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Clarion in general: Passing procedures as parameters 2006-02-10 -- Larry Sand Here's a trivial example of "how" you would use a procedure as a prototype.
It's difficult to come up with a non-trivial example using this technique.
It's more appropriate where you want to allow access to some data from
within a compiled module. A virtual method is very simlar and a better
choice in many circumstances. For a real world example of how a callback is
used in the Windows API, look in comp.lang.clarion for a thread with the
subject enumfonts. I posted an example on 2006.19.01 that uses a typed
procedure to prototype the callback procedure passed to the windows API.
Another similar example is the FileCallbackInterface in Clarion.
HTH,
Larry Sand
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Program
Map
TranslatorCallbackProc Procedure(Long MsgId),Type
Translate Procedure(TranslatorCallbackProc TraslateMessageId, Long MsgId)
enTranslator Procedure(Long MsgId)
esTranslator Procedure(Long MsgId)
End
nMsg Long
Code
nMsg = 1
Translate(enTranslator, nMsg)
nMsg = 2
Translate(esTranslator, nMsg)
Translate Procedure(TranslatorCallbackProc TraslateMessageId, long MsgId)
Code
TraslateMessageId(MsgId)
Return
enTranslator Procedure(Long MsgId)
Code
Case MsgId
Of 1
message('Hello')
Of 2
message('Goodbye')
End
Return
esTranslator Procedure(Long MsgId)
Code
Case MsgId
Of 1
message('Hola')
Of 2
message('Adiós')
End
Return
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