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Comment by gjadi | Hacker News Reader

In Common Lisp, there is `unless' and `when' but they don't allow `else' branch.

(when CONDITION BODY)

(unless CONDITION BODY)

The value of the statement is BODY or NIL if it wasn't executed.

I can't remember a time when it wasn't clear (though you can always build usage that are unclear).

I think they mainly exist because `if' otherwise requires a `progn' if you want more than one expression in the true branch.

And using `cond' for 1 clause is a bit silly.

  (cond ((massivep building)
         (print-mass-warning building)
         (install-antigrav-module building)))