Add dhall --type option.

[sellout]

In psibi/dhall-mode#7, I’ve made it possible to display the type of the file in the header line in Emacs. Currently I do

dhall --plain <<< $file 2>&1 >/dev/null

to capture the type, but I think that also does a bunch of other normalization work that I’m throwing away. It’d be great if it were possible to only do what’s necessary to get the type out, and to make it a bit less complicated to do so – ideally outputting the type on stdout, and the errors remaining on stderr.

[Gabriella439]

Yeah, I've been meaning to add optional sub-commands to Dhall to capture individual phases of the pipeline (i.e. dhall type, dhall normalize, dhall resolve, etc.). I'll take a stab at this

[Gabriella439]

There is one subtlety here: splitting out each phase of the interpreter into a separate subcommand would mean that you would need to do:

dhall resolve | dhall type

... if you want to get both import resolution and type-checking

[sellout]

For my own use case, I’m fine with that, as I want to basically show a one-line “sketch” of the type while editing, so avoiding resolution and normalization can often help with that.