it.jl

struct It{F}
    f::F
end

const it = It(identity)

(i::It)(x) = getfield(i, :f)(x)

(i::It)(xs...) = getfield(i, :f)(xs)

Base.getproperty(i::It, name::Symbol) = getproperty.(i, name)

Base.getindex(i::It, key) = getindex.(i, key)

struct ItStyle <: Base.BroadcastStyle
end

Base.BroadcastStyle(::Type{<:It}) = ItStyle()

Base.BroadcastStyle(::ItStyle, ::Base.Broadcast.DefaultArrayStyle{0}) = ItStyle()

Base.broadcastable(i::It) = i

Base.Broadcast.instantiate(bc::Base.Broadcast.Broadcasted{ItStyle}) = bc

Base.copy(bc::Base.Broadcast.Broadcasted{ItStyle}) =
    It(x -> bc.f(((arg isa It) ? arg(x) : arg[] for arg in bc.args)...))

Base.filter(f) = xs -> filter(f, xs)

Base.map(f) = xs -> map(f, xs)

Base.foldl(f) = xs -> foldl(f, xs)

@show 1:10 |> filter(isodd.(it)) |> map(it .* 2) |> foldl(it[1] .+ it[2])
#-> 50

@show [(x = 10, y = 20), (x = 30, y = 20)] |> filter(it.x .> it.y) |> map(it.x .+ it.y) |> sum
#-> 50