Paper problems + JS problems

paperproblems/HOF/problem1.txt

@@ -2,11 +2,28 @@ Someone has given you a function called filter
 You don't know what it does, but there are clues at the bottom of this file
 Use these clues to describe what filter is.
 Specifically:
- - How many parameters does it have
- - What are the types of the parameters
- - What does it do?
 
+****************************************< ANSWER >**********************************************
+
+ - How many parameters does it have?
+   * 2
+
+ - What are the types of the parameters?
+   * 1st argument is an array (...technically an 'object', but whatever. :D)
+   * 2nd argument is a function;
+
+ - What does it do?
+   1) First, we see that in all cases: it returns an array.
+   2) It iterates through each element in the array passed as the first argument, and 
+   3) checks, via the function passed as the second argument, whether the current element
+      evaluates to true or false in the conditional statements (if/else) executed within
+      the passed function...
+      a) If the expression evaluates to true: filter pushes the current element 
+         in the resulting array (presented in step 1);
+      b) If the expression evaluates to false: the element is not pushed to the resulting array.
+   4) The result, therefore, is an array of elements that passed the conditional tests as true.
 
+***************************************</ ANSWER >**********************************************
 
 var evenNumbers = [2, 4, 6, 8, 10];
 var oddNumbers = [3, 5, 7, 9];

paperproblems/HOF/problem2.txt

@@ -2,9 +2,27 @@ Someone has given you a function called map
 You don't know what it does, but there are clues at the bottom of this file
 Use these clues to describe what map is.
 Specifically:
- - How many parameters does it have
- - What are the types of the parameters
+
+****************************************< ANSWER >**********************************************
+
+ - How many parameters does it have?
+   * 2
+
+ - What are the types of the parameters?
+   * 1st argument is an array (...technically an 'object', but whatever. :D)
+   * 2nd argument is a function;
+
  - What does it do?
+   1) First, we see that in all cases: it returns an array.
+   2) It iterates through each element in the array passed as the first argument, and 
+   3) performs, via the function passed as the second argument, an operation on the 
+      current element, then pushes its result (the returned value) to the resulting 
+      array (presented in step 1).
+   4) The result, therefore, is an array of new elements that have been generated 
+      based on operations performed on the array's elements (within arg1) in the passed 
+      function (arg2).
+
+***************************************< /ANSWER >**********************************************
 
 var someNumbers = [1, 2, 3, 4];
 var someStrings = ["bob", "ERIC"];

paperproblems/HOF/problem3.txt

@@ -8,4 +8,19 @@ function f(g) {
     return g(3,5);
 }
 
-console.log(f(k));
+console.log(f(k));
+
+******************************************< ANSWER >********************************************
+
+This will return an error, because the 2 arguments of k are never actually specified anywhere
+(and certainly not by g...!)
+
+Specifically:
+k would *not* take the result of g as parameters to be passed down to itself; 
+rather, function f calls function k in an attempt to evaluate parameters it could pass into/as
+its argument g. However, function k is being called without any arguments -- and its arguments
+are necessary to evaluate the returned value.
+This program won't be able to add or multiply numbers to undefined arguments.
+I expect this will output either a type error or NaN (honestly, I'm not sure which).
+
+*****************************************</ ANSWER >********************************************

paperproblems/HOF/problem4.txt

@@ -12,4 +12,18 @@ function f(g, h) {
     return g(h, 1, 4);
 }
 
-console.log(f(k, m));
+console.log(f(k, m));
+
+******************************************< ANSWER >********************************************
+
+This will return an error, because the 3 arguments of k and the argument of m are never actually specified anywhere.
+
+Specifically:
+f would *not* take the result of k as parameters to be passed down to itself; 
+rather, function f calls function k in an attempt to evaluate parameters it could pass into/as its argument g. However, function k is being called without any arguments -- and its arguments are necessary to evaluate the returned value.
+Moreover, nothing is passed as an argument for m (as x). Double whammy.
+
+This program won't be able to add or multiply numbers to undefined arguments.
+I expect this will output either a type error or NaN (honestly, I'm not sure which).
+
+*****************************************</ ANSWER >********************************************

paperproblems/__proto__/problem1.txt

@@ -1,10 +1,31 @@
-Draw the object diagram for this program
+Draw the object diagram for this program
 
 var x1 = {};
 var x2 = {};
 var x3 = {};
 var x4 = {};
-x2.__proto__ = x1;
-x3.__proto__ = x2;
-x4.__proto__ = x3;
+x2.__proto__ = x1; // Impossible, would result in type error (cannot overwrite proto as a whole)
+x3.__proto__ = x2; // Impossible, would result in type error (cannot overwrite proto as a whole)
+x4.__proto__ = x3; // Impossible, would result in type error (cannot overwrite proto as a whole)
 
+****************************************< ANSWER >**********************************************
+
+   ╔════╤═══╗
+   ║    │   ║ ┌────┬───┐
+   ║ x1 │ ■───┤ {} │ ■────┐
+   ║    │   ║ └────┴───┘  │
+   ╟────┼───╢             │
+   ║    │   ║ ┌────┬───┐  │
+   ║ x2 │ ■───┤ {} │ ■────┤
+   ║    │   ║ └────┴───┘  │  ┌───────────┬─────┐
+   ╟────┼───╢             ├─►│ __proto__ │ ... │
+   ║    │   ║ ┌────┬───┐  │  └───────────┴─────┘
+   ║ x3 │ ■───┤ {} │ ■────┤
+   ║    │   ║ └────┴───┘  │
+   ╟────┼───╢             │
+   ║    │   ║ ┌────┬───┐  │
+   ║ x4 │ ■───┤ {} │ ■────┘
+   ║    │   ║ └────┴───┘
+   ╚════╧═══╝
+
+***************************************</ ANSWER >**********************************************

paperproblems/__proto__/problem2.txt

@@ -4,14 +4,28 @@ var x1 = {};
 var x2 = {};
 var x3 = {};
 var x4 = {};
-x2.__proto__ = x1;
-x3.__proto__ = x2;
-x4.__proto__ = x3;
+x2.__proto__ = x1; // Impossible, would result in type error (cannot overwrite proto as a whole)
+x3.__proto__ = x2; // Impossible, would result in type error (cannot overwrite proto as a whole)
+x4.__proto__ = x3; // Impossible, would result in type error (cannot overwrite proto as a whole)
+
+// Therefore...
 
 x1.age = 20;
 x3.age = 18;
 
 console.log(x1.age);
 console.log(x2.age);
 console.log(x3.age);
-console.log(x4.age);
+console.log(x4.age);
+
+*************************************************< ANSWER >***************************************************
+
+Technically, if you didn't remove the last three lines modifying __proto__ : you would get a type error.
+...Once that was cleaned up; this is what we'd get:
+
+1st console.log:    20
+2nd console.log:    18 // None defined in object; last assigned key-value pair 'age' for __proto__ takes over.
+3rd console.log:    18
+4th console.log:    18 // None defined in object; last assigned key-value pair 'age' for __proto__ takes over.
+
+*************************************************</ ANSWER >**************************************************

paperproblems/__proto__/problem3.txt

@@ -11,4 +11,12 @@ You get the following exception:
 
 
 a) Explain what this exception means.
-b) Why does this exception exist? What's wrong with a cyclic __proto__ value?
+   * A __proto__ object would be generated and destroyed (overriden by an empty object, 
+     which itself points to a __proto__ object...) over and over again, indefintely.
+     It is an endless loop and therefore cyclic.
+     Ergo: a creepy, ouroboric, self-cannibalistic mess that must be avoided at all costs. :)
+
+b) Why does this exception exist? What's wrong with a cyclic __proto__ value?
+   * This happens because we're trying to override the entirety of the __proto__ object, 
+     which is a feature (implicit object) required to allow for Object-Oriented Programming in JavaScript.
+     An override would result in an infinite loop; because objects point to the __proto__ object when instantiated...

paperproblems/anonymous-functions/problem1.txt

@@ -1,8 +1,15 @@
-Rewrite this program so that it doesn't have a single function definition
-In other words, replace all the function definitions with anonymous functions
-
-function greet(x) {
-    console.log("hello " + x);
-}
-
-greet(bob);
+Rewrite this program so that it doesn't have a single function definition
+In other words, replace all the function definitions with anonymous functions
+
+****************<ANSWER>******************
+
+const x = "Bob";
+
+function greet() {
+    console.log("hello " + x);
+}
+
+greet();
+
+****************</ANSWER>*****************
+

paperproblems/anonymous-functions/problem2.txt

@@ -1,14 +1,5 @@
-Rewrite this program so that it doesn't have a single function definition
-In other words, replace all the function definitions with anonymous functions
-The final program should be on a single line
-
-
-function greet(x) {
-    console.log("hello " + x);
-}
-
-function call(f) {
-    f("bob");
-}
-
-call(greet);
+Rewrite this program so that it doesn't have a single function definition
+In other words, replace all the function definitions with anonymous functions
+The final program should be on a single line
+
+const f = "bob", greet = () => console.log("hello " + f);

paperproblems/anonymous-functions/problem3.txt

@@ -1,12 +1,9 @@
-Rewrite this program so that it doesn't have a single function definition
-In other words, replace all the function definitions with anonymous functions
-
-function greet(x, y) {
-    console.log("hello " + x + " " + y);
-}
-
-function call(f) {
-    f("Bob", "Dole");
-}
-
-call(greet);
+Rewrite this program so that it doesn't have a single function definition
+In other words, replace all the function definitions with anonymous functions
+
+const x = "Bob";
+const y = "Dole";
+
+function greet() {console.log("hello " + x + " " + y)}
+
+greet();

paperproblems/anonymous-functions/problem4.txt

@@ -1,13 +1,4 @@
-Rewrite this program so that it doesn't have a single function definition
-In other words, replace all the function definitions with anonymous functions
-
-function greet(x) {
-    console.log("hello " + x);
-}
-
-function twice(f) {
-    f("bob");
-    f("mary");
-}
-
-twice(greet);
+Rewrite this program so that it doesn't have a single function definition
+In other words, replace all the function definitions with anonymous functions
+
+const f = "bob", greet = () => console.log("hello " + f);

paperproblems/anonymous-functions/problem5.txt

@@ -1,19 +1,25 @@
-What is the output of this program? Don't cheat by running it!
-
-function askOnADate(n) {
-    if(n === "Bob") return "I do!";
-    else return "Absolutely not!";
-}
-
-function soften(f) {
-    return function(name) {
-        var r = f(name);
-        if(r !== "I do!") return "maybe";
-        else return r;
-    }
-    return ret;
-}
-
-var softAskOnADate = soften(askOnADate);
-console.log(softAskOnADate("Eric"));
-console.log(softAskOnADate("Bob"));
+What is the output of this program? Don't cheat by running it!
+
+**********************************<ANSWER>***********************************
+"maybe" --- Softening applied for Eric (r !== "I do!")
+"I do!" --- No softening is applied for Bob (r === "I do!")
+ret is never actually used anywhere and could be removed altogether.
+**********************************</ANSWER>**********************************
+
+function askOnADate(n) {
+    if(n === "Bob") return "I do!";
+    else return "Absolutely not!";
+}
+
+function soften(f) {
+    return function(name) {
+        var r = f(name);
+        if(r !== "I do!") return "maybe";
+        else return r;
+    }
+    return ret;
+}
+
+var softAskOnADate = soften(askOnADate);
+console.log(softAskOnADate("Eric"));
+console.log(softAskOnADate("Bob"));

paperproblems/array-functions/problem1.txt

@@ -1,16 +1,33 @@
-What is the output of this program?
-
-var animals = [
-    {species: 'dog', name: 'Nacho'},
-    {species: 'cat', name: 'Ramses'},
-    {species: 'bunny',name: 'Flufftail'},
-    {species: 'dog', name: 'Popcorn'},
-    {species: 'giraffe', name: 'Neckbeard'},
-    {species: 'possum', name: ''}
-];
-
-var dogs = animals.filter(
-                function(animal)
-                     {return animal.species === 'dog';});
-
+What is the output of this program?
+
+***************************<ANSWER>***************************
+
+It will return 2.
+
+The animal array's filter function will look for animals
+whoses value of species corresponds to the value of 'dog';
+since filter returns only items where the evaluation 
+expression returns true.
+
+The filter function *does* return a new array; so it *can*
+be assigned to variable 'dogs'.
+
+dogs will contain an array containing 2 objects with 'dog' as
+value of key 'species'.
+
+***************************</ANSWER>**************************
+
+var animals = [
+    {species: 'dog', name: 'Nacho'},
+    {species: 'cat', name: 'Ramses'},
+    {species: 'bunny',name: 'Flufftail'},
+    {species: 'dog', name: 'Popcorn'},
+    {species: 'giraffe', name: 'Neckbeard'},
+    {species: 'possum', name: ''}
+];
+
+var dogs = animals.filter(
+                function(animal)
+                     {return animal.species === 'dog';});
+
 console.log(dogs.length);