added (if-some)

tk/listlogic.scm

@@ -2,7 +2,7 @@
   #:export (flatten
             lp&
             l&
-            )
+            if-some)
   #:duplicates (warn-override-core warn ))
 
 (define (flatten-helper lst acc stk)
@@ -37,8 +37,7 @@
            '())
           ((p (car ls1) (car ls2))
            (cons (car ls1) (loop (cdr ls1) (cdr ls2))))
-          (else '())
+          (else '()))))
-          )))
 
 ;; Collect entries from the beginning of the given lists as long as those
 ;;entries are equivalent according to (eqv?)
@@ -46,3 +45,6 @@
   (cond ((eqv? ls1 ls2) ls1)
         (else (lp& eqv? ls1 ls2))))
 
+;; Returns the argument if it isn't #f, otherwise returns the empty list
+(define (if-some $cond)
+  (if $cond $cond '()))