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--- at:tutorial:basic [2007/03/31 12:43] – moved ambient
+++ at:tutorial:basic [2007/04/17 16:41] – * tvcutsem
@@ Line 1: / Line 1: @@
 <note>
-**IN PROGRESS**
+**This Tutorial is still under heavy construction!!**
-  - Could it be possible that the "table of contents" table in this page contains also a link to the actual page with the table of contents of the tutorial?
-  - (TOADD_1:) how to define and deal with multidimensional tables.
 </note>
+====== 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.
-==== Basic Programming ====
+===== Variables =====
-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 ====
-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 can contain any value.
-In the examples we use the interactive AmbientTalk shell (iat) where the input and output prompt are represented by > and >> , respectively.
+In the examples we use the interactive AmbientTalk shell (iat) where the input and output prompt are represented by > and <code>>></code> respectively.
 <code>
@@ Line 22: / Line 19: @@
 </code>
-Variable definitions can be combined with assignments as shown above. As in Pico, assignments uses the ":=" operator. Note that there must be an space between the variable and the ":=" operator in order for the parse to resolve the ambiguity between a keyword message and a assignment, e.g. "a := 1" is understood as an assignment while "a:" as a keyword. We will further elaborate on keywords in the following sections.
+Variable definitions can include an initialization expression that immediately initializes the variable. Variable assignment is performed by means of the well-known ":=" operator. AmbientTalk supports assignment to multiple variables as a single assignment expression. For this to work, the number of variable names on the left hand side of ":=" must match the number of expressions on the right hand side of ":=". A typical application of this is to swap the values of two variables more easily:
-An assignment consists of one or more expressions, providing that the number of expressions the the right hand side match the number of variables on the left hand side. This allows a permutation of variables such as:
 <code>
 >[x, y] := [ y, x ]
 >>[7,5]
 </code>
-Reference is just done by evaluating the variable.
-==== Tables ====
+As we will explain later, the ''[y,x]'' syntax simply denotes a literal table (a.k.a. an array).
+The variable name is used to refer a variable. The variable is evaluated when referenced.
+<code>
+>x
+>>7
+</code>
+<note>
+When using the '':='' assignment operator, beware of the following syntactic annoyance: the expression ''a := 1'' denotes an assignment to the variable ''a'', while ''a:= 1'' is misunderstood by the parser as ''a: = 1'', which is the invocation of a keyworded message named ''a:''. Keyworded message sends will be explained later on in this chapter. Hence, as a general rule, don't forget to always put a space between the variable name and the '':='' operator.
+</note>
+===== Tables =====
-As in Pico, indexed tables represent what other languages call arrays or lists. Tables indexes range from 1 to the size of the table. As variables, one can define, assign and refer to a table. Table definition is made also with the keyword def  in the following form:
+Indexed tables represent what other languages call arrays or lists. Tables are unidimensional and their indexes range from 1 to the size of the table. As variables, one can define, assign and refer to a table. Table definition is also made  with the keyword **def** in the following form:
 <code>
 def t[ <size> ] { <expression> }
@@ Line 41: / Line 48: @@
 >def z := 0
 >>0
->def t[5] { z := z + 1 }
+>def table[5] { z := z + 1 }
 >>[1, 2, 3, 4, 5]
 </code>
-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.
+<code>
+>def vowels := ["a", "e", "i", "o", "u"]
+>>["a", "e", "i", "o", "u"]
+>table[3] := vowels
+>>[1, 2, ["a", "e", "i", "o", "u"], 4, 5]
+>table[3][2]
+>>"e"
+</code>
+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.
+<code>
+>[ 1, table, "ambientTalk"]
+>>[1, [1, 2, ["a", "e", "i", "o", "u"], 4, 5], "ambientTalk"]
+</code>
+==== Table Splicing ====
+AmbientTalk provides the operator @ to splice tables into surrounding table expressions.
+<code>
+>[1,@[2,3],4]
+>>[1, 2, 3, 4]
+>[1, @[2,[3]], [4], @[5], @[], 6]
+>>[1, 2, [3], [4], 5, 6]
+</code>
+The splicing operator can be also used for matching table elements as shown below.
+<code>
+>def [first, @rest] := [1,2,3,4]
+>>[1, 2, 3, 4]
+>rest
+>>[2, 3, 4]
+</code>
+===== Functions =====
-As variables and tables, functions are defined with the keyworkd def in the form of:
+As variables and tables, functions are defined with the keyword **def** in the form of:
 <code>
 def functionname( <arglist> ) { <body> }
 </code>
-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:
+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:
 <code>
 >def square (x) { x*x }
@@ Line 59: / Line 100: @@
 >>25
 </code>
-As usual, functions can call themselves recusively. More interesting, you can also nest definitions of functions inside other functions as in:
+This example also illustrates how functions are called. Calls to functions without parameters must also include the parenthesis as shown below.
+<code>
+>def f(){nil}
+>><closure:f>
+>f()
+>>nil
+</code>
+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't do anything but returning the //nil// object.
+Functions have access to the enclosing environment of its definition as shown in the following example.
+<code>
+>def counter := 0
+>>0
+> def inc() { counter := counter + 1}
+>><closure:inc>
+>inc()
+>>1
+</code>
+Functions can call themselves recusively and they can also be nested in the definitions of other functions such as:
 <code>
 >def fac(n) {
@@ Line 67: / Line 127: @@
   inner(n,1)
 }
->>nil
+>><closure:fac>
 >fac(5)
 >>120
 </code>
-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't support function assigment. However, you can assign functions to variables. This means that a closure will be created and assigned to the variable. What follows is an example of such manipulation.
+This example also illustrates how a function can be made private by means of lexical scope. Variables and functions defined locally to functions are only visible in the scope of the function where there were defined. Note that local //inner// function is only visible inside the //fac// function and its nested scopes. Thus, calling //fac.inner(2,3)// will return a lookup failure error.
+==== Variable-Length Argument Functions ====
+You can create functions that take an arbitrary number of arguments by means of the splicing operator **@** which splices the table containing the parameters into the argument list.
 <code>
->def sum := 0
+>def sum(@args){ {
+  def total := 0;
+  foreach: { |el|  total := total + el } in: args;
+  total}
+>><closure:sum>
+>sum(1,2,3)
+>>6
+</code>
+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, we could define the //sum// function to take at least two numbers as shown below:
+<code>
+>def sum(a, b, @rest){ {
+  def total := a + b;
+  foreach: { |el|  total := total + el } in: rest;
+  total}
+>><closure:sum>
+>sum(1,2,3)
+>>6
+</code>
+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.
+<code>
+>def incr( number, step := 1){ number + step}
+>><closure:incr>
+>incr(3)
+>>4
+>incr(3,3)
+>>6
+</code>
+===== Closures =====
+As you have probably noticed in the previous examples,  the value returned by a function definition is a closure. Actually in AmbientTalk functions are implemented as named closures.
+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 //makeCell// function:
+<code>
+>def makeCell(val){
+   def getter() { val} ;
+   def setter(v) {val := v};
+  [getter, setter]
+}
+>><closure:makeCell>
+>def [get, set] := makeCell(42);
+>>[<closure:getter>, <closure:setter>]
+</code>
+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 //trustedFunction(get,set)// and  //distrustedFunction(get)//.
+===== Blocks =====
+In AmbientTalk, blocks are merely syntactic sugar for anonymous closures (aka lambdas).  Blocks are creating using the {} braces in the form of:
+<code>
+{ |<parlist>| <body> }
+</code>
+If the block do not require any parameter, the |<parlist>| can be omitted.  Consider a basic block to sum two numbers:
+<code>
+>{| a, b| a+ b} (3,2)
+>>5
+</code>
+Note that the argument list passed to the block can define the different types of arguments previously explained.
+<code>
+>{|a, b, @rest|
+   def total := a + b;
+   foreach: { |el| total := total + el} in: rest; total
+ }(1,2,3)
+>>6
+</code>
+This example also illustrates that blocks are also used to iterate over enumerations, such as in //foreach: {} in: table//.
+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:
+<code>
+>def square := { |x| x * x }
+>><closure:lambda>
+>square(3)
+>>9
+</code>
+===== 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:
+<code>
+def foo: arg1 bar: arg2 {...}
+def foo:bar:(arg1,arg2){..}
+</code>
+===== 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, the traditional operators +,-,*,/, >, <, <=, >=, =, !=  are nothing but syntactic sugar for method invocations. Therefore,  //1+1// is internally translated into //1.+(1)//. Unary operators are just applications, e.g. //-5// is internally translated into //-(5)//. What follows are some basic examples of manipulations with numeric types:
+<code>
+>1.inc()
+>>2
+>-1.abs()
+>>1
+>1.cos()
+>>0.5403023058681398
+>1 ** 5
+>>[1, 2, 3, 4]
+>5 *** 1
+>>[5, 4, 3, 2, 1]
+>1.4567.round()
+>>1
+>1.8.floor()
+>>1
+>1.4.ceiling()
+>>2
+</code>
+Numbers also support some useful iterator methods such as:
+<code>
+>6.to: 0 step: 2 do: { |i| system.println(i) }
+
+
+
+>>nil
+>3.doTimes: { |i| system.println(i) }
+
+
+
+>>nil
+</code>
+==== Texts ====
+A text data type represent a string of characters. Texts are often created using sequences of characters surrounded by double quotes ("). AmbientTalk doesn't use different notation for character or texts so a character can be created as //"a"//.  What follows is some basic examples of some useful native methods supported by text objects:
+<code>
+>"ambienttalk".explode()
+>>["a", "m", "b", "i", "e", "n", "t", "t", "a", "l", "k"]
+>"one, two, three".split(",")
+>>["one", "two", "three"]
+>"ambienttalk".replace: "[aeiou]" by: {
+ |vowel| vowel.toUpperCase()
+}
+>>"AmbIEnttAlk"
+>"A".toLowerCase()
+>>"a"
+>"ambienttalk".length()
+>>11
+</code>
+AmbientTalk also provides some useful support for pattern matching using regular expressions.
+<code>
+>"ambienttalk" ~= "java"
+>>false
+>"ambienttalk" ~= ".*tt.*"
+>>true
+</code>
+==== 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.
+<code>
+>[1,2,3].filter: {|e| e != 2 }
+>>[1, 3]
+>[1,2,3].map: { |i| i + 1 }
+>>[2, 3, 4]
+>def vowels := ["a", "e", "i", "o", "u"]
+>>["a", "e", "i", "o", "u"]
+>vowels.length
+>>5
+>vowels.at(1)
+>>"a"
+>vowels.atPut(1, "z")
+>>"z"
+>vowels
+>>["z", "e", "i", "o", "u"]
+>vowels.select(2,5).implode()
+>>"eio"
+>vowels.isEmpty()
+>>false
+</code>
+Tables also support some useful iterator methods as shown below.
+<code>
+>def sum:= 0;
 >>0
->sum := sum + 1
+>[1,2,3].each: { |i| sum := sum + i }
+>>nil
+>sum
+>>6
+>def sumNnum (@args) {
+  args.inject: 0 into: { |total, next| total + next}
+}
+>><closure:sumNnum>
+>sumNnum(1,2,3)
+>>6
+</code>
+==== Booleans ====
+AmbientTalk supports infix operators for booleans as &, | and !. As any native type, booleans are objects so, they respond to keyword messages such as:
+<code>
+<booleanexpr>.ifTrue: { ...}
+<booleanexpr>.ifFalse: { ...}
+<booleanexpr>.ifTrue: { ...}  ifFalse: {}
+<booleanexpr>.whileTrue: {...}
+</code>
+**=** 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:
+<code>
+>(0 < 1).ifTrue: { 0 }
+>>0
+>(3 != 5).ifTrue: { 1 } ifFalse: { 0 }
 >>1
->sum := { | x, y| x + y }
+> def [i, j] := [1,3]
+>>>[1, 3]
+>{i < j}.whileTrue: { system.println(i); i := i + 1 }
+
 >>nil
->sum(1,2)
->>3
 </code>
-==== 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:
+<code>
+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
+</code>
+An example of usage for some of these structures is shown below in the definition of the sort function.
+<code>
+>def sort(table, cmp := { |e1,e2| e1 < e2 }) {
+	def quickSort(table, low, high) {
+	   	def left := low;
+	   	def right := high;
+	   	def pivot := table[(left+right) /- 2];
+	   	def save := nil;
+        while: { left <= right } do: {
+		    while: { cmp(table[left], pivot) } do: {
+                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<right) then: { quickSort(table,low,right) };
+	   if: (high>left) then: { quickSort(table,left,high) };
+	   table;
+	  };
+	  quickSort(table, 1, table.getLength());
+	};
+>><closure:sort>
+>sort([2,37,6,4,5,8])
+>>[2, 4, 5, 6, 8, 37]
+</code>