HTMLBusiness Expressions
HTMLBusiness expressions are similar to those used in C, C++ or Java.
From ITS 2.2, there are new rules for
-
Operator priority
-
Operator associativity
Operator Priority
Prior to ITS 2.2, operator priority rules in HTMLBusiness were not always intuitive, and differed from C, C++, or Java.
For instance, the || operator had priority over the == operator, so ITS developers had to use parentheses unnecessarily to clarify priority.
Instead of writing
`if (a==1 && b==2)`
it was necessary to write
`if ((a==1) && (b==2))`
Otherwise, the HTMLBusiness interpreter would interpret the expression as
`if (a==(1 && b)== 2)`
From ITS 2.2, operator priority has been redefined to match that used by the programming languages C, C++, and Java:
Currently, HTMLBusiness provides the following operators, listed in decreasing order of priority:
|
Operator |
Priority |
|
++, -- |
1 |
|
*, /, % |
2 |
|
+, -, & |
3 |
|
==, !=, >, <, >=, <= |
4 |
|
&&, || |
5 |
If you need a different evaluation sequence, you must use parentheses. Operators with the same priority are evaluated from left to right.
Operator Associativity
Prior to ITS 2.2, operator associativity also differed from C, C++, or Java in some (but not all) cases, since terms were evaluated from right to left (rather than from left to right).
From ITS 2.2, operator associativity has been changed to evaluate from left to right, in order to achieve consistency with other programming languages.
Therefore, the expression
`8/2*4`
is now evaluated as
`(8/2)*4` (==16)
instead of
`8/(2*4)` (==1).
Expression Syntax
The syntax summarized in the table below specifies the currently allowed forms of expression:
-
Operators with identical priority are grouped and evaluated from left to right.
-
If you want to enforce a different evaluation sequence, you must use parentheses.
|
Nonterminal |
Derivation |
|
expression |
simpleexpr [compop simpleexpr] |
|
simpleexpr |
term { addopr simpleexpr} |
|
term |
factor { mulopr factor} |
|
factor |
( ! | ++ | --) factor ( expression) | function call | assignment | lvalue [++ | -- ] | constant |
|
function call |
internalfn ( argument {, argument}) | externalfn ( expression {, expression}) |
|
internalfn |
write | writeEnc | wgateURL | archiveURL | imageURL | mimeURL | assert |
|
mulopr |
* / % && |
|
addopr |
+ - & || |
|
compop |
== | != | > | < | >= | <= |
The following syntax conventions are observed in tables:
|
Notation |
Description |
Usage |
|
[...] |
Square brackets |
Optional derivations. |
|
{...} |
Braces |
Contain zero or number of repetitions of an expression. |
|
| |
Vertical line |
Alternative derivatives ( OR). |
|
(...) |
Parentheses |
Combine components where uniqueness is not guaranteed. |
Value Types
A variable can only be a string or an integer.
The following are examples of correct expressions:
vbcom-kunde
nCustomers % 10
!fExists
a > b*2+1
name != "Walt"&" "&"Whitman"
(x -y) * (a+b) & " US$"
cond1 && (cond2 || cond3) && cond4