Cannot parse optic _ && true

[jariji]

julia> @o (_ && true)
ERROR: LoadError: ArgumentError: Cannot parse optic _ && true. Lens expressions must start with _, got $(Expr(:escape, :(_ && true))) instead.

What's happening here?

[jw3126]

Note that it works with &:

julia> using Accessors

julia> @o _ & true
(::Base.Fix2{typeof(&), Bool}) (generic function with 1 method)

On the other hand && is not a function, but has special short-circuit semantics.

julia> dump(:(_ && true))
Expr
  head: Symbol &&
  args: Array{Any}((2,))
    1: Symbol _
    2: Bool true

julia> dump(:(_ & true))
Expr
  head: Symbol call
  args: Array{Any}((3,))
    1: Symbol &
    2: Symbol _
    3: Bool true

I think we could in improve the error message, but I don't think we should produce an optic from this.

[aplavin]

Btw, this kind of stuff works with AccessorsExtra – not with constants like true but with actual functions on each side:

julia> using AccessorsExtra

julia> @o _.a && _.b
(@o _.a) ⩓ (@o _.b)