Global shelves and constants may be pre-defined so that they may be referenced before their initializers are known. This provides the programmer with more options for organizing code. Pre-definitions must be used when declaring shelves or constants in an interface module.
A shelf pre-definition is indicated by the keyword elsewhere:
constant stream month-names size 12 elsewhere
When month-names is finally defined, it must have exactly 12 values:
constant stream month-names size 12 elsewhere define function output-month-names as repeat over month-names output month-names || '%n' again ;... constant stream month-names size 12 initial { "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December" } process output "Months:%n" output-month-names
In this case, the function output-month-names must be defined some time after the pre-definition for month-names because it makes reference to it. It cannot be executed until month-names is defined, because that is what makes the values on the shelf available.
A shelf pre-definition must match the definition in every way, except that it cannot specify initial values, and, if the shelf is variable-sized, the pre-definition cannot specify an initial-size. One way to think about this, at least for global shelves, is that the pre-definition specifies those properties of the shelf that cannot be changed later.
Examples:
constant month-names size 12 elsewhere; pre-definition global stream user-names variable elsewhere ; pre-definition global stream admin-users variable elsewhere ; pre-definition global stream months-with-r variable to 12 elsewhere; pre-definition constant stream month-names size 12 initial { "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December" } global stream user-names variable ; definition global stream admin-users variable initial {"harold", "maude"} global stream months-with-r initial-size 0 variable to 12 process-start repeat over month-names set new months-with-r to month-names when month-names matches unanchored ul "r" again