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- | < | ||
- | **This Tutorial is still under heavy construction!!** | ||
- | </ | ||
- | ====== Functional and Imperative Programming ====== | ||
- | |||
- | This part of the tutorial explains AmbientTalk as a simple expression language with a flexible syntax which resembles languages like Ruby, Python and Javascript. This section mainly describes the basic features of the language, namely variables, functions, tables (i.e. arrays) and control flow primitives. | ||
- | ===== Variables ===== | ||
- | |||
- | As usual, one can define, assign and refer to a variable. Variable definitions are made with the keyword **def**. Note that AmbientTalk is a dynamically typed language, so variables do not have a type but can contain any value. | ||
- | |||
- | In the examples we use the interactive AmbientTalk shell (iat) where the input and output prompt are represented by > and %%>> | ||
- | |||
- | < | ||
- | >def x := 5 | ||
- | >>5 | ||
- | >def y := x + 2 | ||
- | >>7 | ||
- | </ | ||
- | |||
- | Variable definitions can include an initialization expression that immediately initializes the variable. Variable assignment is performed by means of the well-known '': | ||
- | |||
- | < | ||
- | >[x, y] := [ y, x ] | ||
- | >> | ||
- | </ | ||
- | |||
- | As we will explain later, the '' | ||
- | |||
- | The variable name is used to refer a variable. The variable is evaluated when referenced. | ||
- | < | ||
- | >x | ||
- | >>7 | ||
- | </ | ||
- | |||
- | < | ||
- | When using the '': | ||
- | </ | ||
- | |||
- | ===== Tables ===== | ||
- | |||
- | The //table// is AmbientTalk' | ||
- | < | ||
- | def t[ < | ||
- | </ | ||
- | This constructs a table, the size of which is determined by ''< | ||
- | |||
- | < | ||
- | >def z := 0 | ||
- | >>0 | ||
- | >def table[5] { z := z + 1 } | ||
- | >>[1, 2, 3, 4, 5] | ||
- | </ | ||
- | |||
- | Although there is no special constructor for definition of multidimensional tables, a table entry can contain another table. This is internally stored as a one-dimensional table whose entries are other tables. | ||
- | < | ||
- | >def vowels := [" | ||
- | >> | ||
- | > | ||
- | >>[1, 2, [" | ||
- | > | ||
- | >>" | ||
- | </ | ||
- | |||
- | As shown in the definition of the variable '' | ||
- | |||
- | < | ||
- | >[ 1, table, " | ||
- | >>[1, [1, 2, [" | ||
- | </ | ||
- | |||
- | ==== Table Splicing ==== | ||
- | |||
- | AmbientTalk provides the //splice operator// '' | ||
- | < | ||
- | > | ||
- | >>[1, 2, 3, 4] | ||
- | >[1, @[2,[3]], [4], @[5], @[], 6] | ||
- | >>[1, 2, [3], [4], 5, 6] | ||
- | </ | ||
- | |||
- | The splicing operator can be also used in the left-hand side of an assignment or definition to separate the head of a table with its rest elements, as shown below. | ||
- | < | ||
- | >def [first, @rest] := [1,2,3,4] | ||
- | >>[1, 2, 3, 4] | ||
- | >rest | ||
- | >>[2, 3, 4] | ||
- | </ | ||
- | |||
- | ===== Functions ===== | ||
- | |||
- | Analogous to variables and tables, functions are defined with the keyword **def** in the form of: | ||
- | < | ||
- | def functionname( < | ||
- | </ | ||
- | The argument list is just a list of local variables which are always evaluated one by one from left to right. Hence, AmbientTalk employs // | ||
- | < | ||
- | >def square (x) { x*x } | ||
- | >>nil | ||
- | > | ||
- | >>25 | ||
- | </ | ||
- | This example also illustrates the // | ||
- | < | ||
- | >def f() { nil } | ||
- | >>< | ||
- | >f() | ||
- | >>nil | ||
- | </ | ||
- | The return value of a function is the result of the last executed statement. Functions always return a value, but a function can always opt to return the //nil// object. | ||
- | |||
- | < | ||
- | A function definition is a statement. The body of a function can contain a list of statements, each separated by '';'' | ||
- | < | ||
- | def funA() { | ||
- | // do something useful | ||
- | } | ||
- | def funB() { | ||
- | // do something else | ||
- | } | ||
- | </ | ||
- | The parser will complain saying that '' | ||
- | </ | ||
- | |||
- | Functions in AmbientTalk are //lexically scoped//, which means that free variables are looked up in the enclosing environment of the function definition. This is illustrated in the following example: | ||
- | < | ||
- | >def counter := 0 | ||
- | >>0 | ||
- | > def inc() { counter := counter + 1} | ||
- | >>< | ||
- | >inc() | ||
- | >>1 | ||
- | </ | ||
- | |||
- | Functions can call themselves recusively and they can also be nested in the definitions of other functions such as: | ||
- | < | ||
- | >def fac(n) { | ||
- | def inner(n, result) { | ||
- | if: (n = 0) then: { result } else: { inner( n-1, n * result) | ||
- | }; | ||
- | inner(n,1) | ||
- | } | ||
- | >>< | ||
- | >fac(5) | ||
- | >>120 | ||
- | </ | ||
- | |||
- | This example also illustrates how a function can be made " | ||
- | |||
- | ==== Variable-Length Argument Functions ==== | ||
- | |||
- | You can create functions that take an arbitrary number of arguments (also known as a variable arity or polyadic function) by means of the splicing operator '' | ||
- | < | ||
- | >def sum(@args) { | ||
- | def total := 0; | ||
- | foreach: { |el| total := total + el } in: args; | ||
- | total | ||
- | }; | ||
- | >>< | ||
- | > | ||
- | >>6 | ||
- | </ | ||
- | |||
- | When the //sum// function is called, the //args// table is spliced and passed as the argument list to the function. Note that the //args// table can also be modified inside the body of the function. | ||
- | |||
- | Alternatively, | ||
- | < | ||
- | >def sum(a, b, @rest){ { | ||
- | def total := a + b; | ||
- | foreach: { |el| total := total + el } in: rest; | ||
- | total} | ||
- | >>< | ||
- | > | ||
- | >>6 | ||
- | </ | ||
- | |||
- | In that case, the //sum// function still accepts an arbitrary number of arguments as long as two arguments are supplied. //a// and //b// are considered as mandatory arguments of the argument list. | ||
- | |||
- | A function can also declare optional arguments as shown below. Optional arguments can be omitted in a function call. Internally, the default value provided in their definition is passed as the argument to the function. | ||
- | < | ||
- | >def incr( number, step := 1){ number + step} | ||
- | >>< | ||
- | >incr(3) | ||
- | >>4 | ||
- | > | ||
- | >>6 | ||
- | </ | ||
- | |||
- | ===== Closures ===== | ||
- | |||
- | As you have probably noticed in the previous examples, | ||
- | |||
- | The function name can be thus used to refer the function (without calling it). This will also return a closure to that function. As an example consider the // | ||
- | < | ||
- | >def makeCell(val){ | ||
- | def getter() { val} ; | ||
- | def setter(v) {val := v}; | ||
- | [getter, setter] | ||
- | } | ||
- | >>< | ||
- | >def [get, set] := makeCell(42); | ||
- | >> | ||
- | </ | ||
- | |||
- | This example also illustrates how a function can make public some of its local fields or functions by returning them as its return value. The get and set could be then passed as arguments to other functions such as // | ||
- | |||
- | ===== Blocks ===== | ||
- | |||
- | In AmbientTalk, | ||
- | < | ||
- | { |< | ||
- | </ | ||
- | If the block do not require any parameter, the |< | ||
- | < | ||
- | >{| a, b| a+ b} (3,2) | ||
- | >>5 | ||
- | </ | ||
- | Note that the argument list passed to the block can define the different types of arguments previously explained. | ||
- | < | ||
- | >{|a, b, @rest| | ||
- | def total := a + b; | ||
- | | ||
- | | ||
- | >>6 | ||
- | </ | ||
- | |||
- | This example also illustrates that blocks are also used to iterate over enumerations, | ||
- | |||
- | AmbientTalk doesn’t support function assigment. However, one can assign blocks to variables. In order to call the block the name of the variable must be used. If the block defined parameters, these are required to the call as argument list. What follows is an example of such manipulation: | ||
- | < | ||
- | >def square := { |x| x * x } | ||
- | >>< | ||
- | > | ||
- | >>9 | ||
- | </ | ||
- | |||
- | ===== Keywords ===== | ||
- | |||
- | AmbientTalk supports keyword messages. We have already seen some examples of keyword messages in the previous sections such as the foreach structure. In AmbientTalk keywords are transformed by the parser into functions in the form: | ||
- | < | ||
- | def foo: arg1 bar: arg2 {...} | ||
- | def foo: | ||
- | </ | ||
- | |||
- | ===== Native Data Types ===== | ||
- | |||
- | |||
- | The basic types in AmbientTalk are numbers, fractions, text, tables and booleans. In fact, these data types are nothing but objects and as such, they respond to a variety of native methods. Objects will be the subject of the next chapter of the tutorial. This section explains the basic data types and includes some examples how to manipulate them. The complete list of methods can be found in the language reference. | ||
- | |||
- | ==== Numerical data types ==== | ||
- | |||
- | AmbientTalk supports numbers and fractions which represent what other languages call integers and floating point numbers, respectively. | ||
- | |||
- | Note that since numerical types are objects in AmbientTalk, | ||
- | < | ||
- | >1.inc() | ||
- | >>2 | ||
- | > | ||
- | >>1 | ||
- | >1.cos() | ||
- | >> | ||
- | >1 ** 5 | ||
- | >>[1, 2, 3, 4] | ||
- | >5 *** 1 | ||
- | >>[5, 4, 3, 2, 1] | ||
- | > | ||
- | >>1 | ||
- | > | ||
- | >>1 | ||
- | > | ||
- | >>2 | ||
- | </ | ||
- | |||
- | Numbers also support some useful iterator methods such as: | ||
- | < | ||
- | >6.to: 0 step: 2 do: { |i| system.println(i) } | ||
- | 6 | ||
- | 4 | ||
- | 2 | ||
- | >> | ||
- | > | ||
- | 1 | ||
- | 2 | ||
- | 3 | ||
- | >>nil | ||
- | </ | ||
- | |||
- | ==== Texts ==== | ||
- | |||
- | |||
- | A text data type represent a string of characters. Texts are often created using sequences of characters surrounded by double quotes ("). AmbientTalk doesn' | ||
- | < | ||
- | >" | ||
- | >> | ||
- | >" | ||
- | >> | ||
- | >" | ||
- | | ||
- | } | ||
- | >>" | ||
- | >" | ||
- | >>" | ||
- | >" | ||
- | >>11 | ||
- | </ | ||
- | |||
- | AmbientTalk also provides some useful support for pattern matching using regular expressions. | ||
- | < | ||
- | >" | ||
- | >> | ||
- | >" | ||
- | >> | ||
- | </ | ||
- | |||
- | ==== Tables ==== | ||
- | |||
- | |||
- | We have already introduce how to define tables. Let us now focus on how to manipulate them with the native methods provided by the table object. | ||
- | < | ||
- | > | ||
- | >>[1, 3] | ||
- | > | ||
- | >>[2, 3, 4] | ||
- | >def vowels := [" | ||
- | >> | ||
- | > | ||
- | >>5 | ||
- | > | ||
- | >>" | ||
- | > | ||
- | >>" | ||
- | >vowels | ||
- | >> | ||
- | > | ||
- | >>" | ||
- | > | ||
- | >> | ||
- | </ | ||
- | |||
- | Tables also support some useful iterator methods as shown below. | ||
- | |||
- | < | ||
- | >def sum:= 0; | ||
- | >>0 | ||
- | > | ||
- | >>nil | ||
- | >sum | ||
- | >>6 | ||
- | >def sumNnum (@args) { | ||
- | args.inject: | ||
- | } | ||
- | >>< | ||
- | > | ||
- | >>6 | ||
- | </ | ||
- | |||
- | ==== Booleans ==== | ||
- | |||
- | |||
- | AmbientTalk supports infix operators for booleans as &, | and !. As any native type, booleans are objects so, they respond to keyword messages such as: | ||
- | < | ||
- | < | ||
- | < | ||
- | < | ||
- | < | ||
- | </ | ||
- | |||
- | **=** and **!=** are the infix operators for equality and inequality. **true** and **false** are the boolean constant objects. What follows is some basic examples of boolean manipulation: | ||
- | < | ||
- | >(0 < 1).ifTrue: { 0 } | ||
- | >>0 | ||
- | >(3 != 5).ifTrue: { 1 } ifFalse: { 0 } | ||
- | >>1 | ||
- | > def [i, j] := [1,3] | ||
- | >>> | ||
- | >{i < j}.whileTrue: | ||
- | 1 | ||
- | 2 | ||
- | >>nil | ||
- | </ | ||
- | |||
- | Boolean infix operators such as & and | are not shortcut. Thus, both arguments will be evaluated. For lazy evaluation, you should use the natives methods. For example, false.and: { 1/0 } will return false without executing the second argument. | ||
- | |||
- | ===== Control Flow Structures ===== | ||
- | |||
- | Control flow structures are defined in the lexical root of AmbientTalk. The lexical root is an object containing globally visible native methods. We have already seen in the previous sections examples of usage of the foreach and if/then structures. The complete list of traditional control flow structures defined in AmbientTalk is shown below: | ||
- | < | ||
- | if: booleanCondition then: { consequent } | ||
- | if: booleanCondition then: { consequent } else: { alternative } | ||
- | while: { condition } do: { body } | ||
- | foreach: { |v| body } in: [ table ] | ||
- | do: { body } if: condition | ||
- | do: { body } unless: condition | ||
- | </ | ||
- | An example of usage for some of these structures is shown below in the definition of the sort function. | ||
- | < | ||
- | >def sort(table, cmp := { |e1,e2| e1 < e2 }) { | ||
- | def quickSort(table, | ||
- | def left := low; | ||
- | def right := high; | ||
- | def pivot := table[(left+right) /- 2]; | ||
- | def save := nil; | ||
- | while: { left <= right } do: { | ||
- | while: { cmp(table[left], | ||
- | left := left + 1 | ||
- | }; | ||
- | while: { cmp(pivot, table[right]) } do: { | ||
- | right := right - 1 | ||
- | }; | ||
- | if: (left <= right) then: { | ||
- | // swap elements | ||
- | save := table[left]; | ||
- | table[left] := table[right]; | ||
- | table[right] := save; | ||
- | left := left + 1; | ||
- | right := right - 1; | ||
- | }; | ||
- | }; | ||
- | if: (low< | ||
- | if: (high> | ||
- | | ||
- | }; | ||
- | quickSort(table, | ||
- | }; | ||
- | >>< | ||
- | > | ||
- | >>[2, 4, 5, 6, 8, 37] | ||
- | </ |