Fix moving up and down in REPL

[huangyxi]

Fix #349 corresponding to JuliaLang/julia#54674

https://github.com/JuliaLang/julia/pull/54674/files#diff-730f90e0bf9ca018477a1d4a52e0d7398af2bb8cf9e401568fd86690eec81bb7L1453-R1488

[IanButterworth]

This seems brittle. Better to find first?

[huangyxi]

Thanks. I have improved the implementation by using findfirst. (8b6dc6f)

[IanButterworth]

Suggested change

	php_idx = findfirst(isa.(interface_modes, LineEdit.PrefixHistoryPrompt))
	php_idx = findfirst(isa(LineEdit.PrefixHistoryPrompt), interface_modes)

Avoid allocating

[huangyxi]

Currently, isa requires two arguments explicitly. Here is a workaround:

findfirst(Base.Fix2(isa, LineEdit.PrefixHistoryPrompt), interface_modes)

However, I'm uncertain about using Base.Fix2 since it hasn't been exported.

[IanButterworth]

Good point. It's fine to use Fix2, it's public, just not exported https://docs.julialang.org/en/v1/base/base/#Base.Fix2

[IanButterworth]

Seems good to me. Assuming the main mode is first is probably ok

[daviehh]

Thanks for the quick fix! If you do not wish to hard code by assuming main mode is first entry, one can replace the main_mode = interface_modes[1] line w/ something like

get_prompt_str = m -> LineEdit.prompt_string(isdefined(m, :prompt) ? m.prompt : "")
mm_idx_ = findfirst(m -> get_prompt_str(m) == REPL.JULIA_PROMPT, interface_modes) # main mode index
mm_idx = isnothing(mm_idx_) ? 1 : mm_idx_
main_mode = interface_modes[mm_idx]