Initializing help system before first use

isdefined

Purpose
Check whether an entity is defined.
Synopsis
function isdefined(v:reference):boolean
Argument
v 
A variable of a reference type
Return value
true if the provided entity is defined.
Example 
declarations
 f: function(real):real
 u: any
end-declarations
writeln(isdefined(u))    ! = false
u:=1.5
writeln(isdefined(u))    ! = true

writeln(isdefined(->f))  ! = false
f:=->cos
writeln(isdefined(->f))  ! = true
reset(->f)
writeln(isdefined(->f))  ! = false
Further information
This function returns true if the provided entity is not a NULL reference and, in the case of a union or a subroutine, if it has been assigned a value.

Parent Topic Predefined functions and procedures

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