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--- at:tutorial:basic [2007/04/17 16:24] – * tvcutsem
+++ at:tutorial:basic [2007/04/17 16:40] – tvcutsem
@@ Line 4: / Line 4: @@
 ====== 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 =====
-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 19: / 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 on 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>
+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.
@@ Line 32: / Line 33: @@
 >>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 =====