2]), lenv);
POPN(3);
v = Stack[saveSP]; // refetch arglist
}
if (headsym == MACRO)
noeval = 1;
else if (headsym != LAMBDA)
lerror("apply: error: head must be lambda, macro, or label\n");
// build a calling environment for the lambda
// the environment is the argument binds on top of the captured
// environment
while (iscons(v)) {
// bind args
if (!iscons(*argsyms)) {
if (*argsyms == NIL)
lerror("apply: error: too many arguments\n");
break;
}
asym = car_(*argsyms);
if (!issymbol(asym))
lerror("apply: error: formal argument not a symbol\n");
v = car_(v);
if (!noeval) v = eval(v, penv);
PUSH(v);
*lenv = cons_(cons(&asym, &Stack[SP-1]), lenv);
POPN(2);
*argsyms = cdr_(*argsyms);
v = Stack[saveSP] = cdr_(Stack[saveSP]);
}
if (*argsyms != NIL) {
if (issymbol(*argsyms)) {
if (noeval) {
*lenv = cons_(cons(argsyms, &Stack[saveSP]), lenv);
}
else {
PUSH(NIL);
PUSH(NIL);
rest = &Stack[SP-1];
// build list of rest arguments
// we have to build it forwards, which is tricky
while (iscons(v)) {
v = eval(car_(v), penv);
PUSH(v);
v = cons_(&Stack[SP-1], &NIL);
POP();
if (iscons(*rest))
cdr_(*rest) = v;
else
Stack[SP-2] = v;
*rest = v;
v = Stack[saveSP] = cdr_(Stack[saveSP]);
}
*lenv = cons_(cons(argsyms, &Stack[SP-2]), lenv);
}
}
else if (iscons(*argsyms)) {
lerror("apply: error: too few arguments\n");
}
}
SP = saveSP; // free temporary stack space
PUSH(*lenv); // preserve environment on stack
lenv = &Stack[SP-1];
v = eval(*body, lenv);
POP();
// macro: evaluate expansion in the calling environment
if (headsym == MACRO)
return eval(v, penv);
return v;
}
type_error("apply", "function", f);
return NIL;
}