Chapter 2 The DynaScript Language
Expressions are combinations of variables, literal values, operators, and other expressions. The right side of an assignment statement is an expression.
The following statements illustrate various kinds of expressions:
surfaceArea = (2 * 3.14159 * radius * height ) ;
surfaceArea = surfaceArea + ( 2 * 3.14159 * radius * radius ) ;
quote = "Full fathom five" + " thy father lies" ;
address = 10 + " Downing Street" ;
Name = "Moonunit " + 2 ;
Every expression has a value and a datatype.
The datatype is one of numeric
, string
, Boolean
, function
, object
,
or null
.
In some cases, the value of an expression is
obvious; in others, it is not. For example, (2 * 3)
is
clearly a numeric expression with value 6
,
and "To be or not to be"
is
a character string. However, it is not quite so obvious what the
result of adding a number and a string is, as in the expression 10 + " Downing
Street"
.
To make meaningful evaluation of expressions
possible, DynaScript has rules for automatic conversion of datatypes.
In the above example, 10
is
converted to a string and concatenated with the other string to
give the final value.
An operator can act on expressions of certain datatypes. For example, the multiplication operator (*) can act on numeric expressions, but cannot act on string expressions:
// valid use of multiplication
( 2 * 3.14159 * radius )
// invalid use of multiplication
"What" * "happens now?"
Some operators can act on more than one datatype. The most common of these is the addition operator (+). The addition operator can add two numbers together, or concatenate two strings.
Operators are either ternary, binary, or unary. Binary operators act on two operands, such as the arithmetic operators:
x + y
45 / 56
Unary operators act on only one expression.
For example, the postfix ++
operator
adds one to the value of a variable:
x++ ;
The less common ternary operators act on three expressions.
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