GPDL Expressions
Like most other languages, GPDL allows you to manipulate data using expressions such as:
HeightInInches = 12 * HeightInFeet;
But since everything in GPDL is a string rather than a number, you will have to get used to some strange-looking expressions when you wish to manipulate numbers. The way to write the above example in GPDL would be
HeightInInches = $TIMES(12, HeightInFeet);
This expression is equivalent:
HeightInInches = $TIMES("12", HeightInFeet);
because GPDL will automatically convert '12' to a string ("12"). The reason that the expression
HeightInInches = 12 * HeightInFeet;
will not work is because there is no binary operator '*' for text strings. The text might represent numbers, as in
HeightInInches = 12 * 6; // assuming HeightInFeet = "6"
but it could also just as easily not, as in
HeightInInches = 12 * "I'm six feet tall";
The $TIMES operator tells the compiler that you want to convert the two text parameters into numbers and perform multiplication on them.
There is an operator for combining strings:
+ |
Concatenates two strings |
Second, there are operators comparing strings. All of these compare the strings as alphanumeric text. For example, "Dog" is greater than "Cat" because 'D' comes after 'C' in the alphabet. Lower-case letters come after the upper-case letters. "cat" is greater than "Dog". All these operators have as their result either true (represented by "1") or false (represented by "").
> |
Greater |
< |
Less |
== |
Equal |
>= |
Greater than or equal |
<= |
Less than or equal |
!= |
Not equal |
&& |
Both are non-empty |
|| |
At least one is non empty |
|
|
Third, there are operators for manipulating numbers as 32-bit integers. Each of these converts its arguments to 32-bit numbers, performs the appropriate function, and then converts the result to a string. SeeData Type Conversions
+# |
Addition |
-# |
Subtraction |
*# |
Multiplication |
/# |
Division |
%# |
Remainder |
&# |
Bitwise AND |
|# |
Bitwise OR |
^# |
Bitwise Exclusive OR |
Fourth, there are operators to compare 32-bit numbers.
==# |
Equal |
!=# |
Not equal |
<# |
Less than |
<=# |
Less than or equal |
># |
Greater than |
>=# |
Greater than or equal |
Fifth, there are functions to operate on strings as decimal digits with infinite precision. They are not fast. But you can easily compute 1000-digit numbers if you so please.
$EQUAL |
$LESS |
$GREATER |
$PLUS |
$MINUS |
$TIMES |
$DIV |
$MOD |
$NOT |
All of the operators have a precedence. For example, multiplications take place before additions. The normal precedence can be overridden with the use of parentheses. For example:
x = 12 /# ( Y +# Z )
means that 12 will be divided by the sum of Y and Z.
Here is the normal precedence of the operators:
Logical OR |
|| |
Logical AND |
&& |
Bitwise OR |
|# |
Bitwise XOR |
^# |
Bitwise AND |
&# |
Equality |
== and ==# and != and !=# |
Comparison |
< and <# and > etc |
plus/minus |
+ and +# and -# |
multiply/divide |
*# and /# and %# |
In all cases, the operators and functions that have a true/false value as their result return a string with the single digit '1' to represent a true result and an empty string as false.
Some more examples to illustrate how numbers and strings are manipulated:
$RETURN "10" + "5"; // returns "105"
$RETURN 10 + 5; // returns "105"
$RETURN 10 +# 5; // returns "15", the '+#' means treat both params as numbers
$RETURN "10" + "-5"; // returns "10-5"
$RETURN 10 + -5; // error, there is no unary operator '-' for strings
$RETURN 10 - 5; // error, there is no binary operator '-' for strings
$RETURN 10 -# 5; // returns "5"
$RETURN $PLUS(10, 5); // returns "15"
$RETURN $PLUS("10", "5"); // returns "15"
$RETURN $MINUS(10, 5); // returns "5"
$RETURN $PLUS("10", "-5"); // returns "5"
$RETURN $PLUS(10, -5); // error, no unary operator '-' for strings