Merge remote-tracking branch 'upstream/master'

c.html.markdown

@@ -0,0 +1,338 @@
+---
+language: c
+author: Adam Bard
+author_url: http://adambard.com/
+---
+
+Ah, C. Still the language of modern high-performance computing.
+
+C is the lowest-level language most programmers will ever use, but
+it more than makes up for it with raw speed. Just be aware of its manual
+memory management and C will take you as far as you need to go.
+
+```c
+// Single-line comments start with //
+/*
+Multi-line comments look like this.
+*/
+
+// Import headers with #include
+#include <stdlib.h>
+#include <stdio.h>
+
+// Declare function signatures in advance in a .h file, or at the top of
+// your .c file.
+void function_1();
+void function_2();
+
+// Your program's entry point is a function called
+// main with an integer return type.
+int main(){
+
+// print output using printf, for "print formatted"
+// %d is an integer, \n is a newline
+printf("%d\n", 0); // => Prints 0
+// All statements must end with a semicolon
+
+///////////////////////////////////////
+// Types
+///////////////////////////////////////
+
+// Variables must always be declared with a type.
+
+// 32-bit integer
+int x_int = 0;
+
+// 16-bit integer
+short x_short = 0;
+
+// 8-bit integer, aka 1 byte
+char x_char = 0;
+char y_char = 'y'; // Char literals are quoted with ''
+
+long x_long = 0; // Still 32 bytes for historical reasons
+long long x_long_long = 0; // Guaranteed to be at least 64 bytes
+
+// 32-bit floating-point decimal
+float x_float = 0.0;
+
+// 64-bit floating-point decimal
+double x_double = 0.0;
+
+// Integer types may be unsigned
+unsigned char ux_char;
+unsigned short ux_short;
+unsigned int ux_int;
+unsigned long long ux_long_long;
+
+// Arrays must be initialized with a concrete size.
+char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes
+int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes
+
+
+// You can initialize an array to 0 thusly:
+char my_array[20] = {0};
+
+// Indexing an array is like other languages -- or,
+// rather, other languages are like C
+my_array[0]; // => 0
+
+// Arrays are mutable; it's just memory!
+my_array[1] = 2;
+printf("%d\n", my_array[1]); // => 2
+
+// Strings are just lists of chars terminated by a null (0x00) byte.
+char a_string[20] = "This is a string";
+
+/*
+You may have noticed that a_string is only 16 chars long.
+Char #17 is a null byte, 0x00 aka \0. 
+Chars #18, 19 and 20 have undefined values.
+*/
+
+printf("%d\n", a_string[16]);
+
+///////////////////////////////////////
+// Operators
+///////////////////////////////////////
+
+int i1 = 1, i2 = 2; // Shorthand for multiple declaration
+float f1 = 1.0, f2 = 2.0;
+
+// Arithmetic is straightforward
+i1 + i2; // => 3
+i2 - i1; // => 1
+i2 * i1; // => 2
+i1 / i2; // => 0 (0.5, but truncated towards 0)
+
+f1 / f2; // => 0.5, plus or minus epsilon
+
+// Modulo is there as well
+11 % 3; // => 2
+
+// Comparison operators are probably familiar, but
+// there is no boolean type in c. We use ints instead.
+// 0 is false, anything else is true
+3 == 2; // => 0 (false)
+3 != 2; // => 1 (true)
+3 > 2; // => 1
+3 < 2; // => 0
+2 <= 2; // => 1
+2 >= 2; // => 1
+
+// Logic works on ints
+!3; // => 0 (Logical not)
+!0; // => 1
+1 && 1; // => 1 (Logical and)
+0 && 1; // => 0
+0 || 1; // => 1 (Logical or)
+0 || 0; // => 0
+
+// Bitwise operators!
+~0x0F; // => 0xF0 (bitwise negation)
+0x0F & 0xF0; // => 0x00 (bitwise AND)
+0x0F | 0xF0; // => 0xFF (bitwise OR)
+0x04 ^ 0x0F; // => 0x0B (bitwise XOR)
+0x01 << 1; // => 0x02 (bitwise left shift (by 1))
+0x02 >> 1; // => 0x01 (bitwise right shift (by 1))
+
+///////////////////////////////////////
+// Control Structures
+///////////////////////////////////////
+
+if(0){
+  printf("I am never run\n");
+}else if(0){
+  printf("I am also never run\n");
+}else{
+  printf("I print\n");
+}
+
+// While loops exist
+int ii = 0;
+while(ii < 10){
+    printf("%d, ", ii++); // ii++ increments ii in-place, after using its value.
+} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
+
+printf("\n");
+
+int kk = 0;
+do{
+    printf("%d, ", kk);
+}while(++kk < 10); // ++kk increments kk in-place, before using its value
+// => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
+
+printf("\n");
+
+// For loops too
+int jj;
+for(jj=0; jj < 10; jj++){
+    printf("%d, ", jj);
+} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
+
+printf("\n");
+
+///////////////////////////////////////
+// Typecasting
+///////////////////////////////////////
+
+// Everything in C is stored somewhere in memory. You can change
+// the type of a variable to choose how to read its data
+
+int x_hex = 0x01; // You can assign vars with hex literals
+
+// Casting between types will attempt to preserve their numeric values
+printf("%d\n", x_hex); // => Prints 1
+printf("%d\n", (short) x_hex); // => Prints 1
+printf("%d\n", (char) x_hex); // => Prints 1
+
+// Types will overflow without warning
+printf("%d\n", (char) 257); // => 1 (Max char = 255)
+printf("%d\n", (short) 65537); // => 1 (Max short = 65535)
+
+///////////////////////////////////////
+// Pointers
+///////////////////////////////////////
+
+// You can retrieve the memory address of your variables,
+// then mess with them.
+
+int x = 0;
+printf("%p\n", &x); // Use & to retrieve the address of a variable
+// (%p formats a pointer)
+// => Prints some address in memory;
+
+int x_array[20]; // Arrays are a good way to allocate a contiguous block of memory
+int xx;
+for(xx=0; xx<20; xx++){
+    x_array[xx] = 20 - xx;
+} // Initialize x_array to 20, 19, 18,... 2, 1
+
+// Pointer types end with *
+int* x_ptr = x_array;
+// This works because arrays are pointers to their first element.
+
+// Put a * in front to de-reference a pointer and retrieve the value,
+// of the same type as the pointer, that the pointer is pointing at.
+printf("%d\n", *(x_ptr)); // => Prints 20
+printf("%d\n", x_array[0]); // => Prints 20
+
+// Pointers are incremented and decremented based on their type
+printf("%d\n", *(x_ptr + 1)); // => Prints 19
+printf("%d\n", x_array[1]); // => Prints 19
+
+// Array indexes are such a thin wrapper around pointer
+// arithmetic that the following works:
+printf("%d\n", 0[x_array]); // => Prints 20;
+printf("%d\n", 2[x_array]); // => Prints 18;
+
+// The above is equivalent to:
+printf("%d\n", *(0 + x_ptr));
+printf("%d\n", *(2 + x_ptr));
+
+// You can give a pointer a block of memory to use with malloc
+int* my_ptr = (int*) malloc(sizeof(int) * 20);
+for(xx=0; xx<20; xx++){
+    *(my_ptr + xx) = 20 - xx;
+} // Initialize memory to 20, 19, 18, 17... 2, 1 (as ints)
+
+// Dereferencing memory that you haven't allocated gives
+// unpredictable results
+printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what?
+
+// When you're done with a malloc'd block, you need to free it
+free(my_ptr);
+
+// Strings can be char arrays, but are usually represented as char
+// pointers:
+char* my_str = "This is my very own string";
+
+printf("%d\n", *my_str); // 84 (The ascii value of 'T')
+
+function_1();
+} // end main function
+
+///////////////////////////////////////
+// Functions
+///////////////////////////////////////
+
+// Function declaration syntax:
+// <return type> <function name>(<args>)
+
+int add_two_ints(int x1, int x2){
+    return x1 + x2; // Use return a return a value
+}
+
+/*
+Pointers are passed-by-reference (duh), so functions
+can mutate their values.
+
+Example: in-place string reversal
+*/
+
+// A void function returns no value
+void str_reverse(char* str_in){
+    char tmp;
+    int ii=0, len = strlen(str_in); // Strlen is part of the c standard library
+    for(ii=0; ii<len/2; ii++){
+        tmp = str_in[ii];
+        str_in[ii] = str_in[len - ii - 1]; // ii-th char from end
+        str_in[len - ii - 1] = tmp;
+    }
+}
+
+/*
+char c[] = "This is a test.";
+str_reverse(c);
+printf("%s\n", c); // => ".tset a si sihT"
+*/
+
+///////////////////////////////////////
+// User-defined types and structs
+///////////////////////////////////////
+
+// Typedefs can be used to create type aliases
+typedef int my_type;
+my_type my_type_var = 0;
+
+// Structs are just collections of data
+struct rectangle {
+    int width;
+    int height;
+};
+
+
+void function_1(){
+
+    struct rectangle my_rec;
+
+    // Access struct members with .
+    my_rec.width = 10;
+    my_rec.height = 20;
+
+    // You can declare pointers to structs
+    struct rectangle* my_rec_ptr = &my_rec;
+
+    // Use dereferencing to set struct pointer members...
+    (*my_rec_ptr).width = 30;
+
+    // ... or use the -> shorthand
+    my_rec_ptr->height = 10; // Same as (*my_rec_ptr).height = 10;
+}
+
+// You can apply a typedef to a struct for convenience
+typedef struct rectangle rect;
+
+int area(rect r){
+    return r.width * r.height;
+}
+
+```
+
+## Further Reading
+
+Best to find yourself a copy of [K&R, aka "The C Programming Language"](https://en.wikipedia.org/wiki/The_C_Programming_Language)
+
+Another good resource is [Learn C the hard way](http://c.learncodethehardway.org/book/)
+
+Other than that, Google is your friend.

clojure.html.markdown

@@ -12,6 +12,9 @@ state as it comes up.
 This combination allows it to handle concurrent processing very simply,
 and often automatically.
 
+(You need a version of Clojure 1.2 or newer)
+
+
 ```clojure
 ; Comments start with semicolons.
 

php.html.markdown

@@ -87,7 +87,7 @@ $sgl_quotes
 END; // Nowdoc syntax is available in PHP 5.3.0
 
 // Manipulation
-$concatenated = $sgl_quotes + $dbl_quotes;
+$concatenated = $sgl_quotes . $dbl_quotes;
 ```
 
 ### Compound
@@ -119,6 +119,8 @@ print('Hello World!'); // The same as echo
 
 // echo is actually a language construct, so you can drop the parentheses.
 echo 'Hello World!';
+print 'Hello World!'; // So is print
+
 echo 100;
 echo $variable;
 echo function_result();
@@ -135,12 +137,12 @@ echo function_result();
 ```php
 <?php
 
-$a = 1;
+$x = 1;
-$b = 2;
+$y = 2;
-$a = $b; // A now contains the same value sa $b
+$x = $y; // A now contains the same value sa $y
-$a =& $b;
+$x = &$y;
-// A now contains a reference to $b. Changing the value of
+// $x now contains a reference to $y. Changing the value of
-// $a will change the value of $b also, and vice-versa.
+// $x will change the value of $y also, and vice-versa.
 ```
 
 ### Comparison
@@ -148,15 +150,20 @@ $a =& $b;
 ```php
 <?php
 
+// These comparisons will always be true, even if the types aren't the same.
 $a == $b // TRUE if $a is equal to $b after type juggling.
-$a === $b // TRUE if $a is equal to $b, and they are of the same type.
 $a != $b // TRUE if $a is not equal to $b after type juggling.
 $a <> $b // TRUE if $a is not equal to $b after type juggling.
-$a !== $b // TRUE if $a is not equal to $b, or they are not of the same type.
 $a < $b    // TRUE if $a is strictly less than $b.
 $a > $b // TRUE if $a is strictly greater than $b.
 $a <= $b // TRUE if $a is less than or equal to $b.
 $a >= $b // TRUE if $a is greater than or equal to $b.
+
+// The following will only be true if the values match and are the same type.
+$a === $b // TRUE if $a is equal to $b, and they are of the same type.
+$a !== $b // TRUE if $a is not equal to $b, or they are not of the same type.
+1 == '1' // TRUE
+1 === '1' // FALSE
 ```
 
 ## [Type Juggling](http://www.php.net/manual/en/language.types.type-juggling.php)
@@ -176,7 +183,11 @@ echo $string + $string;
 $string = 'one';
 echo $string + $string;
 // Outputs 0 because the + operator cannot cast the string 'one' to a number
+```
 
+Type casting can be used to treat a variable as another type temporarily by using cast operators in parentheses.
+
+```php
 $boolean = (boolean) $integer; // $boolean is true
 
 $zero = 0;
@@ -222,9 +233,9 @@ if (/* test */) {
 ?>
 
 <?php if (/* test */): ?>
-<!-- Do something that isn't PHP -->
+This is displayed if the test is truthy.
 <?php else: ?>
-<!-- Do something default -->
+This is displayed otherwise.
 <?php endif; ?>
 ```
 
@@ -278,7 +289,6 @@ while ($i < 5) {
     if ($i == 3) {
         break; // Exit out of the while loop and continue.
     }
-    
     echo $i++;
 }
 
@@ -288,7 +298,6 @@ while ($i < 5) {
     if ($i == 3) {
         continue; // Skip this iteration of the loop
     }
-    
     echo $i++;
 }
 ```
@@ -325,8 +334,8 @@ number of letters, numbers, or underscores. There are three ways to declare func
 ```php
 <?php
 
-function my_function_name ($arg_1, $arg_2) { // $arg_1 and $arg_2 are required
+function my_function_name ($arg_1, $arg_2) {
-    // Do something with $arg_1 and $arg_2;
+    // $arg_1 and $arg_2 are required
 }
 
 // Functions may be nested to limit scope
@@ -335,7 +344,25 @@ function outer_function ($arg_1 = null) { // $arg_1 is optional
     }
 }
 
-// inner_function() does not exist and cannot be called until outer_function() is called
+// inner_function() does not exist and cannot be called until
+// outer_function() is called
+```
+
+This enables [currying](http://en.wikipedia.org/wiki/Currying) in PHP.
+
+```php
+function foo ($x, $y, $z) {
+  echo "$x - $y - $z";
+}
+
+function bar ($x, $y) {
+  return function ($z) use ($x, $y) {
+    foo($x, $y, $z);
+  };
+}
+
+$bar = bar('A', 'B');
+$bar('C');
 ```
 
 ### [Variable](http://www.php.net/manual/en/functions.variable-functions.php)
@@ -355,7 +382,11 @@ Similar to variable functions, functions may be anonymous.
 ```php
 <?php
 
-my_function(function () {
+function my_function($callback) {
+    $callback('My argument');
+}
+
+my_function(function ($my_argument) {
     // do something
 });
 
@@ -396,12 +427,10 @@ class MyClass {
     function myFunction() {
     }
 
-    function function youCannotOverrideMe()
+    final function youCannotOverrideMe() {
-    {
     }
 
-    public static function myStaticMethod()
+    public static function myStaticMethod() {
-    {
     }
 }
 
@@ -438,7 +467,8 @@ echo $x->property; // Will use the __get() method
 $x->property = 'Something'; // Will use the __set() method
 ```
 
-Classes can be abstract (using the ```abstract``` keyword), extend other classes (using the ```extends``` keyword) and implement interfaces (using the ```implements``` keyword). An interface is declared with the ```interface``` keyword.
+Classes can be abstract (using the ```abstract``` keyword), extend other classes (using the ```extends``` keyword) and
+implement interfaces (using the ```implements``` keyword). An interface is declared with the ```interface``` keyword.
 
 ```php
 <?php

python.html.markdown

@@ -26,7 +26,7 @@ to Python 2.x. Look for another tour of Python 3 soon!
 
 # Math is what you would expect
 1 + 1 #=> 2
-8 - 1 #=> 9
+8 - 1 #=> 7
 10 * 2 #=> 20
 35 / 5 #=> 7
 
@@ -49,11 +49,24 @@ False
 not True #=> False
 not False #=> True
 
-
 # Equality is ==
 1 == 1 #=> True
 2 == 1 #=> False
 
+# Inequality is !=
+1 != 1 #=> False
+2 != 1 #=> True
+
+# More comparisons
+1 < 10 #=> True
+1 > 10 #=> False
+2 <= 2 #=> True
+2 >= 2 #=> True
+
+# Comparisons can be chained  !
+1 < 2 < 3 #=> True
+2 < 3 < 2 #=> False
+
 # Strings are created with " or '
 "This is a string."
 'This is also a string.'
@@ -81,8 +94,15 @@ some_var = 5    # Convention is to use lower_case_with_underscores
 some_var #=> 5
 
 # Accessing a previously unassigned variable is an exception
-some_other_var  # Will raise a NameError
+try:
+    some_other_var
+except NameError:
+    print "Raises a name error"
 
+# Conditional Expressions can be used when assigning
+some_var = a if a > b else b
+# If a is greater than b, then a is assigned to some_var.
+# Otherwise b is assigned to some_var.
 
 # Lists store sequences
 li = []
@@ -102,11 +122,16 @@ li.append(3)    # li is now [1, 2, 4, 3] again.
 # Access a list like you would any array
 li[0] #=> 1
 # Look at the last element
-li[-1] #=> 4
+li[-1] #=> 3
-# Looking out of bounds is an IndexError
-li[4] # Raises an IndexError
 
-# You can look at ranges with slice syntax. It's an closed/open range for you mathy types.
+# Looking out of bounds is an IndexError
+try:
+    li[4] # Raises an IndexError
+except IndexError:
+    print "Raises an IndexError"
+
+# You can look at ranges with slice syntax.
+# (It's a closed/open range for you mathy types.)
 li[1:3] #=> [2, 4]
 # Omit the beginning
 li[:3] #=> [1, 2, 4]
@@ -131,7 +156,10 @@ len(li) #=> 6
 # Tuples are like lists but are immutable.
 tup = (1, 2, 3)
 tup[0] #=> 1
+try:
     tup[0] = 3  # Raises a TypeError
+except TypeError:
+    print "Tuples cannot be mutated."
 
 # You can do all those list thingies on tuples too
 len(tup) #=> 3
@@ -143,7 +171,7 @@ tup[:2] #=> (1, 2)
 a, b, c = (1, 2, 3)     # a is now 1, b is now 2 and c is now 3
 # Tuples are created by default if you leave out the parentheses
 d, e, f = 4, 5, 6
-# Now look how easy it is to swap to values
+# Now look how easy it is to swap two values
 e, d = d, e     # d is now 5 and e is now 4
 
 
@@ -168,6 +196,21 @@ filled_dict.values() #=> [3, 2, 1]
 "one" in filled_dict #=> True
 1 in filled_dict #=> False
 
+# Trying to look up a non-existing key will raise a KeyError
+filled_dict["four"] #=> KeyError
+
+# Use get method to avoid the KeyError
+filled_dict.get("one") #=> 1
+filled_dict.get("four") #=> None
+
+# The get method supports a default argument when the value is missing
+filled_dict.get("one", 4) #=> 1
+filled_dict.get("four", 4) #=> 4
+
+# Setdefault method is a safe way to add new key-value pair into dictionary
+filled_dict.setdefault("five", 5) #filled_dict["five"] is set to 5
+filled_dict.setdefault("five", 6) #filled_dict["five"] is still 5
+
 
 # Sets store ... well sets
 empty_set = set()
@@ -232,11 +275,20 @@ while x < 4:
     x += 1  # Shorthand for x = x + 1
 
 # Handle exceptions with a try/except block
+
+# Works on Python 2.6 and up:
 try:
-    raise IndexError("This is an index error")  # Use raise to raise an error
+    # Use raise to raise an error
+    raise IndexError("This is an index error")
 except IndexError as e:
     pass    # Pass is just a no-op. Usually you would do recovery here.
 
+# Works for Python 2.7 and down:
+try:
+    raise IndexError("This is an index error")
+except IndexError, e: # No "as", comma instead
+    pass
+
 
 ####################################################
 ## 4. Functions
@@ -252,20 +304,38 @@ add(5, 6) #=> 11 and prints out "x is 5 and y is 6"
 # Another way to call functions is with keyword arguments
 add(y=6, x=5)   # Keyword arguments can arrive in any order.
 
-# You can define functions that take a variable number of positional arguments
+# You can define functions that take a variable number of
+# positional arguments
 def varargs(*args):
     return args
 
 varargs(1, 2, 3) #=> (1,2,3)
 
 
-# You can define functions that take a variable number of keyword arguments
+# You can define functions that take a variable number of
+# keyword arguments, as well
 def keyword_args(**kwargs):
     return kwargs
 
 # Let's call it to see what happens
 keyword_args(big="foot", loch="ness") #=> {"big": "foot", "loch": "ness"}
 
+# You can do both at once, if you like
+def all_the_args(*args, **kwargs):
+    print args
+    print kwargs
+"""
+all_the_args(1, 2, a=3, b=4) prints:
+    [1, 2]
+    {"a": 3, "b": 4}
+"""
+
+# You can also use * and ** when calling a function
+args = (1, 2, 3, 4)
+kwargs = {"a": 3, "b": 4}
+foo(*args) # equivalent to foo(1, 2, 3, 4)
+foo(**kwargs) # equivalent to foo(a=3, b=4)
+foo(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)
 
 # Python has first class functions
 def create_adder(x):
@@ -273,7 +343,7 @@ def create_adder(x):
         return x + y
     return adder
 
-add_10 = create_adder(10):
+add_10 = create_adder(10)
 add_10(3) #=> 13
 
 # There are also anonymous functions
@@ -329,9 +399,11 @@ print j.say("hello")  #prints out "Joel: hello"
 i.get_species() #=> "H. sapiens"
 
 # Change the shared attribute
-i.species = "H. neanderthalensis"
+Human.species = "H. neanderthalensis"
 i.get_species() #=> "H. neanderthalensis"
 j.get_species() #=> "H. neanderthalensis"
 
 # Call the static method
 Human.grunt() #=> "*grunt*"
+```
+