at:tutorial:basic
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at:tutorial:basic [2007/04/04 09:17] – * elisag | at:tutorial:basic [2007/04/06 15:18] – * elisag | ||
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< | < | ||
- | **IN PROGRESS** | + | **This Tutorial is still under heavy construction!!** |
- | - Could it be possible that the "table of contents" | + | |
- | - (TOADD_1:) how to define and deal with multidimensional tables. | + | |
</ | </ | ||
- | + | ====== Functional and Imperative Programming | |
- | ==== Functional and Imperative Programming ==== | + | |
This part of the tutorial shows AmbientTalk as a simple expression language with a minimum syntax which resembles very on Java script. This section mainly describes the basic features of the language, namely variables, functions and tables and control flow. | This part of the tutorial shows AmbientTalk as a simple expression language with a minimum syntax which resembles very on Java script. This section mainly describes the basic features of the language, namely variables, functions and tables and control flow. | ||
- | ==== Variables ==== | + | ===== 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, they just contain values. | 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, they just contain values. | ||
Line 29: | Line 26: | ||
>> | >> | ||
</ | </ | ||
- | Reference is just done by evaluating the variable. | ||
- | ==== Tables ==== | + | The variable name is used to refer a variable. The variable is evaluated when referenced. |
+ | < | ||
+ | >x | ||
+ | >>7 | ||
+ | </ | ||
+ | |||
+ | ===== Tables | ||
- | As in Pico, indexed | + | Indexed |
< | < | ||
def t[ < | def t[ < | ||
Line 41: | Line 43: | ||
>def z := 0 | >def z := 0 | ||
>>0 | >>0 | ||
- | > | + | > |
>>[1, 2, 3, 4, 5] | >>[1, 2, 3, 4, 5] | ||
</ | </ | ||
- | Table entries can also contain another tables. -> TOADD_1 | ||
- | ==== Functions ==== | + | Although there is no special constructor for definition of multidimensional tables, a table entry can contain another table. This is internally stored as a unidimensional table whose entries are other tables. |
+ | < | ||
+ | >def vowels := [" | ||
+ | >> | ||
+ | > | ||
+ | >>[1, 2, [" | ||
+ | > | ||
+ | >>" | ||
+ | </ | ||
+ | |||
+ | As shown in the definition of the varible //vowels//, evaluating a series of comma-separated data types between square brackets (aka a tabulation) results in a table. | ||
+ | |||
+ | < | ||
+ | >[ 1, table, " | ||
+ | >>[1, [1, 2, [" | ||
+ | </ | ||
+ | |||
+ | ==== Table Splicing ==== | ||
+ | |||
+ | AmbientTalk provides an operator (@) to splice tables into surrounding table expressions. | ||
+ | < | ||
+ | > | ||
+ | >>[1, 2, 3, 4] | ||
+ | >[1, @[2,[3]], [4], @[5], @[], 6] | ||
+ | >>[1, 2, [3], [4], 5, 6] | ||
+ | </ | ||
+ | |||
+ | The splicing operator can be also used for matching table elements as shown below. | ||
+ | < | ||
+ | >def [first, @rest] := [1,2,3,4] | ||
+ | >>[1, 2, 3, 4] | ||
+ | >rest | ||
+ | >>[2, 3, 4] | ||
+ | </ | ||
+ | |||
+ | ===== Functions | ||
- | As variables and tables, functions are defined with the keyworkd | + | As variables and tables, functions are defined with the keyword **def** in the form of: |
< | < | ||
def functionname( < | def functionname( < | ||
</ | </ | ||
- | The argument list is just a list of local variables which are always evaluated one by one from left to right. | + | The argument list is just a list of local variables which are always evaluated one by one from left to right. A basic function looks like this: |
< | < | ||
>def square (x) { x*x } | >def square (x) { x*x } | ||
Line 59: | Line 95: | ||
>>25 | >>25 | ||
</ | </ | ||
- | As usual, | + | This example also illustrates how functions |
+ | < | ||
+ | >def f(){nil} | ||
+ | >>< | ||
+ | >f() | ||
+ | >> | ||
+ | </ | ||
+ | The return value of a function is the result of the last statement executed. Functions must always return a value - i.e. they cannot be abstract. The example also illustrates how to create dumb function that doesn' | ||
+ | |||
+ | Functions have access to the enclosing environment of its definition as shown in the following example. | ||
+ | < | ||
+ | >def counter := 0 | ||
+ | >>0 | ||
+ | > def inc() { counter := counter + 1} | ||
+ | >>< | ||
+ | >inc() | ||
+ | >>1 | ||
+ | </ | ||
+ | |||
+ | Functions | ||
< | < | ||
>def fac(n) { | >def fac(n) { | ||
Line 67: | Line 122: | ||
inner(n,1) | inner(n,1) | ||
} | } | ||
- | >>nil | + | >>< |
>fac(5) | >fac(5) | ||
>>120 | >>120 | ||
</ | </ | ||
- | Note that variables and functions defined locally to functions are only visible in the scope of the function where there were defined. Notice also that a function name can also be used just to refer the function but without calling it. | ||
- | Unlike Pico, AmbientTalk doesn' | + | This example also illustrates how a function can be made private by means of lexical scope. Variables |
+ | |||
+ | ==== Variable-Length Argument Functions ==== | ||
+ | |||
+ | You can create functions that take an arbitrary number | ||
< | < | ||
- | >def sum := 0 | + | >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} | ||
+ | >>< | ||
+ | > | ||
+ | >>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 } | ||
+ | >>< | ||
+ | > | ||
+ | >>3 | ||
+ | </ | ||
+ | |||
+ | ===== 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, | ||
+ | < | ||
+ | > | ||
+ | >>2 | ||
+ | > | ||
+ | >>1 | ||
+ | > | ||
+ | >> | ||
+ | >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 | ||
+ | >>nil | ||
+ | > | ||
+ | 1 | ||
+ | 2 | ||
+ | 3 | ||
+ | >> | ||
+ | </ | ||
+ | |||
+ | ==== Texts ==== | ||
+ | |||
+ | |||
+ | A text data type represent a string of characters. Texts are often created using sequences of characters surrounded by double quotes ("). AmbientTalk doesn' | ||
+ | < | ||
+ | >" | ||
+ | >> | ||
+ | >" | ||
+ | >> | ||
+ | >" | ||
+ | | ||
+ | } | ||
+ | >>" | ||
+ | >" | ||
+ | >>" | ||
+ | >" | ||
+ | >> | ||
+ | </ | ||
+ | |||
+ | 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 | ||
+ | > | ||
+ | >>" | ||
+ | > | ||
+ | >>" | ||
+ | > | ||
+ | >> | ||
+ | > | ||
+ | >>" | ||
+ | > | ||
+ | >> | ||
+ | </ | ||
+ | |||
+ | Tables also support some useful iterator methods as shown below. | ||
+ | |||
+ | < | ||
+ | >def sum:= 0; | ||
>>0 | >>0 | ||
- | >sum := sum + 1 | + | >[1, |
+ | >> | ||
+ | >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 | >>1 | ||
- | >sum := { | x, y| x + y } | + | > def [i, j] := [1,3] |
+ | >>> | ||
+ | >{i < j}.whileTrue: | ||
+ | 1 | ||
+ | 2 | ||
>>nil | >>nil | ||
- | > | ||
- | >>3 | ||
</ | </ | ||
- | ==== Blocks | + | 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] | ||
+ | </ |
at/tutorial/basic.txt · Last modified: 2020/02/09 22:05 by elisag