learning-sicp

commit 4a763364f95f99c0a6597d5f9a8049a741a5d048
parent d1f476d505795e81c81b09753a0eaba294a03e06
Author: Yuval Langer <yuval.langer@gmail.com>
Date:   Mon, 10 Apr 2023 14:35:21 +0300

Add solutions to exercise 1.30 and 1.31.

Diffstat:
A
sicp/solutions/1_30.scm
 | 
26
++++++++++++++++++++++++++
A
sicp/solutions/1_31.scm
 | 
51
+++++++++++++++++++++++++++++++++++++++++++++++++++
A
sicp/tests/1_30.scm
 | 
17
+++++++++++++++++
A
sicp/tests/1_31.scm
 | 
29
+++++++++++++++++++++++++++++

4 files changed, 123 insertions(+), 0 deletions(-)
diff --git a/sicp/solutions/1_30.scm b/sicp/solutions/1_30.scm
@@ -0,0 +1,26 @@
+(define-library (sicp solutions 1_30)
+  (import (scheme base))
+  (export
+   linear-recursive-sum
+   iterative-sum
+   )
+
+  (begin
+    (define (linear-recursive-sum term a next b)
+      (if (> a b)
+          0
+          (+ (term a)
+             (linear-recursive-sum term
+                                   (next a)
+                                   next
+                                   b))))
+
+    (define (iterative-sum term a next b)
+      (define (iter a result)
+        (if (> a b)
+            result
+            (iter (next a)
+                  (+ (term a)
+                     result)))
+        )
+      (iter a 0))))
diff --git a/sicp/solutions/1_31.scm b/sicp/solutions/1_31.scm
@@ -0,0 +1,51 @@
+(define-library (sicp solutions 1_31)
+  (import (scheme base))
+  (export
+   iterative-product
+   recursive-product
+   factorial
+   tau-approximation
+   )
+
+  (begin
+    (define (identity x) x)
+    (define (1+ x) (+ 1 x))
+    (define (1- x) (- 1 x))
+    
+    (define (iterative-product term a next b)
+      (define (iter a result)
+        (if (> a b)
+            result
+            (iter (next a)
+                  (* (term a)
+                     result))))
+      (iter a 1))
+
+    (define (factorial n)
+      (iterative-product identity
+                         1
+                         1+
+                         n))
+
+
+    (define (tau-approximation n)
+      (* 8
+         (iterative-product (lambda (x)
+                    (/  (if (odd? x)
+                            (+ 1 x)
+                            (+ 2 x))
+                        (if (odd? x)
+                            (+ 2 x)
+                            (+ 1 x))))
+                  1
+                  1+
+                  n)))
+
+    (define (recursive-product term a next b)
+      (if (> a b)
+          1
+          (* (term a)
+             (recursive-product term
+                                (next a)
+                                next
+                                b))))))
diff --git a/sicp/tests/1_30.scm b/sicp/tests/1_30.scm
@@ -0,0 +1,17 @@
+(define-library (sicp tests 1_30)
+  (import (scheme base))
+  (import (srfi :64))
+  (import (sicp solutions 1_30))
+
+  (begin
+    (test-begin "1.30")
+    (test-equal
+        (iterative-sum (lambda (x) (* x x))
+                       0
+                       (lambda (x) (+ 1 x))
+                       10)
+      (linear-recursive-sum (lambda (x) (* x x))
+                            0
+                            (lambda (x) (+ 1 x))
+                            10))
+    (test-end "1.30")))
diff --git a/sicp/tests/1_31.scm b/sicp/tests/1_31.scm
@@ -0,0 +1,29 @@
+(define-library (sicp tests 1_31)
+  (import (scheme base))
+  (import (srfi :1))
+  (import (srfi :64))
+  (import (sicp solutions 1_31))
+
+  (begin
+    (define fac-10
+      (reduce *
+              1
+              (iota 10 1)))
+
+    (test-begin "1.31")
+    (test-equal
+        fac-10
+      (factorial 10))
+    (test-equal
+        628
+      (floor (* 100 (tau-approximation 1000))))
+    (test-equal
+        (iterative-product (lambda (x) (* x x))
+                           1
+                           (lambda (x) (+ 2 x))
+                           10)
+      (recursive-product (lambda (x) (* x x))
+                         1
+                         (lambda (x) (+ 2 x))
+                         10))
+    (test-end "1.31")))