Add new dhall to-directory-tree command

[Gabriella439]

Fixes #1605

This command lets you transform Text literals into files and record literals
into directories.

[sjakobi]

Nice! This looks really handy! :)

The command name filesystem reminds me more of NTFS and Ext4 than directory trees. I don't have a great idea for a better name though… Something like directory-tree, generate-directory-tree, gen-dir-tree, dir-tree?!

Also: should this check whether the output directory is empty and abort otherwise? (Overridable with --force or so?). But that's something that could easily be added later on.

[Gabriella439]

@sjakobi: How about to-path? Then at some point we could also have a from-path subcommand that turns a directory tree into a Dhall expression

[Gabriella439]

@sjakobi: Or maybe to-tree / from-tree

[sjakobi]

@sjakobi: Or maybe to-tree / from-tree

to-tree is pretty good, although some notion of files would be nice to have in the name IMHO. to-dir-tree maybe?

[Gabriella439]

@sjakobi: Then maybe to-directory-tree (mainly to use complete words)

[sjakobi]

@sjakobi: Then maybe to-directory-tree (mainly to use complete words)

That's also fine, but remember that we already have dhall repl and dhall diff. ;)

[ari-becker]

@Gabriel439 some input - a dhall-to-directory-tree command would be massively more useful if, instead of requiring values to be Text, they could be Optional Text, and if the value is None Text then not to create the file. Sort of like how dhall-to-json will omit fields whose values are None Foo if --omitNull is set.

This would make it possible to generate different files on the basis of different inputs, rather than being restricted to generating a fixed set of files.

[Profpatsch]

Great! I’ve been wanting to have/write something like this in nix for a while, but now I can just do it from dhall directly.

[samuela]

is there an example of how to use this feature?

[mmhat]

@samuela There are some examples in the Haddock documentation here and there are also some tests covering the more elaborate fixpoint encoding of a directory tree in the testsuite of the dhall package here. Hope that helps.