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authorrsiddharth <s@ricketyspace.net>2019-07-06 23:00:06 -0400
committerrsiddharth <s@ricketyspace.net>2019-07-06 23:00:06 -0400
commita4a4996d7d9c6dcb7e48bafcfa5a91fe69d80f70 (patch)
tree583238493886be25ed6638842e5cd3fa1c96b66d /net/ricketyspace
parentcf005bd0c4b79167e2d97e6a51fc95fbb6fa820f (diff)
Add (net ricketyspace sicp two twentynine)
Ex 2.29 a, b. * net/ricketyspace/sicp/two/twentynine.scm: New file.
Diffstat (limited to 'net/ricketyspace')
-rw-r--r--net/ricketyspace/sicp/two/twentynine.scm61
1 files changed, 61 insertions, 0 deletions
diff --git a/net/ricketyspace/sicp/two/twentynine.scm b/net/ricketyspace/sicp/two/twentynine.scm
new file mode 100644
index 0000000..2340f38
--- /dev/null
+++ b/net/ricketyspace/sicp/two/twentynine.scm
@@ -0,0 +1,61 @@
+;;;; License: CC0-1.0
+
+(define-module (net ricketyspace sicp two twentynine)
+ #:export (make-mobile
+ make-branch
+ left-branch
+ right-branch
+ branch-length
+ branch-structure
+ total-weight))
+
+(define (make-mobile left right)
+ (list left right))
+
+(define (make-branch length structure)
+ (list length structure))
+
+(define (left-branch mobile)
+ (car mobile))
+
+(define (right-branch mobile)
+ (car (cdr mobile)))
+
+(define (branch-length branch)
+ (car branch))
+
+(define (branch-structure branch)
+ (car (cdr branch)))
+
+(define (total-weight mobile)
+ (define (branch-weight b)
+ (let ((bs (branch-structure b)))
+ (cond ((not (pair? bs)) bs)
+ (else (branch-weight bs)))))
+ (+ (branch-weight (left-branch mobile))
+ (branch-weight (right-branch mobile))))
+
+;;; Guile REPL
+;;;
+;;; scheme@(guile-user)> ,re (net ricketyspace sicp two twentynine)
+;;; scheme@(guile-user)> (make-mobile (make-branch 3 45) (make-branch 4 (make-branch 5 50)))
+;;; $4 = ((3 45) (4 (5 50)))
+;;; scheme@(guile-user)> (left-branch $4)
+;;; $5 = (3 45)
+;;; scheme@(guile-user)> (right-branch $4)
+;;; $6 = (4 (5 50))
+;;; scheme@(guile-user)> (branch-length (left-branch $4))
+;;; $7 = 3
+;;; scheme@(guile-user)> (branch-structure (left-branch $4))
+;;; $8 = 45
+;;; scheme@(guile-user)> (branch-length (right-branch $4))
+;;; $9 = 4
+;;; scheme@(guile-user)> (branch-structure (right-branch $4))
+;;; $10 = (5 50)
+;;; scheme@(guile-user)> (branch-length (branch-structure (right-branch $4)))
+;;; $11 = 5
+;;; scheme@(guile-user)> (branch-structure (branch-structure (right-branch $4)))
+;;; $12 = 50
+;;; scheme@(guile-user)> (total-weight $4)
+;;; $14 = 95
+