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-rw-r--r--net/ricketyspace/sicp/two/thirtyone.scm22
1 files changed, 22 insertions, 0 deletions
diff --git a/net/ricketyspace/sicp/two/thirtyone.scm b/net/ricketyspace/sicp/two/thirtyone.scm
new file mode 100644
index 0000000..6420e25
--- /dev/null
+++ b/net/ricketyspace/sicp/two/thirtyone.scm
@@ -0,0 +1,22 @@
+;;;; License: CC0-1.0
+
+(define-module (net ricketyspace sicp two thirtyone)
+ #:export (tree-map
+ square-tree))
+
+(define (tree-map fun tree)
+ (cond ((null? tree) '())
+ ((not (pair? tree)) (fun tree))
+ (else (cons (tree-map fun (car tree))
+ (tree-map fun (cdr tree))))))
+
+(define (square-tree tree) (tree-map (lambda (x) (* x x)) tree))
+
+;;; Guile REPL
+;;;
+;;; scheme@(guile-user)> ,user (net ricketyspace sicp two thirtyone)
+;;; scheme@(guile-user)> (square-tree
+;;; (list 1
+;;; (list 2 (list 3 4) 5)
+;;; (list 6 7)))
+;;; $2 = (1 (4 (9 16) 25) (36 49))