There are two looping constructs and a conditional construct. The basic looping
construct has the form [...;...], either side of the semicolon may be
null. While the equate expression to the left of the semicolon is true do the
equate expression to the right of the semicolon. The expression on the left
must leave a boolean value on the stack. An example of this looping construct
was given earlier for the definition of strlen. The left and right
expressions can include anything, such as nested looping and conditional
constructs or function calls.
The other looping construct has the form (...). The expression between
the brackets is executed once for every record in the database. For example
here is the definition of a function to return the number of records in the
master database.
%%EQUATE NRECS 0>>NRECS(++NRECS>>NRECS)<<NRECS
The looping syntax can optionally include a colon suffix form. This allows
looping through a named database (if this is the master database then any
filtering conditions will be ignored).
This form is ():database where database is the name of
a valid loaded database (without the pathname or extension). Fields from other
databases cannot be accessed within the loop unless the -> syntax is
used, so if looping through a database other than the master database then
this form must be used within the loop to access fields of the master database.
Note that this applies even to nested equate calls within the loop body for
example.
The conditional construct has the form ?...:...;. This can take a field
name designator, in which case the behaviour is slightly different. The
action is to pop a boolean off the stack and if it is true to execute the
equate expression up to the colon, and if not to execute the equate expression
from the colon up to the semicolon. Each expression can be as complex as
required (including nested conditional and looping constructs, and function
calls) but need not have any contents. If the ? is immediately followed
by a field name and the colon and semicolon fields are null, then if the
contents of the field are empty the result is null, else the result is the
contents of the field. Below are two examples of the conditional construct.
%%EQUATE SUBDATE1 ?SUB_DATE:"In preparation"; %%EQUATE SUBDATE2 %SUB_DATE""=?"In preparation":%SUB_DATE;
Both the above conditions have the same action. If the %SUBDATE field
has a value push the value on the stack, else push the default string on the
stack.
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