Exercise 2.75 (#152)

Exercise 2.75 from Chapter 2 part 4 about implementing `make-from-mag-ang` in message-passing style has been added. This solution is meant to be analogous to the `make-from-real-imag` provided in the book.

README.md

@@ -1,7 +1,7 @@
 # Solving exercises from SICP with Clojure
 
 [![Clojure CI](https://github.com/SmetDenis/Clojure-Sicp/actions/workflows/main.yml/badge.svg?branch=main)](https://github.com/SmetDenis/Clojure-Sicp/actions/workflows/main.yml)
-![Progress](https://progress-bar.dev/120/?scale=356&title=Solved&width=500&suffix=)
+![Progress](https://progress-bar.dev/121/?scale=356&title=Solved&width=500&suffix=)
 
 SICP (Structure and Interpretation of Computer Programs) is the book of Harold Abelson and Gerald
 Jay Sussman on basics of computer science and software engineering.
@@ -42,7 +42,7 @@ Jay Sussman on basics of computer science and software engineering.
 
 ### Chapter 2 - Building Abstractions with Data
 
-![Progress](https://progress-bar.dev/74/?scale=97&title=Solved&width=500&suffix=)
+![Progress](https://progress-bar.dev/75/?scale=97&title=Solved&width=500&suffix=)
 
 * [2.1](https://sarabander.github.io/sicp/html/Chapter-2.xhtml#Chapter-2) Introduction to Data Abstraction - [Code in book](src/sicp/chapter_2/part_1/book_2_1.clj)
   * [2.1.1](https://sarabander.github.io/sicp/html/2_002e1.xhtml#g_t2_002e1_002e1) Example: Arithmetic Operations for Rational Numbers - [2.1](src/sicp/chapter_2/part_1/ex_2_01.clj)
@@ -62,7 +62,7 @@ Jay Sussman on basics of computer science and software engineering.
 * [2.4](https://sarabander.github.io/sicp/html/2_002e4.xhtml#g_t2_002e4) Multiple Representations for Abstract Data
   * [2.4.1](https://sarabander.github.io/sicp/html/2_002e4.xhtml#g_t2_002e4_002e1) Representations for Complex Numbers
   * [2.4.2](https://sarabander.github.io/sicp/html/2_002e4.xhtml#g_t2_002e4_002e2) Tagged data
-  * [2.4.3](https://sarabander.github.io/sicp/html/2_002e4.xhtml#g_t2_002e4_002e3) Data-Directed Programming and Additivity - [2.73](src/sicp/chapter_2/part_4/ex_2_73.clj), [2.74](src/sicp/chapter_2/part_4/ex_2_74.clj)
+  * [2.4.3](https://sarabander.github.io/sicp/html/2_002e4.xhtml#g_t2_002e4_002e3) Data-Directed Programming and Additivity - [2.73](src/sicp/chapter_2/part_4/ex_2_73.clj), [2.74](src/sicp/chapter_2/part_4/ex_2_74.clj), [2.75](src/sicp/chapter_2/part_4/ex_2_75.clj)
 * 2.5 Systems with Generic Operations
   * 2.5.1 Generic Arithmetic Operations
   * 2.5.2 Combining Data of Different Types

src/sicp/chapter_2/part_4/book_2_4.clj

@@ -134,15 +134,15 @@
     (polar? z) (angle-polar (contents z))
     :else (throw (Exception. (str "Unknown type: ANGLE " z)))))
 
-(defn make-from-real-imag [x y]
+(defn make-from-real-imag-v2 [x y]
   (make-from-real-imag-rectangular x y))
 
 (defn add-complex [z1 z2]
-  (make-from-real-imag
+  (make-from-real-imag-v2
     (+ (real-part z1) (real-part z2))
     (+ (imag-part z1) (imag-part z2))))
 
-(defn make-from-mag-ang [r a]
+(defn make-from-mag-ang-v2 [r a]
   (make-from-mag-ang-polar r a))
 
 (comment "2.4.3")
@@ -160,3 +160,15 @@
       (apply proc (map contents args))
       (throw (Exception. (str "No method for these types: APPLY-GENERIC "
                               (list op type-tags)))))))
+
+(defn make-from-real-imag [x y]
+  (fn [op]
+    (cond
+      (= op :real-part) x
+      (= op :imag-part) y
+      (= op :magnitude) (Math/sqrt (+ (* x x) (* y y)))
+      (= op :angle) (Math/atan2 y x)
+      :else (throw (Exception. (str "Unknown op: MAKE-FROM-REAL-IMAG " op))))))
+
+(defn apply-generic-v2 [op arg] (arg op))
+

src/sicp/chapter_2/part_4/ex_2_75.clj

@@ -0,0 +1,15 @@
+(ns sicp.chapter-2.part-4.ex-2-75)
+
+; Exercise 2.75
+;
+; Implement the constructor make-from-mag-ang in message-passing style.
+; This procedure should be analogous to the make-from-real-imag procedure given above.
+
+(defn make-from-mag-ang [r a]
+  (fn [op]
+    (cond
+      (= op :real-part) (* r (Math/cos a))
+      (= op :imag-part) (* r (Math/sin a))
+      (= op :magnitude) r
+      (= op :angle) a
+      :else (throw (Exception. (str "Unknown op: MAKE-FROM-REAL-IMAG " op))))))