Add "conjoin" from chicken scheme

d-.scm

@@ -12,6 +12,7 @@
    argmin
    iterate
    upply
+   conjoin
    distinct?
    generator
    macro-expand
@@ -69,18 +70,30 @@
 	  vals))
 
 (define (iterate n f v)
+  "Repeatedly call f on values returned from (f v)"
   (if (zero? n)
       v
       (iterate (1- n) f (f v))))
 
 (define (upply a b cmp . fs)
+  "U-shapped apply, apply fs to a and b as in compose, then apply cmp to both results"
   (let ([arm-f (apply compose fs)])
     (cmp (arm-f a) (arm-f b))))
 
+(define (conjoin . preds)
+  "Returns a procedure that applies each pred to a single value, and returns #t if all return a truthy value. With no preds returns a one arg function that always returns true"
+  (if (null? preds)
+      (lambda (x) #t)
+      (lambda (x)
+	(if ((car preds) x)
+	    ((apply conjoin (cdr preds)) x)
+	    #f))))
+
 (define (distinct? . a)
+  "Are all values distinct, as in equal?"
   (if (or (null? a) (null? (cdr a)))
       #t
-      (and (not (any (lambda (x) (eq? (car a) x)) (cdr a)))
+      (and (not (any (lambda (x) (equal? (car a) x)) (cdr a)))
 	   (apply distinct? (cdr a)))))
 
 ;; Shamelessly ripped from https://wingolog.org/archives/2013/02/25/on-generators
@@ -96,6 +109,7 @@
 	value))))
 
 (define-syntax generator
+  ;; generator with an anaphoric yield
   (lambda (x)
     (syntax-case x ()
       [(generator expr ...)

test.scm

@@ -63,6 +63,13 @@
     (define value (upply -3 5 = abs 1-))
     (assert-equal #t value)))
 
+(define-test-suite "conjoin"
+  (define-test "test"
+    (assert-equal #t ((conjoin negative? odd? rational?) -3))
+    (assert-equal #f ((conjoin negative? odd? rational?) -4)))
+  (define-test "vacuous"
+    (assert-equal #t ((conjoin) '(some donkus)))))
+
 (define-test-suite "generator"
   (define-test "test"
     (define number-generator