Fix gitignore and add truthiness transformer

.gitignore

@@ -1,5 +1,7 @@
-*\compiled\*
-*\*.bak
-*\*.html
-*\*.css
-*\*.js
+**/compiled/*
+**.bak
+**.html
+**.css
+**.js
+**.1
+**.2

predicates/logic.rkt

@@ -3,6 +3,7 @@
 (require "contract-helpers.rkt")
 
 (provide (contract-out [true? predicate/c]
+                       [without-truthiness (-> procedure? procedure?)]
                        [and? predicate*->/c]
                        [or? predicate*->/c]
                        [not? predicate->/c]
@@ -46,3 +47,12 @@
   (check-true (first-num-or-second-sym? 4 'baz))
   (check-false (first-num-or-second-sym? "smurf" '())))
 
+;; Helper for dealing with truthy predicates
+
+(define (without-truthiness f)
+  (compose true? f))
+
+(module+ test
+  (define member? (without-truthiness member))
+  (check-true (member? 'a '(a b c)))
+  (check-false (member? 1 '(a b c))))

predicates/predicates.scrbl

@@ -372,6 +372,17 @@ source code: @url["https://github.com/jackfirth/predicates"]
     (true? 'foo)
     ]}
 
+@defproc[(without-truthiness [f proc?]) proc?]{
+  Returns a procedure that's like @racket[f], but returns either @racket[#t] or
+  @racket[#f] based on whether @racket[f] returns false. Essentially, this procedure
+  turns functions that rely on returning "truthy" values into function that only
+  return a boolean.
+  @module-examples[
+    (define member? (without-truthiness member))
+    (member? 1 '(1 2 3))
+    (member? 'foo '(1 2 3))
+]}
+
 @defproc[(in-range? [low real?] [high real?] [exclusive? boolean? #f]) (-> any? boolean?)]{
   Returns a predicate that determins in its input is a real number between @racket[low]
   and @racket[high]. If @racket[exclusive?] is @racket[#t], then values @racket[=] to