ESL allows you to specify a set of action statements to be performed if a given condition is true, and other action statements to be performed if the condition is false. You specify both the condition and the actions in a conditional action statement. A conditional action statement must begin with the if statement; it must contain a then clause; and it must end with the end if keywords. It can optionally contain an else clause.
Like other action statements, a conditional action statement can be specified within a response definition or an action routine definition. It can be specified within a loop statement, or even within another conditional action statement.
ESL first evaluates the boolean value specified in the if statement. The result of every boolean is either true or false. Remember that any boolean expression must be enclosed in parentheses.
If the boolean value is true, ESL performs the action statements specified in the then clause; the else clause, if specified, is ignored. If the boolean value is false, ESL performs the action statements specified in the else clause, if specified; the then clause is ignored.
After executing the then clause or the else clause, ESL continues normal program execution at the action statement, if any, immediately following the end if keywords.
Consider the following example:
response to Password
if (Code = "BN") then
copy 1 to Ncode
make Menu2 invisible
make Menu1 visible
else
copy 2 to Ncode
make Menu1 invisible
make Menu2 visible
end if
send Ncode to Dbase
Here, ESL first evaluates the boolean expression:
(Code = "BN")
If the variable Code contains the value "BN", the expression is true, and ESL executes the then clause and then ignores the else clause.
copy 1 to Ncode
make Menu2 invisible
make Menu1 visible
If the Code variable does not contain the value "BN", the expression is false, and ESL ignores the then clause and executes the else clause:
else
copy 2 to Ncode
make Menu1 invisible
make Menu2 visible
In either case, ESL continues execution at the statement following the end if keywords. Thus, in the example, ESL performs the following action statement whether or not Code contains "BN":
send Ncode to Database
This statement causes the value of the Ncode variable to be sent to the application program named Database.
The else clause is optional. For example, you can specify:
if ( (A > B) and (Count < MaxCount) ) then
append Count to Log
send Count to LogProg
end if
In this case, if the boolean value is false, ESL ignores the then clause and continues execution at the statement following the end if keywords.
