Membership expressions

[darrylabbate]

Currently, in is only supported in for loops. in can be added as an infix operator (membership, pattern matching, etc); valid in any expression. Support for not in would need to be implemented as well.

Precedence level should be lower than ~ and .. but higher than &&

[darrylabbate]

Type dispatch:

• If y in the expression x in y can be coerced to string, x in y should essentially be the inverse of pattern matching (i.e. y ~ x).
• If y is a table, x in y evaluates as true if the value x (not key) is somewhere in the table.
• If y is a range, assert x is an integer (or float equivalent) and falls in the range. I.e. x in a..b:c == $\lbrace x|x\in c\mathbb{Z}, a \leqslant x \leqslant b \rbrace$

For all other types, it should follow whatever rules the pattern matching operation enforces.

[darrylabbate]

Precedence level should be lower than ~ and .. but higher than &&

Not currently possible to be lower than .. but also higher than &&. Logical operators should probably be lowered s.t. a in b..c && x in y..z does what you'd expect. .. was originally given very low precedence since its only real uses were for loops and substring extraction.