Cannot rebind `before`

[leque]

In SATySFi, before is syntactically a binary-operator (See the parser's binop rule). We can define (before) as a function:

let (before) a b = 0

But the above definition is never used, because before is handled in the parser's nxbfr rule, not in the evaluator; let (before) a b = 0 in 42 + (() before 3) is evaluated to 45, not 42.

# And I'm always confused by the fact that SATySFi's before has a different type from the one of Standard ML's before, 'a * unit -> 'a. :)