+;; the if* macro used in Allegro:
+;;
+;; This is in the public domain... please feel free to put this definition
+;; in your code or distribute it with your version of lisp.
+
+(in-package #:kmrcl)
+
+(eval-when (:compile-toplevel :load-toplevel :execute)
+ (defvar if*-keyword-list '("then" "thenret" "else" "elseif")))
+
+(defmacro if* (&rest args)
+ (do ((xx (reverse args) (cdr xx))
+ (state :init)
+ (elseseen nil)
+ (totalcol nil)
+ (lookat nil nil)
+ (col nil))
+ ((null xx)
+ (cond ((eq state :compl)
+ `(cond ,@totalcol))
+ (t (error "if*: illegal form ~s" args))))
+ (cond ((and (symbolp (car xx))
+ (member (symbol-name (car xx))
+ if*-keyword-list
+ :test #'string-equal))
+ (setq lookat (symbol-name (car xx)))))
+
+ (cond ((eq state :init)
+ (cond (lookat (cond ((string-equal lookat "thenret")
+ (setq col nil
+ state :then))
+ (t (error
+ "if*: bad keyword ~a" lookat))))
+ (t (setq state :col
+ col nil)
+ (push (car xx) col))))
+ ((eq state :col)
+ (cond (lookat
+ (cond ((string-equal lookat "else")
+ (cond (elseseen
+ (error
+ "if*: multiples elses")))
+ (setq elseseen t)
+ (setq state :init)
+ (push `(t ,@col) totalcol))
+ ((string-equal lookat "then")
+ (setq state :then))
+ (t (error "if*: bad keyword ~s"
+ lookat))))
+ (t (push (car xx) col))))
+ ((eq state :then)
+ (cond (lookat
+ (error
+ "if*: keyword ~s at the wrong place " (car xx)))
+ (t (setq state :compl)
+ (push `(,(car xx) ,@col) totalcol))))
+ ((eq state :compl)
+ (cond ((not (string-equal lookat "elseif"))
+ (error "if*: missing elseif clause ")))
+ (setq state :init)))))
+