map over nested structures

[goretkin]

I'd like to write something concise to turn

[(1, 2), ((3, 4), (5, [7, 8]))]

into

[(1.0, 2.0), ((3.0, 4.0), (5.0, [7.0, 8.0]))]

If the structures are "uniformly" nested, one idea from @ssfrr is to e.g. define fmap(f) = x->map(f,x)
then

x = [(1,2), (3,4)]
fmap(fmap(Float64))(x)

You can then use whatever idiom for iterated functions to concisely write deeply but uniformly nested structures.

For non-uniformly nested structures, there's a question about how deep to apply the function. I'm not sure what a good generic API for what I want would be.

Related:
#32081 (comment)
#32796
#20502

[ghost]

ffmap(f, x::Int) = f(x)
ffmap(f, x::Union{Tuple, Array}) = map(y -> ffmap(f, y), x)

x = [(1, 2), ((3, 4), (5, [7, 8]))]
ffmap(Float64, x)

Like this?

[mcabbott]

Sounds like another reason to want #24990, with which you could write map(map(f, _), xs), I think.

[brenhinkeller]

Between the suggestion above and the zillion underscore proposals and PRs out there, I think we can close this but feel free to undo if anyone disagrees!

[aplavin]

See Accessors.jl as well: their modify(f, obj, optic) is basically this arbitrarily-nested map.