- All variable names must start with an uppercase letter.────所有的变量必须用大写字母开头
- 例子：
Eshell V5.5.5 (abort with ^G)
1> X = 123456789.
123456789
2> X.
123456789
3> X*X*X*X*X*X*X
3> .
437124189620885610010004822109262358637075660656881926429 - Single Assignment Is Like Algebra，Variables That Don’t Vary────赋值就像代数里一样，不变的变量。(回想一下，在没有接触C等其他高级语言之前，代数中的变量是怎么样的。没错，它们的值是不变的)。 例子(接上例):
4> X = 1234.
=ERROR REPORT==== 16-Jul-2008::22:34:38 ===
Error in process <0.31.0> with exit value: {{badmatch,1234},[{erl_eval,expr,3}]}
** exited: {{badmatch,1234},[{erl_eval,expr,3}]} ** - Pattern Matching────模式匹配。在其他语言(C，JAVA，RUBY and so on)中，“=”都是赋值用，而在Erlang中它是作为模式匹配用的。比如：Lhs = Rhs，它的意思是，计算右边的值(Rhs)，然后和左边的(Lhs)匹配。 例子：
Eshell V5.5.5 (abort with ^G)
1> X = (2+4).
6
2> Y = 10.
10
3> X = 6.
6
4> X = Y.
=ERROR REPORT==== 16-Jul-2008::22:41:58 ===
Error in process <0.31.0> with exit value: {{badmatch,10},[{erl_eval,expr,3}]}
** exited: {{badmatch,10},[{erl_eval,expr,3}]} **
Floating-Point Numbers(浮点数)
- “/” always returns a float; thus, 4/2 evaluates to 2.0000 (in the shell). ────“/”操作符总是返回一个浮点数;所以，4/2计算得2.0000(in the shell)。
- N div M and N rem M are used for integer division and remainder; thus, 5 div 3 is 1, and 5 rem 3 is 2.────N div M 和 N rem M 用于整除和计算余数，因而，5 div 3 等于1,而5 rem 3 等于2.
- 例子：
Eshell V5.5.5 (abort with ^G)
1> 5/3.
1.66667
2> 4/2.
2.00000
3> 5 div 3.
1
4> 5 rem 3.
2
5> 4 div 2.
2
6> Pi = 3.14159.
3.14159
7> R = 5.
5
8> Pi * R * R.
78.5397
Atoms
- In Erlang, atoms are used to represent different non-numerical constant values.────在Erlang中，atoms被用来代表不同的非数字常量。
- In Erlang, atoms are global, and this is achieved without the use of macro definitions or include files.────在Erlang中，atoms是全局的，而且这不是通过宏定义或者包含头文件来实现的。
- Atoms start with lowercase letters, followed by a sequence of alphanumeric characters or the underscore (_) or at (@) sign.7 For example: red, december, cat, meters, yards, joe@somehost, and a_long_name.────Atoms以小写字母开头，跟一串字母数字或者下划线(_)或者at(@)标志。比如：red, december, cat, meters, yards, joe@somehost, a_long_name。
- The value of an atom is just the atom.────一个atom的值就是atom本身。例子：
1> hello.
hello
Tuples(元组)
- You can create a tuple by enclosing the values you want to represent in curly brackets and separating them with commas. for example:{joe, 1.82}────你可能用大括号括起用逗号分隔的值来创建一个元组。比如{joe, 1.82}
- Tuples are similar to structs in C────元组和C语言中的结构类似。
- To make it easier to remember what a tuple is being used for, it’s common to use an atom as the first element of the tuple, which describes what the tuple represents.────为了能更加容易的记住一个元组是做什么用的，通常用一个atom来做元组的第一个元素，用来描述这个元组代表什么。
- Tuples can be nested.────元组可以嵌套。例子：
Eshell V5.5.5 (abort with ^G)
1> Person = {person,
1> {name, joe},
1> {height, 1.82},
1> {footsize, 42},
1> {eyecolor, brown}}.
{person,{name,joe},{height,1.82000},{footsize,42},{eyecolor,brown}} 2> F = {firstName, joe}.
{firstName,joe}
3> L = {lastName, armstrong}.
{lastName,armstrong}
4> P = {person, F, L}.
{person,{firstName,joe},{lastName,armstrong}}- Extracting Values from Tuples────从元组中抽取数据
- pattern matching is fundamental to Erlang and that it’s used for lots of different tasks.────模式匹配是Erlang的基础而且它被用于许多不同的任务。
- If we want to extract some values from a tuple, we use the pattern
matching operator =.────如果我们想要从一个元组中抽取数据，我们用匹配操作符“=”。 - 例子：
Eshell V5.5.5 (abort with ^G)
1> Point = {point, 10, 45}.
{point,10,45}
2> {point, X, Y} = Point
2> .
{point,10,45}
3> X.
10
4> Y.
45 - 一个更为复杂的例子：
Eshell V5.5.5 (abort with ^G)
1> Person={person, {name, {first, joe}, {last, armstrong}}, {footsize, 42}}.
{person,{name,{first,joe},{last,armstrong}},{footsize,42}}
2> {_,{_,{_,Who},_},_} = Person.
{person,{name,{first,joe},{last,armstrong}},{footsize,42}}
3> Who.
joe - _ as a placeholder for variables that we’re not interested in. The symbol _ is called an anonymous variable.────"_"作为占位符。符号"_"叫作匿名变量。
Lists(列表)
- create a list：
Eshell V5.5.5 (abort with ^G)
1> ThingsToBuy = [{apples, 10}, {pears, 6}, {milk, 3}].
[{apples,10},{pears,6},{milk,3}]
2> [1+7, hello, 2-2, {cost, apple, 30-20}, 3].
[8,hello,0,{cost,apple,10},3] - We call the first element of a list the head of the list.what’s left is called the tail of the list.────我们把列表的第一个元素叫做“头”，剩下的叫做“尾”。比如[1,2,3,4,5]这个列表中，头是整数1,尾是列表[2,3,4,5]。
- Note that the head of a list can be anything, but the tail of a list is usually also a list.────注意，一个列表的头可以是任何类型，但是尾通常也是一个列表。
- (*)If T is a list, then [H|T] is also a list, with head H and tail T.Whenever we construct a list using a [...|T] constructor, we should make sure that T is a list.────如果T是一个列表，那么[H|T]也是一个列表，头是H，尾是T。不管我们如何用[...|T]来构造一个列表，必须要保证T一定是一个列表。
- 3>
ThingsToBuy1 = [{oranges, 4}, {newspaper, 1}|ThingsToBuy].
[{oranges,4},{newspaper,1},{apples,10},{pears,6},{milk,3}]
(接上面的例子) - Extracting Elements from a List────从列表中提取元素
4>[Buy1|ThingsToBuy2] = ThingsToBuy1.(接上面例子)
[{oranges,4},{newspaper,1},{apples,10},{pears,6},{milk,3}]
5> Buy1.
{oranges,4}
6> [Buy2, Buy3|ThingsToBuy3] = ThingsToBuy2.
[{newspaper,1},{apples,10},{pears,6},{milk,3}]
7> Buy2.
{newspaper,1}
8> Buy3.
{apples,10}
9> ThingsToBuy3.
[{pears,6},{milk,3}]
Strings(字符串)
- Strictly speaking, there are no strings in Erlang. Strings are really just lists of integers. Strings are enclosed in double quotation marks (")────严格的讲，Erlang中并没有字符串。所谓字符串实际上只是整数的列表。字符串是用双引号括起来的。
Eshell V5.5.5 (abort with ^G)
1> Name = "Hello".
"Hello"- When the shell prints the value of a list it prints the list as a string, but only if all the integers in the list represent printable characters.────当shell打印一列表的值的时候，如果这个列表中的整数都能代表一个可打印的字符，它就会把这个列表当作一个字符串来打印。
2> [1,2,3].
[1,2,3]
3> [83,117,114,112,114,105,115,101].
"Surprise"
4> [1,83,117,114,112,114,105,115,101].
[1,83,117,114,112,114,105,115,101]- We don’t need to know which integer represents a particular character.We can use the “dollar syntax” for this purpose.────我们没有必要去知道哪个整数代表哪个字符，我们可以用美元符号"$"来做这件事情。(见下例)
5> I = $s.
115
6> [I-32, $u, $r, $p, $r, $i, $s, $e].
"Surprise"
- Note: The command f() tells the shell to forget any bindings it has. After this command, all variables become unbound────注意：f()命令会告诉shell忘记掉所以的绑定。在这个命令之后，所以的变量都是未绑定的。
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