Oversaturated Calls in Currying

[iamrecursion]

Summary

While support for currying has been implemented to comply with luna/enso#18, it currently doesn't handle the case where a function is applied to more arguments than it takes on its own. This isn't intuitively an issue, but becomes one when functions can return functions, to which the remaining arguments should be applied.

Value

Implementing this will complete Enso's support for curried function application, and hence complete the set of tasks required to support the proper language semantics for function calls.

Specification

• It is not (statically) an error to apply a function to more arguments than it is defined for.
• Functions applied to a number of arguments greater than their arity are evaluated, and then the remaining arguments are applied to the returned callable. If the evaluated function does not return a callable, this is then an error.
• Any overflowing default ignore arguments (x=!!, for example) should be retained and should be applied to a returned function. If the returned function has no argument by that name, then it becomes an error as long as that argument would be applied to it.

Acceptance Criteria & Test Cases

• The above specification has been implemented and tested.
• The implementation of this feature does not result in any performance regressions.

[iamrecursion]

Some notes on the proposed implementation:

• Curried functions need to know if they are oversaturated. Look at the function schema (ArgumentSchema). It should have an array with the oversaturated arguments as CallArgumentInfo.
• Push the CallOptimiserNode down into CachedArgumentSorterNode, as well as the corresponding logic.
• Inside the cached sorter, delegate back to the ArgumentSorterNode, with a schema containing just the oversaturated arguments.
• Then in execute in cached, we can (in the oversaturated case) execute on the child sorter.
• Function itself will need an additional array to track the oversaturated arguments, initialized to null.
• The argument sorter will return two arrays, via an optimised pair type.