move the docstrings

Author: mcabbott

src/Functors.jl

@@ -5,4 +5,260 @@ export @functor, @flexiblefunctor, fmap, fmapstructure, fcollect
 include("functor.jl")
 include("base.jl")
 
+"""
+    Functors.functor(x) = functor(typeof(x), x)
+
+Returns a tuple containing, first, a `NamedTuple` of the children of `x`
+(typically its fields), and second, a reconstruction funciton.
+This controls the behaviour of [`fmap`](@ref).
+
+Methods should be added to `functor(::Type{T}, x)` for custom types,
+usually using the macro [@functor](@ref).
+"""
+functor
+
+"""
+    @functor T
+    @functor T (x,)
+
+Adds methods to [`functor`](@ref) allowing recursion into objects of type `T`,
+and reconstruction. Assumes that `T` has a constructor accepting all of its fields,
+which is true unless you have provided an inner constructor which does not.
+
+By default all fields of `T` are considered [children](@ref); 
+this can be restricted be restructed by providing a tuple of field names.
+
+# Examples
+```jldoctest
+julia> struct Foo; x; y; end
+
+julia> @functor Foo
+
+julia> Functors.children(Foo(1,2))
+(x = 1, y = 2)
+
+julia> _, re = Functors.functor(Foo(1,2));
+
+julia> re((10, 20))
+Foo(10, 20)
+
+julia> struct TwoThirds a; b; c; end
+
+julia> @functor TwoThirds (a, c)
+
+julia> ch2, re3 = Functors.functor(TwoThirds(10,20,30));
+
+julia> ch2
+(a = 10, c = 30)
+
+julia> re3(("ten", "thirty"))
+TwoThirds("ten", 20, "thirty")
+
+julia> fmap(x -> 10x, TwoThirds(Foo(1,2), Foo(3,4), 56))
+TwoThirds(Foo(10, 20), Foo(3, 4), 560)
+```
+"""
+var"@functor"
+
+"""
+    Functors.isleaf(x)
+
+Return true if `x` has no [`children`](@ref) according to [`functor`](@ref).
+
+# Examples
+```jldoctest
+julia> Functors.isleaf(1)
+true
+
+julia> Functors.isleaf([2, 3, 4])
+true
+
+julia> Functors.isleaf(["five", [6, 7]])
+false
+
+julia> Functors.isleaf([])
+false
+
+julia> Functors.isleaf((8, 9))
+false
+
+julia> Functors.isleaf(())
+true
+```
+"""
+isleaf
+
+"""
+    Functors.children(x)
+
+Return the children of `x` as defined by [`functor`](@ref).
+Equivalent to `functor(x)[1]`.
+"""
+children
+
+"""
+    fmap(f, x; exclude = Functors.isleaf, walk = Functors._default_walk)
+
+A structure and type preserving `map`.
+
+By default it transforms every leaf node (identified by `exclude`, default [`isleaf`](@ref))
+by applying `f`, and otherwise traverses `x` recursively using [`functor`](@ref).
+
+# Examples
+```jldoctest
+julia> fmap(string, (x=1, y=(2, 3)))
+(x = "1", y = ("2", "3"))
+
+julia> nt = (a = [1,2], b = [23, (45,), (x=6//7, y=())], c = [8,9]);
+
+julia> fmap(println, nt)
+[1, 2]
+23
+45
+6//7
+()
+[8, 9]
+(a = nothing, b = Any[nothing, (nothing,), (x = nothing, y = nothing)], c = nothing)
+
+julia> fmap(println, nt; exclude = x -> x isa Array)
+[1, 2]
+Any[23, (45,), (x = 6//7, y = ())]
+[8, 9]
+(a = nothing, b = nothing, c = nothing)
+
+julia> twice = [1, 2];
+
+julia> fmap(println, (i = twice, ii = 34, iii = [5, 6], iv = (twice, 34), v = 34.0))
+[1, 2]
+34
+[5, 6]
+34.0
+(i = nothing, ii = nothing, iii = nothing, iv = (nothing, nothing), v = nothing)
+```
+
+If the same node (same according to `===`) appears more than once,
+it will only be handled once, and only be transformed once with `f`.
+Thus the result will also have this relationship.
+
+By default, `Tuple`s, `NamedTuple`s, and some other container-like types in Base have
+children to recurse into. Arrays of numbers do not.
+To enable recursion into new types, you must provide a method of [`functor`](@ref),
+which can be done using the macro [`@functor`](@ref):
+
+```jldoctest withfoo
+julia> struct Foo; x; y; end
+
+julia> @functor Foo
+
+julia> struct Bar; x; end
+
+julia> @functor Bar
+
+julia> m = Foo(Bar([1,2,3]), (4, 5, Bar(Foo(6, 7))));
+
+julia> fmap(x -> 10x, m)
+Foo(Bar([10, 20, 30]), (40, 50, Bar(Foo(60, 70))))
+
+julia> fmap(string, m)
+Foo(Bar("[1, 2, 3]"), ("4", "5", Bar(Foo("6", "7"))))
+
+julia> fmap(string, m, exclude = v -> v isa Bar)
+Foo("Bar([1, 2, 3])", (4, 5, "Bar(Foo(6, 7))"))
+```
+
+To recurse into custom types without reconstructing them afterwards,
+use [`fmapstructure`](@ref).
+
+For advanced customization of the traversal behaviour, pass a custom `walk` function of the form `(f', xs) -> ...`.
+This function walks (maps) over `xs` calling the continuation `f'` to continue traversal.
+
+```jldoctest withfoo
+julia> fmap(x -> 10x, m, walk=(f, x) -> x isa Bar ? x : Functors._default_walk(f, x))
+Foo(Bar([1, 2, 3]), (40, 50, Bar(Foo(6, 7))))
+```
+"""
+fmap
+
+"""
+    fmapstructure(f, x; exclude = isleaf)
+
+Like [`fmap`](@ref), but doesn't preserve the type of custom structs.
+Instead, it returns a `NamedTuple` (or a `Tuple`, or an array),
+or a nested set of these.
+
+Useful for when the output must not contain custom structs.
+
+# Examples
+```jldoctest
+julia> struct Foo; x; y; end
+
+julia> @functor Foo
+
+julia> m = Foo([1,2,3], [4, (5, 6), Foo(7, 8)]);
+
+julia> fmapstructure(x -> 2x, m)
+(x = [2, 4, 6], y = Any[8, (10, 12), (x = 14, y = 16)])
+
+julia> fmapstructure(println, m)
+[1, 2, 3]
+4
+5
+6
+7
+8
+(x = nothing, y = Any[nothing, (nothing, nothing), (x = nothing, y = nothing)])
+```
+"""
+fmapstructure
+
+"""
+    fcollect(x; exclude = v -> false)
+
+Traverse `x` by recursing each child of `x` as defined by [`functor`](@ref)
+and collecting the results into a flat array, ordered by a breadth-first
+traversal of `x`, respecting the iteration order of `children` calls.
+
+Doesn't recurse inside branches rooted at nodes `v`
+for which `exclude(v) == true`.
+In such cases, the root `v` is also excluded from the result.
+By default, `exclude` always yields `false`.
+
+See also [`children`](@ref).
+
+# Examples
+
+```jldoctest
+julia> struct Foo; x; y; end
+
+julia> @functor Foo
+
+julia> struct Bar; x; end
+
+julia> @functor Bar
+
+julia> struct NoChildren; x; y; end
+
+julia> m = Foo(Bar([1,2,3]), NoChildren(:a, :b))
+Foo(Bar([1, 2, 3]), NoChildren(:a, :b))
+
+julia> fcollect(m)
+4-element Vector{Any}:
+ Foo(Bar([1, 2, 3]), NoChildren(:a, :b))
+ Bar([1, 2, 3])
+ [1, 2, 3]
+ NoChildren(:a, :b)
+
+julia> fcollect(m, exclude = v -> v isa Bar)
+2-element Vector{Any}:
+ Foo(Bar([1, 2, 3]), NoChildren(:a, :b))
+ NoChildren(:a, :b)
+
+julia> fcollect(m, exclude = v -> Functors.isleaf(v))
+2-element Vector{Any}:
+ Foo(Bar([1, 2, 3]), NoChildren(:a, :b))
+ Bar([1, 2, 3])
+```
+"""
+fcollect
+
 end # module