Ambient-Oriented Programming

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at:tutorial:basic [2007/04/06 11:37] – * elisagat:tutorial:basic [2007/04/17 16:51] – tvcutsem
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 <note> <note>
-**This Tutorial is still under heavy construction**+**This Tutorial is still under heavy construction!!**
 </note> </note>
 ====== 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 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 ===== ===== 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 %%>>%% respectively. 
  
 <code> <code>
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 </code> </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 on the right hand side match the number of variables on the left hand side. This allows a permutation of variables such as: 
 <code> <code>
 >[x, y] := [ y, x ] >[x, y] := [ y, x ]
 >>[7,5] >>[7,5]
 </code> </code>
 +
 +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.  The variable name is used to refer a variable. The variable is evaluated when referenced. 
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 >>7 >>7
 </code> </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 ===== ===== Tables =====
  
-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:+The //table// is AmbientTalk's native compound data type. It is akin to what other languages call //arrays//. The main difference is that tables are indexed from ''1'' up to their ''length'', while arrays are indexed from ''0'' up to ''length-1''. Like with variables, one can define, assign and refer to a table. Table definitions are also formed with the keyword **def** in the following format:
 <code> <code>
-def t[ <size> ] { <expression> }+def t[ <sizeexpression> ] { <initexpression> }
 </code> </code>
-This means that the <expression> will be evaluated <size> times, i.e., one for each slot of the table. This allows expressions such as initializing a table of ascending numbers as shown below:+This constructs a table, the size of which is determined by ''<sizeexpression>''. The content of each slot is the result of evaluating ''<initexpression>''. This means that ''<initexpression>'' is evaluated for each slot in the table! Tables of e.g. ascending numbers are easily formed: 
 <code> <code>
 >def z := 0 >def z := 0
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 </code> </code>
  
-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.+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.
 <code> <code>
 >def vowels := ["a", "e", "i", "o", "u"] >def vowels := ["a", "e", "i", "o", "u"]
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 </code> </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.+As shown in the definition of the variable ''vowels'', AmbientTalk provides literal syntax to encode in-line tables. Table assignment and indexation work as usual, but recall that table indices range from ''1'' up to ''table.length''. Some more examples of literal tables:
  
 <code> <code>
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 ==== Table Splicing ==== ==== Table Splicing ====
  
-TODO!+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 ===== ===== Functions =====
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 >def square := { |x| x * x } >def square := { |x| x * x }
 >><closure:lambda> >><closure:lambda>
->square(1,2) +>square(3) 
->>3+>>9
 </code> </code>
  
at/tutorial/basic.txt · Last modified: 2020/02/09 22:05 by elisag