> Procedural types


 Procedural types

Standard Pascal treats procedures and functions strictly as program parts that can be executed through procedure or function calls.

Borland Pascal has a much broader treatment of procedures and functions. Through procedural types, it allows procedures and functions to be treated as objects that can be assigned to variables and passed as parameters.

A procedural-type declaration specifies parameters and, for a function, result type.

The syntax for a procedural-type declaration is identical to procedure or function header, except that it omits the identifier after the procedure or function keyword.


   Proc = procedure;
   SwapProc = procedure(var X, Y: Integer);
   StrProc = procedure(S: string);
   MathFunc = function(X: Real): Real;
   DeviceFunc = function(var F: text): Integer;
   MaxFunc = function(A, B: Real; F: MathFunc): Real;

Parameter names in a procedural-type declaration to not affect the meaning of the declaration.

Borland Pascal does not let you declare functions that return procedural-type values.

A function result value must be a string, Real, Integer, Char, Boolean, Pointer, or a user-defined enumeration.

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