Removing CST branch during visit - rascal

Question

I have a syntax containing this expression: {Binding ","}+
At some points, I would like to remove Binding based on their value. Is there a simple way of doing this inside a visit expression?

Answer 1

Yes, if you use concrete syntax matching, it will be something like the following:
In this case we are removing the last binding:
visit (myProgram) {
case (Expression) `let <{Binding ","}+ otherBindings>, <Binding myBinding> in <Expression e>`
=> (Expression) `let <{Binding ","}+ otherBindings> in <Expression e>`
}
You could also remove the first binding:
visit (myProgram) {
case (Expression) `let <Binding myBinding>, <{Binding ","}+ otherBindings> in <Expression e>`
=> (Expression) `let <{Binding ","}+ otherBindings> in <Expression e>`
}
I expect the pattern match for myBinding to have more details, or you have a when clause or something to decide if and when to remove the binding.
Or one in the middle:
visit (myProgram) {
case (Expression) `let <{Binding ","}+ firstThese>, <Binding myBinding>, <{Binding ","}+ thenOthers> in <Expression e>`
=> (Expression) `let <{Binding ","}+ firstThese>, <{Binding ","}+ theOthers> in <Expression e>`
}
Rascal takes care of removing the additional separator commas where necessary.
Note that all the types in the patterns will become optional in the near future, and you'd write:
{Binding ","}+ bs1, bs2;
Binding myBinding;
visit (myProgram) {
case (Expression) `let <bs1>, <myBinding>, <bs2> in <Expression e>`
=> (Expression) `let <bs1>, <bs2> in <Expression e>`
}