Support left and right (curried) positional arguments

[countvajhula]

This is a WIP PR to implement a possible way of addressing #134 , and needs input on whether it makes sense, is appropriate for inclusion in the arguments package, is a good solution, etc.

The essential change is to decompose positional arguments into two sets left and right, to be able to represent argument sets in curried functions.

• At the moment, it is fully backwards compatible and all the tests pass.
• There are no new docs or tests yet.
• An interesting consideration is how composition of argument sets should be defined. Formerly for argument structures a and b, we simply compose the positional lists in the order supplied. With both left- and right-handed positional arguments, we could naively do left(a) ++ left(b) and right(a) ++ right(b), but somehow, it seems more correct to compose them as left(a) ++ left(b) and right(b) ++ right(a), i.e. with the order of composition reversed for the right-sided positional arguments. This seems to make sense if we treat the order of arguments provided to arguments-merge as "priority" of arguments. When we left-curry a function and provide additional arguments in sequence, each new argument takes up the left-most position not already claimed. Likewise with right-curry, each fresh argument takes up the right-most position not already claimed. It feels like argument composition ought to mirror this behavior, but I'm not sure. In any case that's the composition strategy in this PR at the moment.

[codecov[bot]]

Codecov Report

Merging #136 into master will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #136   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           18        18           
  Lines          846       846           
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  Hits           846       846           

Impacted Files	Coverage Δ
arguments/main.rkt	100.00% <100.00%> (ø)
mock/private/base.rkt	100.00% <0.00%> (ø)

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[countvajhula]

With the changes in this PR, the downstream module referenced in #134 would look like this: https://github.com/countvajhula/relation/commit/e1917f75308843bed81df09c0fa08f59eb96caa6

[countvajhula]

See discussion in #134