Customized printing for Struct within Expr

Internals & Design
1

For Grassmann.jl, I would like to customize the printing similar to the Complex numbers. Consider:

julia> using Grassmann

julia> @basis tangent(ℝ^2,2,2) # 2D Grade, 2nd Order, 2 Variables
(⟨++₁₂⟩, v, v₁, v₂, ∂₁, ∂₂, v₁₂, ∂₁v₁, ∂₂v₁, ∂₁v₂, ∂₂v₂, ∂₁₂, ∂₁v₁₂, ∂₂v₁₂, ∂₁₂v₁, ∂₁₂v₂, ∂₁₂v₁₂)

julia> ∇ = ∂1v1 + ∂2v2
0v₁₂ + 1∂₁v₁ + 0∂₂v₁ + 0∂₁v₂ + 1∂₂v₂ + 0∂₁₂

julia> Expr(:call,:/,1,∇⋅∇)
:(1 / 0.0v₁ + 0.0v₂ + 1∂₁∂₁ + 1∂₂∂₂)

The problem is that when I embed my number in an Expr there is ambiguity due to missing parenthesis.

julia> z = 1+im
1 + 1im

julia> Expr(:call,:/,1,z)
:(1 / (1 + 1im))

For Complex numbers this is resolved by adding extra (...) parenthesis around the printed value.

How can I customize the printing so that my numbers are also parenthesized in an Expr like this?

2

You can have a look at how it’s defined for Base.Complex with @edit show(stdin, 1.0im). It looks like you just need to overload Base.show_unquoted. (In the lines below)

3 
julia> Base.show_unquoted(stdout,1+im)
1 + 1im

this does not seem to reproduce the print behavior I am after, it should be (1 + 1im) instead

4

You need to pass the outer operator precedence as well.

1 Like
5

This works:

julia> Base.show_unquoted(stdin, 1.0im, 0#=Don't know what this does, but it isn't used by Complex=#, Base.operator_precedence(:*))
(0.0 + 1.0im)
6

This new definition does what I need, which will go into the AbstractTensors.jl package

function Base.show_unquoted(io::IO, z::T, ::Int, prec::Int) where T<:TensorAlgebra
    if T<:TensorMixed && Base.operator_precedence(:+) <= prec
        print(io, "(")
        show(io, z)
        print(io, ")")
    else
        show(io, z)
    end
end