No Exception when left associative single operand operator is in wrong position

[fasseg]

The following expression gets evaluated although the factorial is in a nonsensical position:

new ExpressionBuilder("3-!2")
    .operator(factorial)
    .build()
    .evaluate()

This should throw an exception

[dktcoding]

Given that operator association doesn't mean operator position, that expression is actually valid, maybe it's possible to add an "operator position" flag but it will actually create a fairly complex code for some really weird corner cases...

Question: Is there other "just unary" operator that uses postfix notation in an infix environment? (aside from factorial)

Currently unary operators like - and + don't fail because the tokenizer attempts to retrieve the binary operator, but if you comment lines 96, 97, 98 and 100 of Operators.class, an expression like 3- becomes -3.

Since I honestly can't think/find another operator that behaves like factorial, IMHO the simplest solution is to add ! as a builtin operator and special case it (for instance treat it like a binary operator, and insert an unused value as the second argument).

The only issue I can see (besides having an unused token) is that implicit multiplication operator won't be added (but actually fails now too).

[fasseg]

Hmmm, I will have a think about that. I'm not in favour of adding it as a builtin operator and have some special handling for that, since it could happen with any user-defined unary operator.