Clean up

shared/util.scm

@@ -0,0 +1,132 @@
+(define (assert a b)
+  (cond ((equal? a b) (display "[ok]"))
+    (else
+      (display "[error] ")
+      (display a)
+      (display " != ")
+      (display b)))
+  (newline))
+
+; I have this here to avoid name-conflicts with the amb implementation in
+; amb.scm.
+(define (my-assert a b)
+  (cond ((equal? a b) (display "[ok]"))
+    (else
+      (display "[error] ")
+      (display a)
+      (display " != ")
+      (display b)))
+  (newline))
+
+(define (gcd a b)
+  (if (= b 0) (abs a) (gcd b (remainder a b))))
+
+(define (average a b) (/ (+ a b) 2.0))
+(define (id n) n)
+(define identity id)
+(define (inc n) (+ n 1))
+(define nil '())
+(define (divides? a b) (= (remainder b a) 0))
+(define (cube n) (* n n n))
+(define (even? n) (= (remainder n 2) 0))
+(define (odd? n) (= (remainder n 2) 1))
+
+; copied prime? from 1.21
+(define (find-divisor n test-divisor)
+  (cond ((> (square test-divisor) n) n)
+        ((divides? test-divisor n) test-divisor)
+        (else (find-divisor n (+ test-divisor 1)))))
+(define (smallest-divisor n)
+  (find-divisor n 2))
+(define (prime? n) (if (= n 1) #f (= n (smallest-divisor n))))
+
+; https://mitpress.mit.edu/sites/default/files/sicp/full-text/book/book-Z-H-15.html
+(define (enumerate-interval low high)
+  (if (> low high)
+      nil
+      (cons low (enumerate-interval (+ low 1) high))))
+
+; Returns #t if there is no #f in xs, otherwise returns #f.
+(define (all? xs)
+  (cond ((null? xs) #t)
+        ((eq? (car xs) #f) #f)
+        (else (all? (cdr xs)))))
+
+(define (all-eq? xs)
+  (cond ((null? xs) #t)
+        ((null? (cdr xs)) #t)
+        ((eq? (car xs) (cadr xs)) (all-eq? (cdr xs)))
+        (else #f)))
+
+(define (fold-right op initial sequence) ; same as accumulate
+  (if (null? sequence)
+      initial
+      (op (car sequence)
+          (fold-right op initial (cdr sequence)))))
+
+; From exercise 3.5
+(define (random-in-range low high)
+  (let ((range (- high low)))
+    (+ low (random range))))
+
+(define (contains x xs)
+  (cond
+    ((null? xs) #f)
+    ((eq? x (car xs)) #t)
+    (else (contains x (cdr xs)))))
+
+(define (display-line x)
+  (display x)
+  (newline))
+
+(define (take n xs)
+  (if (= n 0)
+    '()
+    (cons (stream-car xs)
+          (take (- n 1) (stream-cdr xs)))))
+
+(define (drop n xs)
+  (if (= n 0)
+    xs
+    (drop (- n 1) (stream-cdr xs))))
+
+(define (find item stream)
+  (define (iter n stream)
+    (if (equal? (stream-car stream) item)
+      n
+      (iter (+ n 1) (stream-cdr stream))))
+  (iter 0 stream))
+
+(define (display-stream s)
+  (stream-for-each display-line s))
+
+(define (show x)
+  (display-line x)
+  x)
+
+(define (stream-ref s n)
+  (if (= n 0)
+      (stream-car s)
+      (stream-ref (stream-cdr s) (- n 1))))
+
+(define (partial-sums xs)
+  (cons-stream (stream-car xs)
+               (add-streams (partial-sums xs)
+                            (stream-cdr xs))))
+
+(define (scale-stream stream factor)
+  (stream-map (lambda (x) (* x factor)) stream))
+
+(define (add-streams s1 s2)
+  (stream-map + s1 s2))
+
+(define (list->stream xs)
+  (if (null? xs)
+    '()
+    (cons-stream (car xs) (list->stream (cdr xs)))))
+
+(define ones (cons-stream 1 ones))
+
+(define integers (cons-stream 1 (add-streams ones integers)))
+
+'util-loaded