diff options
author | rsiddharth <s@ricketyspace.net> | 2020-04-05 16:29:46 -0400 |
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committer | rsiddharth <s@ricketyspace.net> | 2020-04-05 16:29:46 -0400 |
commit | be1b432a67d334b7f9fd19735827c1698b085970 (patch) | |
tree | e10317d964016b1b563f4e76fd8090ef3ef39a2d /net/ricketyspace/sicp/two/forty.scm | |
parent | 7f64b4262ee7c71c6fe2593cd00b5606a14a8155 (diff) |
Add (net ricketyspace sicp two forty).
Diffstat (limited to 'net/ricketyspace/sicp/two/forty.scm')
-rw-r--r-- | net/ricketyspace/sicp/two/forty.scm | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/net/ricketyspace/sicp/two/forty.scm b/net/ricketyspace/sicp/two/forty.scm new file mode 100644 index 0000000..e7c2851 --- /dev/null +++ b/net/ricketyspace/sicp/two/forty.scm @@ -0,0 +1,55 @@ +;;;; License: CC0-1.0 + +(define-module (net ricketyspace sicp two forty) + #:use-module (net ricketyspace sicp one twentyseven) + #:export (unique-pairs + prime-sum-pairs)) + + +(define (accumulate op initial sequence) + (if (null? sequence) + initial + (op (car sequence) + (accumulate op initial (cdr sequence))))) + + +(define (enumerate-interval low high) + (if (> low high) + '() + (cons low (enumerate-interval (+ low 1) high)))) + + +(define (prime-sum? pair) + (prime? (+ (car pair) (cadr pair)))) + + +(define (make-pair-sum pair) + (list (car pair) (cadr pair) (+ (car pair) (cadr pair)))) + + +(define (flatmap proc seq) + (accumulate append '() (map proc seq))) + + +(define (unique-pairs n) + (flatmap (lambda (i) + (map (lambda (j) (list i j)) + (enumerate-interval 1 (- i 1)))) + (enumerate-interval 1 n))) + + +(define (prime-sum-pairs n) + (map make-pair-sum + (filter prime-sum? + (unique-pairs n)))) + + +;;; +;;; Guile REPL +;;; +;;; scheme@(guile-user)> ,re (net ricketyspace sicp two forty) +;;; scheme@(guile-user)> (unique-pairs 6) +;;; $8 = ((2 1) (3 1) (3 2) (4 1) (4 2) (4 3) (5 1) (5 2) (5 3) (5 4) (6 1) (6 2) (6 3) (6 4) (6 5)) +;;; scheme@(guile-user)> (prime-sum-pairs 6) +;;; $9 = ((2 1 3) (3 2 5) (4 1 5) (4 3 7) (5 2 7) (6 1 7) (6 5 11)) +;;; |