Hi, I'm writing a function to recursively traverse a heterogeneous tree of
immutables and replace certain elements of it. So far I have:
subst(x::Number, assoc::Associative) = x
subst(x::Variable, assoc::Associative) = get(assoc, x, x)
subst{T}(x::T, assoc::Associative) = T([subst(getfield(x, f), assoc) for f
in fieldnames(x)]...)
I.e. numbers are kept as is, variables are possible replaced, and composite
structures are recursively traversed. This doesn't look very
compiler-friendly, so question 1 is if there's a better way of writing
this, short of manually writing one `subst` for each type.
My problem is that the above fails when the composite structure is
parametric, since a Variable might be replaced by a number. Eg. `Pair(2,
Variable(:x))` will become `Pair(2, 5)`, and that's a different type, so
the T([ ]...) line fails because T is Pair{Int, Variable}.
Question 2 is: given T = Pair{Int, Int}, is there any way to recover Pair?
Pair{Int, Int}.name returns Pair, but as a TypeName.
Cédric
