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module src.primitives.conditional;
import std.variant;
import std.typecons;
import std.container : DList;
import src.stack;
Nullable!(DList!Token) buffer;
bool concluded = true;
bool drop_mode = false;
void capture(Token token) {
if ( !drop_mode ) {
buffer.insertBack(token);
}
}
bool drop(Token token) {
if ( concluded && buffer.isNull ) {
return false;
}
if ( token.type == typeid(string) ) {
switch ( *token.peek!string ) {
case "if" : eval_if; break;
case "then" : eval_then; break;
case "else" : eval_else; break;
default : capture(token); break;
}
} else {
capture(token);
}
return true;
}
void eval_if() {
if ( concluded ) {
buffer = DList!Token();
drop_mode = !stack.pop.get!bool;
concluded = false;
} else {
throw new Exception("conditionals may not be nested directly");
}
}
void eval_then() {
if ( concluded ) {
throw new Exception("`then` without preceding `if`");
} else {
drop_mode = !drop_mode;
}
}
void eval_else() {
if ( concluded ) {
throw new Exception("`else` without preceding `if`");
} else {
drop_mode = false;
concluded = true;
}
}
bool dischargeable() {
return concluded && !buffer.isNull;
}
Stack!Token discharge() {
if ( concluded ) {
Stack!Token result = buffer[];
buffer.nullify;
return result;
} else {
throw new Exception("unconcluded conditional may not be discharged");
}
}
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