In some circumstances, the column mini-language requires wrapping the argument in a 1-tuple

[s-leroux]

https://github.com/s-leroux/fin/blob/1d7dbf85eceb1bebb41be36195dc99180bff6fc7/examples/fin/model/warrant_price_change.py#L40

In some circumstances, the column mini-language requires wrapping the argument in a 1-tuple. This is confusing.

In practice, the following code is ambiguous:

(callable, callable, "X")

Using the infix notation, it can be parsed either as callable(callable(), "X") or callable(callable("X")) or even callable(callable()), "X".

[s-leroux]

The new interpreter introduced in 3161ebf3aff4cf23d8d29e0b31172c116205ddee is right-associative.

So (callable_1, callable_2, "X") is interpreted as (callable_1, (callable_2, "X")).

If callable_2 has to be interpreted as a nullary function, it requires explicit wrapping in a 1-tuple: (callable_1, (callable_2,), "X"). The error-prone part here is the trailing comma required by Python for 1-tuple.

• One solution would be allowing for wrapping expressions in other sequences, like lists:

  (callable_1, [callable_2], "X")

  I don't particularly like that solution. See #12 for another possible interpretation of the list literals.

• Another option would be to introduce a higher-order function to rewrite the expression:

  def singleton(fct):
    def _singleton(*args):
        return ((fct,),args)
    return _singleton
  
  (callable_1, singleton(callable_2), "X")

Closing as stale.