support display of arbitrary textual MIME types in REPL

[stevengj]

By default, the REPL displays objects in text/plain format, but if you explicitly call display("text/foo", x) then this PR allows it to print.

e.g. it was noted by @cstjean on discourse that the inability to do display("text/csv", matrix) was annoying. This now works.

Also as noted by @cstjean, the exception thrown by display("text/foo", x) was somewhat confusing if the problem is the lack of a show method for text/foo. After this PR, it throws the expected MethodError for show (rather than a MethodError for display).

[cstjean]

Thanks!

By default, the REPL displays objects in text/plain format

Interestingly, display("text/plain", rand(40, 2)) prints the whole array in IJulia, but it gets abridged at the REPL. If that's not the proper way of displaying the whole array, what is? "text/csv"? writedlm?

[stevengj]

show(STDOUT, "text/plain", x) will do it.

Seems like we should support a 2-arg version show("text/plain", x) via

show(m::MIME, x) = show(STDOUT, m, x)
show(m::AbstractString, x) = show(MIME(m), x)

[stevengj]

(I fixed the IJulia inconsistency in JuliaLang/IJulia.jl@8f92249, thanks.)

[stevengj]

Should be ready to merge.

[StefanKarpinski]

https://discourse.julialang.org/t/possibly-incorrect-displayable-text-html-in-v0-6/2145

[stevengj]

@StefanKarpinski, yes, I ran into this in JuliaPy/PyPlot.jl#281 as well. I'm thinking that maybe the REPL display should override displayable so that it only returns true for text/plain. If you explicitly call display("text/html", x) then it will still work (printing the HTML text), however.

[tlnagy]

So this change breaks Compose.jl on v0.6 since we depend on the @try_display macro.

import Base.Multimedia: @try_display, xdisplayable

function display(p::Context)
    displays = Base.Multimedia.displays
    for i = length(displays):-1:1
        m = default_mime()
        if xdisplayable(displays[i], m, p)
             @try_display return display(displays[i], m, p)
        end

        if xdisplayable(displays[i], p)
            @try_display return display(displays[i], p)
        end
    end
    invoke(display, Tuple{Any}, p)
end

https://github.com/GiovineItalia/Compose.jl/blob/master/src/Compose.jl#L227-L242

How to you recommend doing this with this change?

[stevengj]

@tlnagy, you shouldn't be overriding display in the first place. Override show.

The only reason to override display is if you are defining a new Display type, which is not the case in Compose.

[stevengj]

See http://docs.julialang.org/en/latest/manual/types.html#Custom-pretty-printing-1

[tlnagy]

I'm not sure why we have that in the Compose codebase. It looks like Daniel added that 3 years ago. I'll try and strip it out and see what happens.