Command argument splatting

[Isaac Elliott]

let x = ["a", "b"] in
`echo $..x`

~> 

`echo a b`

(\x -> `echo $..x`) : Array String -> Cmd

• Implementation
• Documentation
  • Feature
  • Grammar

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As part of #138, I changed command argument interpolation to use the same rules as string interpolation.

Variable interpolation in commands used to choose between expanding to a single argument or multiple arguments based on the variable's type:

(\x -> `echo $x`) : ToArgs a=> a -> Cmd

Interpolating an Array String would expand to multiple arguments:

let x = ["a", "b"] in
`echo $x`

~>

`echo a b`

Since #138, you can't interpolate variables of type Array String into commands. Only Strings:

(\x -> `echo $x`) : String -> Cmd

I mostly did this by accident; my intent was to simplify the implementation of command syntax. I then realised that the explicitness of the approach could be helpful.

Should the result of

let x = ["a", "b"] in
`echo $x`

be

`echo a b`

or

`echo "a b"`

or

`echo "[\"a\", \"b\"]"`

or something else?

Some of the options are more sensible than others, but the fact that I can ask the question also seems like a problem in itself.

When Array String can be substituted using $,

`echo $x`

and

`echo "$x"`

can mean different things. If x : Array String, then adding the double quotes changes the meaning of the command. I think it would be good if adding double quotes like this was always redundant, rather than "only being redundant when x : String". Substituting String and Array String with $ reminds me a bit too much of current shells, in which shellcheck recommends always quoting substitutions to avoid weirdness. ipso doesn't have that weirdness, but I think it'll be nice to move in the other direction.