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0001 <!DOCTYPE html> 0002 <html><head> 0003 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/> 0004 <title>learnelixir.exs</title> 0005 <meta name="generator" content="KF5::SyntaxHighlighting - Definition (Elixir) - Theme (Breeze Light)"/> 0006 </head><body style="background-color:#ffffff;color:#1f1c1b"><pre> 0007 <span style="color:#898887;"># Original: https://learnxinyminutes.com/docs/elixir/</span> 0008 0009 <span style="color:#898887;"># Single line comments start with a number symbol.</span> 0010 0011 <span style="color:#898887;"># There's no multi-line comment,</span> 0012 <span style="color:#898887;"># but you can stack multiple comments.</span> 0013 0014 <span style="color:#898887;"># To use the elixir shell use the `iex` command.</span> 0015 <span style="color:#898887;"># Compile your modules with the `elixirc` command.</span> 0016 0017 <span style="color:#898887;"># Both should be in your path if you installed elixir correctly.</span> 0018 0019 <span style="color:#898887;">## ---------------------------</span> 0020 <span style="color:#898887;">## -- Basic types</span> 0021 <span style="color:#898887;">## ---------------------------</span> 0022 0023 <span style="color:#898887;"># There are numbers</span> 0024 <span style="color:#b08000;">3</span> <span style="color:#898887;"># integer</span> 0025 <span style="color:#b08000;">0x1F</span> <span style="color:#898887;"># integer</span> 0026 <span style="color:#b08000;">3.0</span> <span style="color:#898887;"># float</span> 0027 0028 <span style="color:#898887;"># Atoms, that are literals, a constant with name. They start with `:`.</span> 0029 <span style="color:#0057ae;">:hello</span> <span style="color:#898887;"># atom</span> 0030 0031 <span style="color:#898887;"># Tuples that are stored contiguously in memory.</span> 0032 <span style="color:#644a9b;">{</span><span style="color:#b08000;">1</span>,<span style="color:#b08000;">2</span>,<span style="color:#b08000;">3</span><span style="color:#644a9b;">}</span> <span style="color:#898887;"># tuple</span> 0033 0034 <span style="color:#898887;"># We can access a tuple element with the `elem` function:</span> 0035 elem<span style="color:#644a9b;">({</span><span style="color:#b08000;">1</span>, <span style="color:#b08000;">2</span>, <span style="color:#b08000;">3</span><span style="color:#644a9b;">}</span>, <span style="color:#b08000;">0</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 1</span> 0036 0037 <span style="color:#898887;"># Lists that are implemented as linked lists.</span> 0038 <span style="color:#006e28;">[</span><span style="color:#b08000;">1</span>,<span style="color:#b08000;">2</span>,<span style="color:#b08000;">3</span><span style="color:#006e28;">]</span> <span style="color:#898887;"># list</span> 0039 0040 <span style="color:#898887;"># We can access the head and tail of a list as follows:</span> 0041 <span style="color:#006e28;">[</span>head <span style="color:#ca60ca;">|</span> tail<span style="color:#006e28;">]</span> <span style="color:#ca60ca;">=</span> <span style="color:#006e28;">[</span><span style="color:#b08000;">1</span>,<span style="color:#b08000;">2</span>,<span style="color:#b08000;">3</span><span style="color:#006e28;">]</span> 0042 head <span style="color:#898887;">#=> 1</span> 0043 tail <span style="color:#898887;">#=> [2,3]</span> 0044 0045 <span style="color:#898887;"># In elixir, just like in Erlang, the `=` denotes pattern matching and</span> 0046 <span style="color:#898887;"># not an assignment.</span> 0047 <span style="color:#898887;">#</span> 0048 <span style="color:#898887;"># This means that the left-hand side (pattern) is matched against a</span> 0049 <span style="color:#898887;"># right-hand side.</span> 0050 <span style="color:#898887;">#</span> 0051 <span style="color:#898887;"># This is how the above example of accessing the head and tail of a list works.</span> 0052 0053 <span style="color:#898887;"># A pattern match will error when the sides don't match, in this example</span> 0054 <span style="color:#898887;"># the tuples have different sizes.</span> 0055 <span style="color:#898887;"># {a, b, c} = {1, 2} #=> ** (MatchError) no match of right hand side value: {1,2}</span> 0056 0057 <span style="color:#898887;"># There are also binaries</span> 0058 <span style="color:#ca60ca;"><<</span><span style="color:#b08000;">1</span>,<span style="color:#b08000;">2</span>,<span style="color:#b08000;">3</span><span style="color:#ca60ca;">>></span> <span style="color:#898887;"># binary</span> 0059 0060 <span style="color:#898887;"># Strings and char lists</span> 0061 <span style="color:#bf0303;">"hello"</span> <span style="color:#898887;"># string</span> 0062 <span style="color:#e31616;">'hello'</span> <span style="color:#898887;"># char list</span> 0063 0064 <span style="color:#898887;"># Multi-line strings</span> 0065 <span style="color:#bf0303;">"""</span> 0066 <span style="color:#bf0303;">I'm a multi-line</span> 0067 <span style="color:#bf0303;">string.</span> 0068 <span style="color:#bf0303;">"""</span> 0069 <span style="color:#898887;">#=> "I'm a multi-line\nstring.\n"</span> 0070 0071 <span style="color:#898887;"># Strings are all encoded in UTF-8:</span> 0072 <span style="color:#bf0303;">"héllò"</span> <span style="color:#898887;">#=> "héllò"</span> 0073 0074 <span style="color:#898887;"># Strings are really just binaries, and char lists are just lists.</span> 0075 <span style="color:#ca60ca;"><<</span>?a, ?b, ?c<span style="color:#ca60ca;">>></span> <span style="color:#898887;">#=> "abc"</span> 0076 <span style="color:#006e28;">[</span>?a, ?b, ?c<span style="color:#006e28;">]</span> <span style="color:#898887;">#=> 'abc'</span> 0077 0078 <span style="color:#898887;"># `?a` in elixir returns the ASCII integer for the letter `a`</span> 0079 ?a <span style="color:#898887;">#=> 97</span> 0080 0081 <span style="color:#898887;"># To concatenate lists use `++`, for binaries use `<>`</span> 0082 <span style="color:#006e28;">[</span><span style="color:#b08000;">1</span>,<span style="color:#b08000;">2</span>,<span style="color:#b08000;">3</span><span style="color:#006e28;">]</span> <span style="color:#ca60ca;">++</span> <span style="color:#006e28;">[</span><span style="color:#b08000;">4</span>,<span style="color:#b08000;">5</span><span style="color:#006e28;">]</span> <span style="color:#898887;">#=> [1,2,3,4,5]</span> 0083 <span style="color:#e31616;">'hello '</span> <span style="color:#ca60ca;">++</span> <span style="color:#e31616;">'world'</span> <span style="color:#898887;">#=> 'hello world'</span> 0084 0085 <span style="color:#ca60ca;"><<</span><span style="color:#b08000;">1</span>,<span style="color:#b08000;">2</span>,<span style="color:#b08000;">3</span><span style="color:#ca60ca;">>></span> <span style="color:#ca60ca;"><></span> <span style="color:#ca60ca;"><<</span><span style="color:#b08000;">4</span>,<span style="color:#b08000;">5</span><span style="color:#ca60ca;">>></span> <span style="color:#898887;">#=> <<1,2,3,4,5>></span> 0086 <span style="color:#bf0303;">"hello "</span> <span style="color:#ca60ca;"><></span> <span style="color:#bf0303;">"world"</span> <span style="color:#898887;">#=> "hello world"</span> 0087 0088 <span style="color:#898887;"># Ranges are represented as `start..end` (both inclusive)</span> 0089 <span style="color:#b08000;">1</span><span style="color:#ca60ca;">..</span><span style="color:#b08000;">10</span> <span style="color:#898887;">#=> 1..10</span> 0090 lower<span style="color:#ca60ca;">..</span>upper <span style="color:#ca60ca;">=</span> <span style="color:#b08000;">1</span><span style="color:#ca60ca;">..</span><span style="color:#b08000;">10</span> <span style="color:#898887;"># Can use pattern matching on ranges as well</span> 0091 <span style="color:#006e28;">[</span>lower, upper<span style="color:#006e28;">]</span> <span style="color:#898887;">#=> [1, 10]</span> 0092 0093 <span style="color:#898887;">## ---------------------------</span> 0094 <span style="color:#898887;">## -- Operators</span> 0095 <span style="color:#898887;">## ---------------------------</span> 0096 0097 <span style="color:#898887;"># Some math</span> 0098 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">+</span> <span style="color:#b08000;">1</span> <span style="color:#898887;">#=> 2</span> 0099 <span style="color:#b08000;">10</span> <span style="color:#ca60ca;">-</span> <span style="color:#b08000;">5</span> <span style="color:#898887;">#=> 5</span> 0100 <span style="color:#b08000;">5</span> <span style="color:#ca60ca;">*</span> <span style="color:#b08000;">2</span> <span style="color:#898887;">#=> 10</span> 0101 <span style="color:#b08000;">10</span> <span style="color:#ca60ca;">/</span> <span style="color:#b08000;">2</span> <span style="color:#898887;">#=> 5.0</span> 0102 0103 <span style="color:#898887;"># In elixir the operator `/` always returns a float.</span> 0104 0105 <span style="color:#898887;"># To do integer division use `div`</span> 0106 div<span style="color:#644a9b;">(</span><span style="color:#b08000;">10</span>, <span style="color:#b08000;">2</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 5</span> 0107 0108 <span style="color:#898887;"># To get the division remainder use `rem`</span> 0109 rem<span style="color:#644a9b;">(</span><span style="color:#b08000;">10</span>, <span style="color:#b08000;">3</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 1</span> 0110 0111 <span style="color:#898887;"># There are also boolean operators: `or`, `and` and `not`.</span> 0112 <span style="color:#898887;"># These operators expect a boolean as their first argument.</span> 0113 <span style="color:#aa5500;">true</span> <span style="font-weight:bold;">and</span> <span style="color:#aa5500;">true</span> <span style="color:#898887;">#=> true</span> 0114 <span style="color:#aa5500;">false</span> <span style="font-weight:bold;">or</span> <span style="color:#aa5500;">true</span> <span style="color:#898887;">#=> true</span> 0115 <span style="color:#898887;"># 1 and true #=> ** (ArgumentError) argument error</span> 0116 0117 <span style="color:#898887;"># Elixir also provides `||`, `&&` and `!` which accept arguments of any type.</span> 0118 <span style="color:#898887;"># All values except `false` and `nil` will evaluate to true.</span> 0119 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">||</span> <span style="color:#aa5500;">true</span> <span style="color:#898887;">#=> 1</span> 0120 <span style="color:#aa5500;">false</span> <span style="color:#ca60ca;">&&</span> <span style="color:#b08000;">1</span> <span style="color:#898887;">#=> false</span> 0121 <span style="color:#aa5500;">nil</span> <span style="color:#ca60ca;">&&</span> <span style="color:#b08000;">20</span> <span style="color:#898887;">#=> nil</span> 0122 !true <span style="color:#898887;">#=> false</span> 0123 0124 <span style="color:#898887;"># For comparisons we have: `==`, `!=`, `===`, `!==`, `<=`, `>=`, `<` and `>`</span> 0125 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">==</span> <span style="color:#b08000;">1</span> <span style="color:#898887;">#=> true</span> 0126 <span style="color:#b08000;">1</span><span style="color:#ca60ca;"> !=</span> <span style="color:#b08000;">1</span> <span style="color:#898887;">#=> false</span> 0127 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;"><</span> <span style="color:#b08000;">2</span> <span style="color:#898887;">#=> true</span> 0128 0129 <span style="color:#898887;"># `===` and `!==` are more strict when comparing integers and floats:</span> 0130 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">==</span> <span style="color:#b08000;">1.0</span> <span style="color:#898887;">#=> true</span> 0131 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">===</span> <span style="color:#b08000;">1.0</span> <span style="color:#898887;">#=> false</span> 0132 0133 <span style="color:#898887;"># We can also compare two different data types:</span> 0134 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;"><</span> <span style="color:#0057ae;">:hello</span> <span style="color:#898887;">#=> true</span> 0135 0136 <span style="color:#898887;"># The overall sorting order is defined below:</span> 0137 <span style="color:#898887;"># number < atom < reference < functions < port < pid < tuple < list < bit string</span> 0138 0139 <span style="color:#898887;"># To quote Joe Armstrong on this: "The actual order is not important,</span> 0140 <span style="color:#898887;"># but that a total ordering is well defined is important."</span> 0141 0142 <span style="color:#898887;">## ---------------------------</span> 0143 <span style="color:#898887;">## -- Control Flow</span> 0144 <span style="color:#898887;">## ---------------------------</span> 0145 0146 <span style="color:#898887;"># `if` expression</span> 0147 <span style="font-weight:bold;">if</span> <span style="color:#aa5500;">false</span> <span style="font-weight:bold;">do</span> 0148 <span style="color:#bf0303;">"This will never be seen"</span> 0149 <span style="font-weight:bold;">else</span> 0150 <span style="color:#bf0303;">"This will"</span> 0151 <span style="font-weight:bold;">end</span> 0152 0153 <span style="color:#898887;"># There's also `unless`</span> 0154 <span style="font-weight:bold;">unless</span> <span style="color:#aa5500;">true</span> <span style="font-weight:bold;">do</span> 0155 <span style="color:#bf0303;">"This will never be seen"</span> 0156 <span style="font-weight:bold;">else</span> 0157 <span style="color:#bf0303;">"This will"</span> 0158 <span style="font-weight:bold;">end</span> 0159 0160 <span style="color:#898887;"># Remember pattern matching? Many control-flow structures in elixir rely on it.</span> 0161 0162 <span style="color:#898887;"># `case` allows us to compare a value against many patterns:</span> 0163 <span style="font-weight:bold;">case</span> <span style="color:#644a9b;">{</span><span style="color:#0057ae;">:one</span>, <span style="color:#0057ae;">:two</span><span style="color:#644a9b;">}</span> <span style="font-weight:bold;">do</span> 0164 <span style="color:#644a9b;">{</span><span style="color:#0057ae;">:four</span>, <span style="color:#0057ae;">:five</span><span style="color:#644a9b;">}</span> <span style="color:#ca60ca;">-></span> 0165 <span style="color:#bf0303;">"This won't match"</span> 0166 <span style="color:#644a9b;">{</span><span style="color:#0057ae;">:one</span>, x<span style="color:#644a9b;">}</span> <span style="color:#ca60ca;">-></span> 0167 <span style="color:#bf0303;">"This will match and bind `x` to `:two`"</span> 0168 _ <span style="color:#ca60ca;">-></span> 0169 <span style="color:#bf0303;">"This will match any value"</span> 0170 <span style="font-weight:bold;">end</span> 0171 0172 <span style="color:#898887;"># It's common to bind the value to `_` if we don't need it.</span> 0173 <span style="color:#898887;"># For example, if only the head of a list matters to us:</span> 0174 <span style="color:#006e28;">[</span>head <span style="color:#ca60ca;">|</span> _<span style="color:#006e28;">]</span> <span style="color:#ca60ca;">=</span> <span style="color:#006e28;">[</span><span style="color:#b08000;">1</span>,<span style="color:#b08000;">2</span>,<span style="color:#b08000;">3</span><span style="color:#006e28;">]</span> 0175 head <span style="color:#898887;">#=> 1</span> 0176 0177 <span style="color:#898887;"># For better readability we can do the following:</span> 0178 <span style="color:#006e28;">[</span>head <span style="color:#ca60ca;">|</span> _tail<span style="color:#006e28;">]</span> <span style="color:#ca60ca;">=</span> <span style="color:#006e28;">[</span><span style="color:#0057ae;">:a</span>, <span style="color:#0057ae;">:b</span>, <span style="color:#0057ae;">:c</span><span style="color:#006e28;">]</span> 0179 head <span style="color:#898887;">#=> :a</span> 0180 0181 <span style="color:#898887;"># `cond` lets us check for many conditions at the same time.</span> 0182 <span style="color:#898887;"># Use `cond` instead of nesting many `if` expressions.</span> 0183 <span style="font-weight:bold;">cond</span> <span style="font-weight:bold;">do</span> 0184 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">+</span> <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">==</span> <span style="color:#b08000;">3</span> <span style="color:#ca60ca;">-></span> 0185 <span style="color:#bf0303;">"I will never be seen"</span> 0186 <span style="color:#b08000;">2</span> <span style="color:#ca60ca;">*</span> <span style="color:#b08000;">5</span> <span style="color:#ca60ca;">==</span> <span style="color:#b08000;">12</span> <span style="color:#ca60ca;">-></span> 0187 <span style="color:#bf0303;">"Me neither"</span> 0188 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">+</span> <span style="color:#b08000;">2</span> <span style="color:#ca60ca;">==</span> <span style="color:#b08000;">3</span> <span style="color:#ca60ca;">-></span> 0189 <span style="color:#bf0303;">"But I will"</span> 0190 <span style="font-weight:bold;">end</span> 0191 0192 <span style="color:#898887;"># It is common to set the last condition equal to `true`, which will always match.</span> 0193 <span style="font-weight:bold;">cond</span> <span style="font-weight:bold;">do</span> 0194 <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">+</span> <span style="color:#b08000;">1</span> <span style="color:#ca60ca;">==</span> <span style="color:#b08000;">3</span> <span style="color:#ca60ca;">-></span> 0195 <span style="color:#bf0303;">"I will never be seen"</span> 0196 <span style="color:#b08000;">2</span> <span style="color:#ca60ca;">*</span> <span style="color:#b08000;">5</span> <span style="color:#ca60ca;">==</span> <span style="color:#b08000;">12</span> <span style="color:#ca60ca;">-></span> 0197 <span style="color:#bf0303;">"Me neither"</span> 0198 <span style="color:#aa5500;">true</span> <span style="color:#ca60ca;">-></span> 0199 <span style="color:#bf0303;">"But I will (this is essentially an else)"</span> 0200 <span style="font-weight:bold;">end</span> 0201 0202 <span style="color:#898887;"># `try/catch` is used to catch values that are thrown, it also supports an</span> 0203 <span style="color:#898887;"># `after` clause that is invoked whether or not a value is caught.</span> 0204 <span style="font-weight:bold;">try</span> <span style="font-weight:bold;">do</span> 0205 <span style="font-weight:bold;">throw</span><span style="color:#644a9b;">(</span><span style="color:#0057ae;">:hello</span><span style="color:#644a9b;">)</span> 0206 <span style="font-weight:bold;">catch</span> 0207 message <span style="color:#ca60ca;">-></span> <span style="color:#bf0303;">"Got </span><span style="color:#006e28;">#{</span>message<span style="color:#006e28;">}</span><span style="color:#bf0303;">."</span> 0208 <span style="font-weight:bold;">after</span> 0209 <span style="color:#aa5500;">IO</span><span style="color:#ca60ca;">.</span>puts<span style="color:#644a9b;">(</span><span style="color:#bf0303;">"I'm the after clause."</span><span style="color:#644a9b;">)</span> 0210 <span style="font-weight:bold;">end</span> 0211 <span style="color:#898887;">#=> I'm the after clause</span> 0212 <span style="color:#898887;"># "Got :hello"</span> 0213 0214 <span style="color:#898887;">## ---------------------------</span> 0215 <span style="color:#898887;">## -- Modules and Functions</span> 0216 <span style="color:#898887;">## ---------------------------</span> 0217 0218 <span style="color:#898887;"># Anonymous functions (notice the dot)</span> 0219 square <span style="color:#ca60ca;">=</span> <span style="font-weight:bold;">fn</span><span style="color:#644a9b;">(</span>x<span style="color:#644a9b;">)</span> <span style="color:#ca60ca;">-></span> x <span style="color:#ca60ca;">*</span> x <span style="font-weight:bold;">end</span> 0220 square<span style="color:#ca60ca;">.</span><span style="color:#644a9b;">(</span><span style="color:#b08000;">5</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 25</span> 0221 0222 <span style="color:#898887;"># They also accept many clauses and guards.</span> 0223 <span style="color:#898887;"># Guards let you fine tune pattern matching,</span> 0224 <span style="color:#898887;"># they are indicated by the `when` keyword:</span> 0225 f <span style="color:#ca60ca;">=</span> <span style="font-weight:bold;">fn</span> 0226 x, y <span style="font-weight:bold;">when</span> x <span style="color:#ca60ca;">></span> <span style="color:#b08000;">0</span> <span style="color:#ca60ca;">-></span> x <span style="color:#ca60ca;">+</span> y 0227 x, y <span style="color:#ca60ca;">-></span> x <span style="color:#ca60ca;">*</span> y 0228 <span style="font-weight:bold;">end</span> 0229 0230 f<span style="color:#ca60ca;">.</span><span style="color:#644a9b;">(</span><span style="color:#b08000;">1</span>, <span style="color:#b08000;">3</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 4</span> 0231 f<span style="color:#ca60ca;">.</span><span style="color:#644a9b;">(</span><span style="color:#ca60ca;">-</span><span style="color:#b08000;">1</span>, <span style="color:#b08000;">3</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> -3</span> 0232 0233 <span style="color:#898887;"># Elixir also provides many built-in functions.</span> 0234 <span style="color:#898887;"># These are available in the current scope.</span> 0235 is_number<span style="color:#644a9b;">(</span><span style="color:#b08000;">10</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> true</span> 0236 is_list<span style="color:#644a9b;">(</span><span style="color:#bf0303;">"hello"</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> false</span> 0237 elem<span style="color:#644a9b;">({</span><span style="color:#b08000;">1</span>,<span style="color:#b08000;">2</span>,<span style="color:#b08000;">3</span><span style="color:#644a9b;">}</span>, <span style="color:#b08000;">0</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 1</span> 0238 0239 <span style="color:#898887;"># You can group several functions into a module. Inside a module use `def`</span> 0240 <span style="color:#898887;"># to define your functions.</span> 0241 <span style="font-weight:bold;">defmodule</span> <span style="color:#aa5500;">Math</span> <span style="font-weight:bold;">do</span> 0242 <span style="font-weight:bold;">def</span> sum<span style="color:#644a9b;">(</span>a, b<span style="color:#644a9b;">)</span> <span style="font-weight:bold;">do</span> 0243 a <span style="color:#ca60ca;">+</span> b 0244 <span style="font-weight:bold;">end</span> 0245 0246 <span style="font-weight:bold;">def</span> square<span style="color:#644a9b;">(</span>x<span style="color:#644a9b;">)</span> <span style="font-weight:bold;">do</span> 0247 x <span style="color:#ca60ca;">*</span> x 0248 <span style="font-weight:bold;">end</span> 0249 <span style="font-weight:bold;">end</span> 0250 0251 <span style="color:#aa5500;">Math</span><span style="color:#ca60ca;">.</span>sum<span style="color:#644a9b;">(</span><span style="color:#b08000;">1</span>, <span style="color:#b08000;">2</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 3</span> 0252 <span style="color:#aa5500;">Math</span><span style="color:#ca60ca;">.</span>square<span style="color:#644a9b;">(</span><span style="color:#b08000;">3</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 9</span> 0253 0254 <span style="color:#898887;"># To compile our simple Math module save it as `math.ex` and use `elixirc`</span> 0255 <span style="color:#898887;"># in your terminal: elixirc math.ex</span> 0256 0257 <span style="color:#898887;"># Inside a module we can define functions with `def` and private functions with `defp`.</span> 0258 <span style="color:#898887;"># A function defined with `def` is available to be invoked from other modules,</span> 0259 <span style="color:#898887;"># a private function can only be invoked locally.</span> 0260 <span style="font-weight:bold;">defmodule</span> <span style="color:#aa5500;">PrivateMath</span> <span style="font-weight:bold;">do</span> 0261 <span style="font-weight:bold;">def</span> sum<span style="color:#644a9b;">(</span>a, b<span style="color:#644a9b;">)</span> <span style="font-weight:bold;">do</span> 0262 do_sum<span style="color:#644a9b;">(</span>a, b<span style="color:#644a9b;">)</span> 0263 <span style="font-weight:bold;">end</span> 0264 0265 <span style="font-weight:bold;">defp</span> do_sum<span style="color:#644a9b;">(</span>a, b<span style="color:#644a9b;">)</span> <span style="font-weight:bold;">do</span> 0266 a <span style="color:#ca60ca;">+</span> b 0267 <span style="font-weight:bold;">end</span> 0268 <span style="font-weight:bold;">end</span> 0269 0270 <span style="color:#aa5500;">PrivateMath</span><span style="color:#ca60ca;">.</span>sum<span style="color:#644a9b;">(</span><span style="color:#b08000;">1</span>, <span style="color:#b08000;">2</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 3</span> 0271 <span style="color:#898887;"># PrivateMath.do_sum(1, 2) #=> ** (UndefinedFunctionError)</span> 0272 0273 <span style="color:#898887;"># Function declarations also support guards and multiple clauses:</span> 0274 <span style="font-weight:bold;">defmodule</span> <span style="color:#aa5500;">Geometry</span> <span style="font-weight:bold;">do</span> 0275 <span style="font-weight:bold;">def</span> area<span style="color:#644a9b;">({</span><span style="color:#0057ae;">:rectangle</span>, w, h<span style="color:#644a9b;">})</span> <span style="font-weight:bold;">do</span> 0276 w <span style="color:#ca60ca;">*</span> h 0277 <span style="font-weight:bold;">end</span> 0278 0279 <span style="font-weight:bold;">def</span> area<span style="color:#644a9b;">({</span><span style="color:#0057ae;">:circle</span>, r<span style="color:#644a9b;">})</span> <span style="font-weight:bold;">when</span> is_number<span style="color:#644a9b;">(</span>r<span style="color:#644a9b;">)</span> <span style="font-weight:bold;">do</span> 0280 <span style="color:#b08000;">3.14</span> <span style="color:#ca60ca;">*</span> r <span style="color:#ca60ca;">*</span> r 0281 <span style="font-weight:bold;">end</span> 0282 <span style="font-weight:bold;">end</span> 0283 0284 <span style="color:#aa5500;">Geometry</span><span style="color:#ca60ca;">.</span>area<span style="color:#644a9b;">({</span><span style="color:#0057ae;">:rectangle</span>, <span style="color:#b08000;">2</span>, <span style="color:#b08000;">3</span><span style="color:#644a9b;">})</span> <span style="color:#898887;">#=> 6</span> 0285 <span style="color:#aa5500;">Geometry</span><span style="color:#ca60ca;">.</span>area<span style="color:#644a9b;">({</span><span style="color:#0057ae;">:circle</span>, <span style="color:#b08000;">3</span><span style="color:#644a9b;">})</span> <span style="color:#898887;">#=> 28.25999999999999801048</span> 0286 <span style="color:#898887;"># Geometry.area({:circle, "not_a_number"})</span> 0287 <span style="color:#898887;">#=> ** (FunctionClauseError) no function clause matching in Geometry.area/1</span> 0288 0289 <span style="color:#898887;"># Due to immutability, recursion is a big part of elixir</span> 0290 <span style="font-weight:bold;">defmodule</span> <span style="color:#aa5500;">Recursion</span> <span style="font-weight:bold;">do</span> 0291 <span style="font-weight:bold;">def</span> sum_list<span style="color:#644a9b;">(</span><span style="color:#006e28;">[</span>head <span style="color:#ca60ca;">|</span> tail<span style="color:#006e28;">]</span>, acc<span style="color:#644a9b;">)</span> <span style="font-weight:bold;">do</span> 0292 sum_list<span style="color:#644a9b;">(</span>tail, acc <span style="color:#ca60ca;">+</span> head<span style="color:#644a9b;">)</span> 0293 <span style="font-weight:bold;">end</span> 0294 0295 <span style="font-weight:bold;">def</span> sum_list<span style="color:#644a9b;">(</span><span style="color:#006e28;">[]</span>, acc<span style="color:#644a9b;">)</span> <span style="font-weight:bold;">do</span> 0296 acc 0297 <span style="font-weight:bold;">end</span> 0298 <span style="font-weight:bold;">end</span> 0299 0300 <span style="color:#aa5500;">Recursion</span><span style="color:#ca60ca;">.</span>sum_list<span style="color:#644a9b;">(</span><span style="color:#006e28;">[</span><span style="color:#b08000;">1</span>,<span style="color:#b08000;">2</span>,<span style="color:#b08000;">3</span><span style="color:#006e28;">]</span>, <span style="color:#b08000;">0</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 6</span> 0301 0302 <span style="color:#898887;"># Elixir modules support attributes, there are built-in attributes and you</span> 0303 <span style="color:#898887;"># may also add custom ones.</span> 0304 <span style="font-weight:bold;">defmodule</span> <span style="color:#aa5500;">MyMod</span> <span style="font-weight:bold;">do</span> 0305 <span style="color:#006e28;">@moduledoc """</span> 0306 <span style="color:#898887;"> This is a built-in attribute on a example module.</span> 0307 <span style="color:#898887;"> </span><span style="color:#006e28;">"""</span> 0308 0309 <span style="color:#006e28;">@my_data</span> <span style="color:#b08000;">100</span> <span style="color:#898887;"># This is a custom attribute.</span> 0310 <span style="color:#aa5500;">IO</span><span style="color:#ca60ca;">.</span>inspect<span style="color:#644a9b;">(</span><span style="color:#006e28;">@my_data</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> 100</span> 0311 <span style="font-weight:bold;">end</span> 0312 0313 <span style="color:#898887;">## ---------------------------</span> 0314 <span style="color:#898887;">## -- Structs and Exceptions</span> 0315 <span style="color:#898887;">## ---------------------------</span> 0316 0317 <span style="color:#898887;"># Structs are extensions on top of maps that bring default values,</span> 0318 <span style="color:#898887;"># compile-time guarantees and polymorphism into Elixir.</span> 0319 <span style="font-weight:bold;">defmodule</span> <span style="color:#aa5500;">Person</span> <span style="font-weight:bold;">do</span> 0320 <span style="font-weight:bold;">defstruct</span> <span style="color:#0057ae;">name:</span> <span style="color:#aa5500;">nil</span>, <span style="color:#0057ae;">age:</span> <span style="color:#b08000;">0</span>, <span style="color:#0057ae;">height:</span> <span style="color:#b08000;">0</span> 0321 <span style="font-weight:bold;">end</span> 0322 0323 joe_info <span style="color:#ca60ca;">=</span> %<span style="color:#aa5500;">Person</span><span style="color:#644a9b;">{</span> <span style="color:#0057ae;">name:</span> <span style="color:#bf0303;">"Joe"</span>, <span style="color:#0057ae;">age:</span> <span style="color:#b08000;">30</span>, <span style="color:#0057ae;">height:</span> <span style="color:#b08000;">180</span> <span style="color:#644a9b;">}</span> 0324 <span style="color:#898887;">#=> %Person{age: 30, height: 180, name: "Joe"}</span> 0325 0326 <span style="color:#898887;"># Access the value of name</span> 0327 joe_info<span style="color:#ca60ca;">.</span>name <span style="color:#898887;">#=> "Joe"</span> 0328 0329 <span style="color:#898887;"># Update the value of age</span> 0330 older_joe_info <span style="color:#ca60ca;">=</span> %<span style="color:#644a9b;">{</span> joe_info <span style="color:#ca60ca;">|</span> <span style="color:#0057ae;">age:</span> <span style="color:#b08000;">31</span> <span style="color:#644a9b;">}</span> 0331 <span style="color:#898887;">#=> %Person{age: 31, height: 180, name: "Joe"}</span> 0332 0333 <span style="color:#898887;"># The `try` block with the `rescue` keyword is used to handle exceptions</span> 0334 <span style="font-weight:bold;">try</span> <span style="font-weight:bold;">do</span> 0335 <span style="font-weight:bold;">raise</span> <span style="color:#bf0303;">"some error"</span> 0336 <span style="font-weight:bold;">rescue</span> 0337 <span style="color:#aa5500;">RuntimeError</span> <span style="color:#ca60ca;">-></span> <span style="color:#bf0303;">"rescued a runtime error"</span> 0338 _error <span style="color:#ca60ca;">-></span> <span style="color:#bf0303;">"this will rescue any error"</span> 0339 <span style="font-weight:bold;">end</span> 0340 <span style="color:#898887;">#=> "rescued a runtime error"</span> 0341 0342 <span style="color:#898887;"># All exceptions have a message</span> 0343 <span style="font-weight:bold;">try</span> <span style="font-weight:bold;">do</span> 0344 <span style="font-weight:bold;">raise</span> <span style="color:#bf0303;">"some error"</span> 0345 <span style="font-weight:bold;">rescue</span> 0346 x <span style="font-weight:bold;">in</span> <span style="color:#006e28;">[</span><span style="color:#aa5500;">RuntimeError</span><span style="color:#006e28;">]</span> <span style="color:#ca60ca;">-></span> 0347 x<span style="color:#ca60ca;">.</span>message 0348 <span style="font-weight:bold;">end</span> 0349 <span style="color:#898887;">#=> "some error"</span> 0350 0351 <span style="color:#898887;">## ---------------------------</span> 0352 <span style="color:#898887;">## -- Concurrency</span> 0353 <span style="color:#898887;">## ---------------------------</span> 0354 0355 <span style="color:#898887;"># Elixir relies on the actor model for concurrency. All we need to write</span> 0356 <span style="color:#898887;"># concurrent programs in elixir are three primitives: spawning processes,</span> 0357 <span style="color:#898887;"># sending messages and receiving messages.</span> 0358 0359 <span style="color:#898887;"># To start a new process we use the `spawn` function, which takes a function</span> 0360 <span style="color:#898887;"># as argument.</span> 0361 f <span style="color:#ca60ca;">=</span> <span style="font-weight:bold;">fn</span> <span style="color:#ca60ca;">-></span> <span style="color:#b08000;">2</span> <span style="color:#ca60ca;">*</span> <span style="color:#b08000;">2</span> <span style="font-weight:bold;">end</span> <span style="color:#898887;">#=> #Function<erl_eval.20.80484245></span> 0362 spawn<span style="color:#644a9b;">(</span>f<span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> #PID<0.40.0></span> 0363 0364 <span style="color:#898887;"># `spawn` returns a pid (process identifier), you can use this pid to send</span> 0365 <span style="color:#898887;"># messages to the process. To do message passing we use the `send` operator.</span> 0366 <span style="color:#898887;"># For all of this to be useful we need to be able to receive messages. This is</span> 0367 <span style="color:#898887;"># achieved with the `receive` mechanism:</span> 0368 0369 <span style="color:#898887;"># The `receive do` block is used to listen for messages and process</span> 0370 <span style="color:#898887;"># them when they are received. A `receive do` block will only</span> 0371 <span style="color:#898887;"># process one received message. In order to process multiple</span> 0372 <span style="color:#898887;"># messages, a function with a `receive do` block must recursively</span> 0373 <span style="color:#898887;"># call itself to get into the `receive do` block again.</span> 0374 0375 <span style="font-weight:bold;">defmodule</span> <span style="color:#aa5500;">Geometry</span> <span style="font-weight:bold;">do</span> 0376 <span style="font-weight:bold;">def</span> area_loop <span style="font-weight:bold;">do</span> 0377 <span style="font-weight:bold;">receive</span> <span style="font-weight:bold;">do</span> 0378 <span style="color:#644a9b;">{</span><span style="color:#0057ae;">:rectangle</span>, w, h<span style="color:#644a9b;">}</span> <span style="color:#ca60ca;">-></span> 0379 <span style="color:#aa5500;">IO</span><span style="color:#ca60ca;">.</span>puts<span style="color:#644a9b;">(</span><span style="color:#bf0303;">"Area = </span><span style="color:#006e28;">#{</span>w <span style="color:#ca60ca;">*</span> h<span style="color:#006e28;">}</span><span style="color:#bf0303;">"</span><span style="color:#644a9b;">)</span> 0380 area_loop<span style="color:#644a9b;">()</span> 0381 <span style="color:#644a9b;">{</span><span style="color:#0057ae;">:circle</span>, r<span style="color:#644a9b;">}</span> <span style="color:#ca60ca;">-></span> 0382 <span style="color:#aa5500;">IO</span><span style="color:#ca60ca;">.</span>puts<span style="color:#644a9b;">(</span><span style="color:#bf0303;">"Area = </span><span style="color:#006e28;">#{</span><span style="color:#b08000;">3.14</span> <span style="color:#ca60ca;">*</span> r <span style="color:#ca60ca;">*</span> r<span style="color:#006e28;">}</span><span style="color:#bf0303;">"</span><span style="color:#644a9b;">)</span> 0383 area_loop<span style="color:#644a9b;">()</span> 0384 <span style="font-weight:bold;">end</span> 0385 <span style="font-weight:bold;">end</span> 0386 <span style="font-weight:bold;">end</span> 0387 0388 <span style="color:#898887;"># Compile the module and create a process that evaluates `area_loop` in the shell</span> 0389 pid <span style="color:#ca60ca;">=</span> spawn<span style="color:#644a9b;">(</span><span style="font-weight:bold;">fn</span> <span style="color:#ca60ca;">-></span> <span style="color:#aa5500;">Geometry</span><span style="color:#ca60ca;">.</span>area_loop<span style="color:#644a9b;">()</span> <span style="font-weight:bold;">end</span><span style="color:#644a9b;">)</span> <span style="color:#898887;">#=> #PID<0.40.0></span> 0390 <span style="color:#898887;"># Alternatively</span> 0391 pid <span style="color:#ca60ca;">=</span> spawn<span style="color:#644a9b;">(</span><span style="color:#aa5500;">Geometry</span>, <span style="color:#0057ae;">:area_loop</span>, <span style="color:#006e28;">[]</span><span style="color:#644a9b;">)</span> 0392 0393 <span style="color:#898887;"># Send a message to `pid` that will match a pattern in the receive statement</span> 0394 send pid, <span style="color:#644a9b;">{</span><span style="color:#0057ae;">:rectangle</span>, <span style="color:#b08000;">2</span>, <span style="color:#b08000;">3</span><span style="color:#644a9b;">}</span> 0395 <span style="color:#898887;">#=> Area = 6</span> 0396 <span style="color:#898887;"># {:rectangle,2,3}</span> 0397 0398 send pid, <span style="color:#644a9b;">{</span><span style="color:#0057ae;">:circle</span>, <span style="color:#b08000;">2</span><span style="color:#644a9b;">}</span> 0399 <span style="color:#898887;">#=> Area = 12.56000000000000049738</span> 0400 <span style="color:#898887;"># {:circle,2}</span> 0401 0402 <span style="color:#898887;"># The shell is also a process, you can use `self` to get the current pid</span> 0403 self<span style="color:#644a9b;">()</span> <span style="color:#898887;">#=> #PID<0.27.0></span> 0404 0405 <span style="color:#898887;"># Code not found in the original, but needed to test the full range of the syntax</span> 0406 0407 <span style="font-weight:bold;">def</span> function, <span style="color:#0057ae;">do:</span> <span style="color:#644a9b;">{</span><span style="color:#0057ae;">:ok</span>, result<span style="color:#644a9b;">}</span> 0408 0409 <span style="color:#006e28;">[</span> 0410 <span style="color:#0057ae;">:a</span>, 0411 <span style="color:#0057ae;">:b</span>, 0412 <span style="color:#0057ae;">:c</span> 0413 <span style="color:#006e28;">]</span> 0414 0415 %<span style="color:#644a9b;">{</span> 0416 <span style="color:#0057ae;">a:</span> <span style="color:#bf0303;">"a"</span>, 0417 <span style="color:#0057ae;">b:</span> <span style="color:#bf0303;">"b"</span>, 0418 <span style="color:#0057ae;">c:</span> <span style="color:#bf0303;">"c"</span> 0419 <span style="color:#644a9b;">}</span> 0420 0421 %A<span style="color:#644a9b;">{</span> 0422 <span style="color:#0057ae;">a:</span> <span style="color:#bf0303;">"a"</span>, 0423 <span style="color:#0057ae;">b:</span> <span style="color:#bf0303;">"b"</span>, 0424 <span style="color:#0057ae;">c:</span> <span style="color:#bf0303;">"c"</span> 0425 <span style="color:#644a9b;">}</span> 0426 </pre></body></html>