From 917540309ba988799e33e071ed000b784012eccd Mon Sep 17 00:00:00 2001
From: Martin Henz <henz@comp.nus.edu.sg>
Date: Wed, 3 Jul 2024 07:32:55 +0800
Subject: [PATCH 1/9] fixes #764 (#1008)

---
 xml/chapter3/section3/subsection3.xml | 125 ++++++++++++++++++++++++++
 1 file changed, 125 insertions(+)

diff --git a/xml/chapter3/section3/subsection3.xml b/xml/chapter3/section3/subsection3.xml
index 1ac26c93a..992653629 100644
--- a/xml/chapter3/section3/subsection3.xml
+++ b/xml/chapter3/section3/subsection3.xml
@@ -686,6 +686,131 @@ const put = operation_table("insert");
     </SPLITINLINE>
     should take as input a list of keys used to access the table.
     <LABEL NAME="ex:3_25"/>
+    <SOLUTION>
+      <SNIPPET>
+	<NAME>solution_3_25</NAME>
+	<EXAMPLE>solution_3_25_example</EXAMPLE>
+	<JAVASCRIPT>
+// contributed by GitHub user tttinkl
+
+function assoc(key, records, same_key) {
+  return is_null(records)
+    ? undefined
+    : same_key(key, head(head(records)))
+    ? head(records)
+    : assoc(key, tail(records), same_key);
+}
+
+
+function make_table(same_key) {
+  const local_table = list("*table");
+
+  const get_value = tail;
+
+  function is_table(t) {
+    return is_pair(t) &amp;&amp; head(t) === "*table";
+  }
+
+  function lookup(keys) {
+    function lookup_generic(keys, table) {
+      if (is_null(keys)) {
+        return table;
+      }
+      const key_1 = head(keys);
+      const key_rest = tail(keys);
+      const record = assoc(key_1, tail(table), same_key);
+      if (is_undefined(record)) {
+        return undefined;
+      }
+      if (is_null(key_rest)) {
+        return get_value(record);
+      } else if (is_table(get_value(record))) {
+        return lookup_generic(key_rest, get_value(record));
+      } else {
+        error('invalid key');
+      }
+    }
+    return lookup_generic(keys, local_table);
+  }
+
+
+  function insert(keys, value) {
+    function insert_generic(keys, value, table) {
+      const key_1 = head(keys);
+      const key_rest = tail(keys);
+      const record = assoc(key_1, tail(table), same_key);
+      if (is_undefined(record)) {
+        if (is_null(key_rest)) {
+          set_tail(
+            table,
+            pair(pair(key_1, value), tail(table)));
+        } else {
+          const new_subtable = list("*table");
+          set_tail(
+            table,
+            pair(pair(key_1, new_subtable), tail(table))
+          );
+          insert_generic(key_rest, value, new_subtable);
+        }
+      } else {
+        if (is_null(key_rest)) {
+          set_tail(record, value);
+        } else {
+          if (is_table(get_value(record))) {
+            insert_generic(key_rest, value, get_value(record));
+          } else {
+            const new_subtable = list("*table");
+            set_tail(record, new_subtable);
+            insert_generic(key_rest, value, new_subtable);
+          }
+        }
+      }
+    }
+    insert_generic(keys, value, local_table);
+  }
+
+  function dispatch(m) {
+    return m === "lookup"
+      ? lookup
+      : m === "insert"
+      ? insert
+      : m === "show"
+      ? () => {
+        display(local_table);
+        return local_table;
+      }
+      : error(m, "unknow operation -- table");
+  }
+  return dispatch;
+}
+
+const table = make_table(equal);
+
+const get = table('lookup');
+const put = table('insert');
+const show = table('show');
+	</JAVASCRIPT>
+      </SNIPPET>
+      <SNIPPET HIDE="yes">
+	<NAME>solution_3_25_example</NAME>
+	<JAVASCRIPT>
+put(list("a"), 1);
+put(list("b", "c"), 2);
+put(list("d", "e", "f"), 3);
+
+display(get(list("a")));
+display(get(list("b", "c")));
+display(get(list("d", "e", "f")));
+
+put(list("a", "b"), 1);
+display(get(list("a")));
+put(list("b", "c", "d"), 2);
+display(get(list("b", "c")));
+put(list("b"), 1);
+display(get(list("b")));
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>

From 452c6b7106f5795714083a84d81d3bc439e7e544 Mon Sep 17 00:00:00 2001
From: Martin Henz <henz@comp.nus.edu.sg>
Date: Wed, 3 Jul 2024 07:36:36 +0800
Subject: [PATCH 2/9] fixes #796 (#1009)

---
 xml/chapter3/section1/subsection3.xml | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/xml/chapter3/section1/subsection3.xml b/xml/chapter3/section1/subsection3.xml
index d371b55e0..101b341e2 100644
--- a/xml/chapter3/section1/subsection3.xml
+++ b/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>

From 59a372506821057d524cef12d132502ba4515491 Mon Sep 17 00:00:00 2001
From: Martin Henz <henz@comp.nus.edu.sg>
Date: Wed, 3 Jul 2024 07:40:25 +0800
Subject: [PATCH 3/9] fixes #802 (#1010)

---
 xml/chapter3/section3/subsection1.xml | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/xml/chapter3/section3/subsection1.xml b/xml/chapter3/section3/subsection1.xml
index 4a219a588..3820d0a4e 100644
--- a/xml/chapter3/section3/subsection1.xml
+++ b/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));	

From 9d4ccbdc1fe00c14db16b25aec72730453a4cd53 Mon Sep 17 00:00:00 2001
From: Martin Henz <henz@comp.nus.edu.sg>
Date: Wed, 3 Jul 2024 08:11:30 +0800
Subject: [PATCH 4/9] fixes #804 (#1011)

* fixes #804

* credit
---
 xml/chapter3/section3/subsection2.xml | 98 +++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)

diff --git a/xml/chapter3/section3/subsection2.xml b/xml/chapter3/section3/subsection2.xml
index a1ce67fa5..f5dc416a9 100644
--- a/xml/chapter3/section3/subsection2.xml
+++ b/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>

From 245bdc06efa623432222e34eedc40b610e94d7eb Mon Sep 17 00:00:00 2001
From: Martin Henz <henz@comp.nus.edu.sg>
Date: Wed, 3 Jul 2024 08:19:06 +0800
Subject: [PATCH 5/9] fixes #805 (#1012)

---
 xml/chapter3/section3/subsection3.xml | 96 +++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)

diff --git a/xml/chapter3/section3/subsection3.xml b/xml/chapter3/section3/subsection3.xml
index 992653629..6536e7b86 100644
--- a/xml/chapter3/section3/subsection3.xml
+++ b/xml/chapter3/section3/subsection3.xml
@@ -826,6 +826,102 @@ display(get(list("b")));
     (e.g., numerically or alphabetically).  (Compare
     exercise<SPACE/><REF NAME="ex:set-lookup-binary-tree"/> of chapter<SPACE/><REF NAME="chap:data"></REF>.)
     <LABEL NAME="ex:3_26"/>
+    <SOLUTION>
+      <SNIPPET>
+	<NAME>ex_3_26_solution</NAME>
+	<EXAMPLE>ex_3_26_solution_example</EXAMPLE>
+	<JAVASCRIPT>
+// provided by GitHub user devinryu
+
+function entry(tree) { return head(tree); }
+function left_branch(tree) { return head(tail(tree)); }
+function right_branch(tree) { return head(tail(tail(tree))); }
+function make_tree(entry, left, right) { 
+    return list(entry, left, right);
+}
+
+// kv is list(key, value)
+function adjoin_set(kv, set) {
+    return is_null(set)
+           ? make_tree(kv, null, null)
+           : head(kv) === head(entry(set))
+           ? set
+           : head(kv) &lt; head(entry(set))
+           ? make_tree(entry(set),
+                       adjoin_set(kv, left_branch(set)),
+                       right_branch(set))
+           : make_tree(entry(set),
+                       left_branch(set),
+                       adjoin_set(kv, right_branch(set)));
+}
+
+function make_table() {
+    let local_table = null;
+    function lookup(given_key, tree_of_records) {
+        if (is_null(tree_of_records)) {
+            return null;
+        } else {
+            const this_entry = entry(tree_of_records);
+            const this_key = head(this_entry);
+            return given_key === this_key 
+                   ? this_entry
+                   : given_key &lt; this_key
+                   ? lookup(given_key, 
+                            left_branch(tree_of_records))
+                   : lookup(given_key, 
+                            right_branch(tree_of_records));
+        }
+    }
+    function insert(k, v) {
+        let record = lookup(k, local_table);
+        if(is_null(record)) {
+            local_table = adjoin_set(list(k, v), local_table);
+        } else {
+            // do nothing
+        }
+    }
+    function get(k) {
+        return head(tail(lookup(k, local_table)));
+    }
+    function print() {
+        return display(local_table);
+    }
+    function dispatch(m) {
+        return m === "lookup"
+        ? get
+        : m === "insert"
+        ? insert
+        : m  === "print"
+        ? print
+        : error(m, "error");
+    }
+    return dispatch;
+}
+	</JAVASCRIPT>
+      </SNIPPET>
+      <SNIPPET HIDE="yes">
+	<NAME>ex_3_26_solution_example</NAME>
+	<JAVASCRIPT>
+const t = make_table();
+const get = t("lookup");
+const put = t("insert");
+const print = t("print");
+
+// The test results
+
+put(3, "d");
+put(1, "a");
+put(2, "b");
+put(2, "c");
+put(4, "e");
+put(5, "f");
+
+print();
+
+display(get(2)); // displays: "b"
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>

From b3395b7c8093f406c0cedb7ea43d1f080a94051a Mon Sep 17 00:00:00 2001
From: Martin Henz <henz@comp.nus.edu.sg>
Date: Wed, 3 Jul 2024 08:25:24 +0800
Subject: [PATCH 6/9] fixes #807 (#1013)

* fixes #807

* no eval here
---
 xml/chapter2/section5/subsection3.xml | 31 +++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/xml/chapter2/section5/subsection3.xml b/xml/chapter2/section5/subsection3.xml
index 3971aca7e..8f76c839e 100644
--- a/xml/chapter2/section5/subsection3.xml
+++ b/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>

From 2d6eb30bfb519522bff434e0996d961f4fd9c689 Mon Sep 17 00:00:00 2001
From: Martin Henz <henz@comp.nus.edu.sg>
Date: Wed, 3 Jul 2024 08:29:56 +0800
Subject: [PATCH 7/9] fixes #810 (#1014)

---
 xml/chapter1/section1/subsection6.xml | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/xml/chapter1/section1/subsection6.xml b/xml/chapter1/section1/subsection6.xml
index b71815912..25accfdf2 100644
--- a/xml/chapter1/section1/subsection6.xml
+++ b/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>

From f352aa96862cfacf443231a3d66499442d06585d Mon Sep 17 00:00:00 2001
From: Martin Henz <henz@comp.nus.edu.sg>
Date: Wed, 3 Jul 2024 08:35:49 +0800
Subject: [PATCH 8/9] fixes #814 (#1015)

---
 xml/chapter4/section2/subsection1.xml | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/xml/chapter4/section2/subsection1.xml b/xml/chapter4/section2/subsection1.xml
index 4e287a53e..7243f0d75 100644
--- a/xml/chapter4/section2/subsection1.xml
+++ b/xml/chapter4/section2/subsection1.xml
@@ -342,6 +342,11 @@ factorial(5);
       <JAVASCRIPT>functions</JAVASCRIPT>
     </SPLITINLINE>
     work in a normal-order language?
+    <SOLUTION>
+      (provided by GitHub user joeng03)
+When evaluated in default (‘strict’) mode, the code undergoes applicative order reduction and runs into an infinite loop because it needs to evaluate the arguments of the unless function, but the factorial function does not have a terminating condition.
+When evaluated in lazy mode, the code undergoes normal order reduction. It produces the correct output because the unless function is applied before its arguments are evaluated.      
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>

From aef4e9cd5e455d9164b1cc3fb506268a9c64dc30 Mon Sep 17 00:00:00 2001
From: Martin Henz <henz@comp.nus.edu.sg>
Date: Wed, 3 Jul 2024 08:42:00 +0800
Subject: [PATCH 9/9] fixes #821 (#1016)

---
 xml/chapter2/section5/subsection1.xml | 49 ++++++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/xml/chapter2/section5/subsection1.xml b/xml/chapter2/section5/subsection1.xml
index bfd1a66d6..8f3e4192d 100644
--- a/xml/chapter2/section5/subsection1.xml
+++ b/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