On 03/22/2012 08:12 PM, F i L wrote:
Timon Gehr wrote:
I think that would necessitate the addition of AST macros.
You mean passing DMD's actual AST tree object? Only a stripped down
version?
We have the macro keyword. I envision something like:
macro replaceAggregate(macro newAggregate, macro loop : foreach(x;
aggr){statements}, macro x, macro aggr, macro statements) {
foreach(x; newAggregate){statements}
}
void main(){
int[] a = [1,2,3];
int[] b = [2,3,4];
replaceAggregate(b, foreach(x;a){writeln(x);});
}
(The syntax looks horrible, but you get the idea: AST walking by pattern
matching)
Ideally, such macros would allow introducing local helper variables
inside the macro that are not accessible from outside and introducing
variables/enums in the context the macro is used. (prefixing identifiers
that should interfere with the enclosing context with $ would be an
option). Another idea:
macro someFancyDSL(string dsl){
mixin(someFancyDSLtoD(dsl);
}
void main(){
int n = 5;
someFancyDSL {
import n;
let x = 1 : x
let y = product (take n) x
export y;
}
writeln(y);
}
// this would also enable less fancy but useful stuff:
macro until(macro condition, string str){
while(!condition){
mixin(str); // string and mixin not strictly necessary,
// maybe enable the feature on macro params too
}
}
void main(){
bool done = false;
int x;
until(done){
done = foo(x++);
}
}
This is just a very rough sketch though, we would need a much more
refined design. I think getting the symbol scoping right is most important.
