bug: Assign of consumable to variable should call (like an expression)

[phorward]

Given tokay -- hello1234

Tokay 0.6.4
>>> x = Int
>>> x
1234
>>> X : @{ x = Int x }
Line 1, column 1: Cannot assign to constant 'X', because it must be consumable. Use an identifier starting in lower-case, e.g. 'x'
>>> 

Inside of the parselet definition, the assignment of Int to x should call Int. It can be worked around by X : @{ x = {Int} x }.