Re: if-let/if-let*/and-let/..

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

>  (if-let* (x) "dogs" "cats") => "cats"

We could detect this case and signal an error during macro-expansion for
it (the special (VAR EXP) form should be (VAR EXP) and not just
`(VAR)`).

>  (if-let* (x (y 2)) "dogs" "cats") => (void-function y)

This is right.  If you presume that `if-let` only takes the same syntax
as `let`, then the above would be equivalent to 

    (if-let* ((x nil) (y 2)) "dogs" "cats")

which is just a complicated way to write

    "cats"

so it's rather unlikely that a user would write that on purpose.
It's much more likely that he meant

    (if-let* (x (y 2)) "dogs" "cats")

to be treated as

    (if-let* ((x (y 2))) "dogs" "cats")

which will indeed correctly give you the (void-function y).

>  (if-let* (x (y 1) (z 2)) "dogs" "cats") => "cats"

Same as the first case above, we could/should detect this case during
macro-expansion since this is not of the form (VAR EXP) but (VAR EXP EXP).


        Stefan