double prim(bool get) {
if (get) ts.get();
switch (ts.current().kind) {
case Kind::number:
{
double v = ts.current().number_value;
ts.get();
return v;
}
case Kind::name:
{
double &v = table[ts.current().string_value];
if (ts.get().kind == Kind::assign) v = expr(true);
return v;
}
case Kind::minus:
{
return -prim(true);
}
case Kind::lp:
{
auto e = expr(true);
if (ts.current().kind != Kind::rp)
return error("'(' expected");
}
default:
return error("primary expected");
}
}
void calculate() {
table["pi"] = 3.1415926535897932385;
table["e"] = 2.718281828459052354;
for (;;) {
ts.get();
if (ts.current().kind == Kind::end) break;
if (ts.current().kind == Kind::print) continue;
std::cout << expr(false) << std::endl;
}
}
double expr(bool get) {
double left = term(get);
for (;;) {
switch (ts.current().kind)
{
case Kind::plus:
left += term(true);
break;
case Kind::minus:
left -= term(true);
break;
default:
return left;
}
}
}
double term(bool get) {
double left = prim(get);
for (;;) {
switch (ts.current().kind) {
case Kind::mul:
left *= prim(true);
break;
case Kind::div:
if (auto d = prim(true)) {
left /= d;
break;
}
return error("divide by 0");
default:
return left;
}
}
}