Merge branch 'master' into 3-3-3-bug

xml/chapter1/section1/subsection6.xml

@@ -965,6 +965,24 @@ a === 4
       </JAVASCRIPT>
     </SPLIT>
     <LABEL NAME="ex:1_1"/>
+    <SOLUTION>
+      Solution provided by GitHub user Emekk
+      <OL>
+	<LI>10</LI>
+	<LI>12</LI>
+	<LI>8</LI>
+	<LI>3</LI>
+	<LI>6</LI>
+	<LI>3</LI>
+	<LI>4</LI>
+	<LI>19</LI>
+	<LI>false</LI>
+	<LI>4</LI>
+	<LI>16</LI>
+	<LI>6</LI>
+	<LI>16</LI>
+      </OL>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>

xml/chapter2/section5/subsection1.xml

@@ -932,7 +932,54 @@ function contents(datum) {
     arithmetic package.  This operation should work for ordinary numbers,
     rational numbers, and complex numbers.
     <LABEL NAME="ex:equ?"/>
-  </EXERCISE>
+    <SOLUTION>
+      <SNIPPET EVAL="no">
+	<JAVASCRIPT>
+// provided by GitHub user clean99
+
+function is_equal(x, y) {
+    return apply_generic("is_equal", list(x, y));
+}
+
+function install_javascript_number_package() {
+    // ...
+
+    put("is_equal", list("javascript_number", "javascript_number"),
+           (x, y) => x === y);
+
+    // ...
+}
+
+function install_rational_package() {
+    // ...
+
+    function is_equal(x, y) {
+        return numer(x) * denom(y) === numer(y) * denom(x);
+    }
+
+    put("is_equal", list("rational", "rational"), is_equal);
+
+    // ...
+}
+
+function install_complex_package() {
+    // ...
+
+    function is_equal(z1, z2) {
+        return real_part(z1) === real_part(z2)
+               ? imag_part(z1) === imag_part(z2)
+               : false;
+    }
+
+    put("is_equal", list("complex", "complex"),
+            is_equal);
+
+    //...
+}
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
+</EXERCISE>
 
   <EXERCISE>
     Define a generic predicate

xml/chapter2/section5/subsection3.xml

@@ -1025,6 +1025,37 @@ head(tail(tail(tail(mul(p1, p2)))));
     subtraction of polynomials.
     (Hint: You may find it helpful to define a generic negation operation.)
     <LABEL NAME="ex:sub-poly"/>
+    <SOLUTION>
+      <SNIPPET EVAL="no">
+	<NAME>ex_2_88_solution</NAME>
+	<JAVASCRIPT>
+function sub_terms(L1, L2) {
+    if (is_empty_termlist(L1)) {
+        return L2;
+    } else if (is_empty_termlist(L2)) {
+        return L1;
+    } else {
+        const t1 = first_term(L1);
+        const t2 = first_term(L2);
+        return order(t1) &gt; order(t2)
+               ? adjoin_term(t1, sub_terms(rest_terms(L1), L2))
+               : order(t1) &lt; order(t2)
+               ? adjoin_term(t2, sub_terms(L1, rest_terms(L2)))
+               : adjoin_term(make_term(order(t1), 
+                                       sub(coeff(t1), coeff(t2))),
+                             sub_terms(rest_terms(L1),
+                                       rest_terms(L2)));
+    }
+}
+function sub_poly(p1, p2) {
+    return is_same_variable(variable(p1), variable(p2))
+           ? make_poly(variable(p1),
+                       sub_terms(term_list(p1), term_list(p2)))
+           : error(list(p1, p2), "polys not in same var -- sub_poly");
+}
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>

xml/chapter3/section1/subsection3.xml

@@ -1091,22 +1091,20 @@ paul_acc("withdraw", "rosebud")(50); // Withdraws 50, should return 40
       <SNIPPET>
         <EXAMPLE>exercise_3_8_solution_example</EXAMPLE>
       <JAVASCRIPT>
-function make_f(init) {
-    return x => {
-        init = x - init;
-        return init;
-    };
+let v = -0.5;
+function f(x) {
+    v = x + v;
+    return v;
 }
-
-const f = make_f(1/2);
       </JAVASCRIPT>
       </SNIPPET>
 
       <SNIPPET HIDE="yes">
         <NAME>exercise_3_8_solution_example</NAME>
       <JAVASCRIPT>
-display(f(1) + f(0));
-display(f(0) + f(1));
+// try these separately
+display(f(0) + f(1)); // returns 0
+display(f(1) + f(0)); // returns 1
       </JAVASCRIPT>
       </SNIPPET>
     </SOLUTION>

xml/chapter3/section3/subsection1.xml

@@ -1441,6 +1441,7 @@ set_to_wow(z2);
       <JAVASCRIPT>function</JAVASCRIPT>
     </SPLITINLINE>
     <SNIPPET EVAL="yes">
+      <NAME>count_pairs</NAME>
       <INDEX><DECLARATION>count_pairs</DECLARATION><FRAGILE/></INDEX> 
       <SCHEME>
 (define (count-pairs x)
@@ -1476,18 +1477,18 @@ function count_pairs(x) {
     <SOLUTION>
       <SNIPPET>
         <NAME>exercise_3_16_solution</NAME>
+	<REQUIRES>count_pairs</REQUIRES>
         <EXAMPLE>exercise_3_16_solution_example</EXAMPLE>
         <SCHEME>
         </SCHEME>
         <JAVASCRIPT>
-const cycle = make_cycle(three_list);
-
 const three_list = list("a", "b", "c");
-
-const one = pair("a", "b");
-const three = pair(one, one);
-const four = pair(three, "c");
-const seven = pair(three, three);
+const one = pair("d", "e");
+const two = pair(one, one);
+const four_list = pair(two, "f");
+const seven_list = pair(two, two);
+const cycle = list("g", "h", "i");
+set_tail(tail(tail(cycle)), cycle);
         </JAVASCRIPT>
       </SNIPPET>
 
@@ -1496,8 +1497,8 @@ const seven = pair(three, three);
 	      <JAVASCRIPT>
 // return 3; return 4; return 7;
 display(count_pairs(three_list));
-display(count_pairs(four));
-display(count_pairs(seven));
+display(count_pairs(four_list));
+display(count_pairs(seven_list));
 
 // never return at all
 display(count_pairs(cycle));	

xml/chapter3/section3/subsection2.xml

@@ -738,6 +738,34 @@ delete_queue(q1);
     </SPLITINLINE>
     that takes a queue as input and prints the sequence of items in the queue.
     <LABEL NAME="ex:3_21"/>
+    <SOLUTION>
+      <SNIPPET>
+	<REQUIRES>make_queue</REQUIRES>
+	<REQUIRES>modify_pointers</REQUIRES>
+	<REQUIRES>insert_queue</REQUIRES>
+	<REQUIRES>is_empty_queue</REQUIRES>
+	<REQUIRES>delete_queue</REQUIRES>
+	<EXAMPLE>ex_3_21_solution_example</EXAMPLE>
+	<JAVASCRIPT>
+function print_queue(q) {
+    return display(head(q));
+}
+	</JAVASCRIPT>
+      </SNIPPET>
+      <SNIPPET HIDE="yes">
+	<NAME>ex_3_21_solution_example</NAME>
+	<JAVASCRIPT>
+const q1 = make_queue();
+print_queue(q1); // prints: null
+insert_queue(q1, "a");
+print_queue(q1); // prints: ["a", null]
+insert_queue(q1, "b");
+print_queue(q1); // prints: ["a", ["b", null]]
+delete_queue(q1);
+print_queue(q1); // prints: ["b", null]
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>
@@ -786,6 +814,76 @@ function make_queue() {
     and provide implementations of the queue operations using this
     representation.
     <LABEL NAME="ex:3_22"/>
+    <SOLUTION>
+      <SNIPPET>
+	<EXAMPLE>ex_3_22_example</EXAMPLE>
+	<JAVASCRIPT>
+// provided by GitHub user devinryu	  
+
+function make_queue() {
+    let front_ptr = null;
+    let rear_ptr = null;
+    function is_empty_queue() {
+        return is_null(front_ptr);
+    }
+    function insert_queue(item) {
+        let new_pair = pair(item, null);
+        if (is_empty_queue()) {
+            front_ptr = new_pair;
+            rear_ptr = new_pair;
+        } else {
+            set_tail(rear_ptr, new_pair);
+            rear_ptr = new_pair;
+        }
+    }
+    function delete_queue() {
+        if (is_empty_queue()) {
+            error("FRONT called with an empty queue");
+        } else {
+            front_ptr = tail(front_ptr);
+        }
+    }
+    function print_queue() {
+        display(front_ptr);
+    }
+    function dispatch(m) {
+        return m === "insert_queue"
+        ? insert_queue
+        : m === "delete_queue"
+        ? delete_queue
+        : m === "is_empty_queue"
+        ? is_empty_queue
+        : m === "print_queue"
+        ? print_queue
+        : error(m, "Unknow operation -- DISPATCH");
+    }
+    return dispatch;
+}
+function insert_queue(queue, item) {
+    return queue("insert_queue")(item);
+}
+function delete_queue(queue) {
+    return queue("delete_queue")();
+}
+function print_queue(queue) {
+    return queue("print_queue")();
+}
+	</JAVASCRIPT>
+      </SNIPPET>
+      <SNIPPET HIDE="yes">
+	<NAME>ex_3_22_example</NAME>
+	<JAVASCRIPT>
+const q = make_queue();
+print_queue(q); // prints: null
+insert_queue(q, "a");
+print_queue(q); // prints: ["a", null]
+insert_queue(q, "b");
+print_queue(q); // prints: ["a", ["b", null]]
+delete_queue(q);
+print_queue(q); // prints: ["b", null]
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>