PASCAL, Declaration Section, Routine Declaration, formal_parameter_list
*Conan The Librarian (sorry for the slow response - running on an old VAX)
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VMS Help PASCAL, Declaration Section, Routine Declaration, formal_parameter_list *Conan The Librarian (sorry for the slow response - running on an old VAX) |
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A formal parameter is located in the header of the routine
declaration, and consists of input parameters, output
parameters, and routine parameters. A routine uses input
parameters to obtain values; it uses output parameters to return
values; and it uses routine parameters to call another routine
named by a formal parameter.
The formal parameter establishes the semantics, the data type,
and the required passing mechanism of the parameter. See the
"Compaq Pascal Language Reference Manual" for more information
on parameter passing mechanisms.
Syntax:
[[({ {value-parameter-spec | variable-parameter-spec |
routine-parameter-spec | foreign parameter-spec} };...)]]
The specific format depends on the semantics (value, variable,
routine, or foreign) of the formal parameter you are declaring.
A formal value parameter represents a local variable within the
called routine. When you specify value semantics, the address
of the actual parameter is passed to the called routine, which
then copies the value from the specified address to its own
local storage. The routine then uses this copy. The copy is
not retained when control returns to the calling block.
Therefore, if the called routine assigns a new value to the
formal parameter, the change is not reflected in the value of
the actual parameter.
Syntax:
{identifier},... : [[attribute-list]]
{type-id | conformant-parameter-syntax |
undiscriminated-schema-name}
[[:= [[mechanism-specifier]] default-value]]
A formal variable parameter represents another name for a
variable in the calling block. It is preceded by the reserved
word VAR. When you specify variable semantics, the address of
the actual parameter is passed to the called routine. In
contrast to value semantics, the called routine directly
accesses the actual parameter. Thus, the routine can assign a
new value to the formal parameter during execution and the
changed value is reflected immediately in the calling block (the
value of the actual parameter changes).
Syntax:
VAR {identifier},... : [[attribute-list]]
{type-id | conformant-parameter-syntax |
undiscriminated-schema-name}
[[:= [[mechanism-specifier]] default-value]]
To write a routine that invokes another routine whose effect is
not determined until the program is executed, use routine
parameters. To declare a procedure or a function as a formal
parameter to another routine, you must include a complete
routine heading in the formal parameter list. You can also
associate a foreign mechanism specifier and a default value with
a formal procedure or function parameter.
Syntax:
[[attribute-list]] PROCEDURE procedure-id [[formal-parameter-list]]
[[ := [[mechanism-specifier]] default-value ]]
or
[[attribute-list]] FUNCTION function-id [[formal-parameter-list]] :
[[attribute-list]] result-type-id
[[ := [[mechanism-specifier]] default-value ]]
When declaring an external routine (one written in a language
other than Pascal) that is called by a Compaq Pascal routine,
you must specify not only the correct semantics but the correct
mechanism as well. To allow you to obtain these passing
mechanisms, Compaq Pascal provides foreign mechanism specifiers
and the passing mechanism attributes.
See the "Compaq Pascal Language Reference Manual" for complete
details on formal parameter semantics.
Additional Information (explode) :
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