`if` is for getting a value, not nec. side-effecty

Since `if` is more of an expression (rather than executed for side-effects), removed the "do-".

Since `when` supplies an implicit `do`, left the "do-", but removed the "else" (given the implicit `do`).
Merge pull request #26 from uvtc/patch-3

`if` is for getting a value, not nec. side-effecty