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Mercurial > core / lisp/std/macs/control.lisp

changeset 698: 96958d3eb5b0
parent: 0e00dec3de03
author: Richard Westhaver <ellis@rwest.io>
date: Fri, 04 Oct 2024 22:04:59 -0400
permissions: -rw-r--r--
description: fixes 
     1 ;;; std/macs/control.lisp --- Control Flow Macros
     2 
     3 ;;
     4 
     5 ;;; Code:
     6 (in-package :std/macs)
     7 
     8 (defmacro xor (&rest datums)
     9   "Evaluates its arguments one at a time, from left to right. If more than one
    10 argument evaluates to a true value no further DATUMS are evaluated, and NIL is
    11 returned as both primary and secondary value. If exactly one argument
    12 evaluates to true, its value is returned as the primary value after all the
    13 arguments have been evaluated, and T is returned as the secondary value. If no
    14 arguments evaluate to true NIL is returned as primary, and T as secondary
    15 value."
    16   (with-gensyms (xor tmp true)
    17     `(let (,tmp ,true)
    18        (declare (ignorable ,tmp))
    19        (block ,xor
    20          ,@(mapcar (lambda (datum)
    21                      `(if (setf ,tmp ,datum)
    22                           (if ,true
    23                               (return-from ,xor (values nil nil))
    24                               (setf ,true ,tmp))))
    25                    datums)
    26          (return-from ,xor (values ,true t))))))