Function: if-let

if-let is a macro defined in subr.el.gz.

Signature

(if-let SPEC THEN &rest ELSE)

Documentation

Bind variables according to SPEC and evaluate THEN or ELSE.

Evaluate each binding in turn, as in let*, stopping if a binding value is nil. If all are non-nil return the value of THEN, otherwise the last form in ELSE.

Each element of SPEC is a list (SYMBOL VALUEFORM) that binds SYMBOL to the value of VALUEFORM. An element can additionally be of the form (VALUEFORM), which is evaluated and checked for nil; i.e. SYMBOL can be omitted if only the test result is of interest. It can also be of the form SYMBOL, then the binding of SYMBOL is checked for nil.

As a special case, interprets a SPEC of the form (SYMBOL SOMETHING) like ((SYMBOL SOMETHING)). This exists for backward compatibility with an old syntax that accepted only one binding.

View in manual

Probably introduced at or before Emacs version 25.1.

Source Code

;; Defined in /usr/src/emacs/lisp/subr.el.gz
(defmacro if-let (spec then &rest else)
  "Bind variables according to SPEC and evaluate THEN or ELSE.
Evaluate each binding in turn, as in `let*', stopping if a
binding value is nil.  If all are non-nil return the value of
THEN, otherwise the last form in ELSE.

Each element of SPEC is a list (SYMBOL VALUEFORM) that binds
SYMBOL to the value of VALUEFORM.  An element can additionally be
of the form (VALUEFORM), which is evaluated and checked for nil;
i.e. SYMBOL can be omitted if only the test result is of
interest.  It can also be of the form SYMBOL, then the binding of
SYMBOL is checked for nil.

As a special case, interprets a SPEC of the form \(SYMBOL SOMETHING)
like \((SYMBOL SOMETHING)).  This exists for backward compatibility
with an old syntax that accepted only one binding."
  (declare (indent 2)
           (debug ([&or (symbolp form)  ; must be first, Bug#48489
                        (&rest [&or symbolp (symbolp form) (form)])]
                   body)))
  (when (and (<= (length spec) 2)
             (not (listp (car spec))))
    ;; Adjust the single binding case
    (setq spec (list spec)))
  (list 'if-let* spec then (macroexp-progn else)))