Re: simple vs complex languages

vbdis@aol.com (VBDis) writes:
|> nmm1@cus.cam.ac.uk (Nick Maclaren) schreibt:
|>
|> >There are a fair number of languages around where a function doesn't
|> >have to exist even when it is called, and a missing function will be
|> >automatically converted into some other construction (e.g. a call to
|> >an external program). This can be useful, as any shell programmer can
|> >witness :-)
|>
|> And the user has to pray each time before running such a program,
|> because nobody can tell him what it /will/ do. Such code can only give
|> hints on what the program /should/ do... ;-)


Yes. You always have to pay something for flexibility and
functionality. My view of such languages is that such 'external'
calls are best modelled in the same way as interactive human input.
I.e. you can constrain and check them as for what the user types, but
you have to regard them as completely unpredictable beyond what you
have constrained or checked.


Constraining the syntax is standard technology, and I remember some
people working on languages a couple of decades back that did some
limited constraining of the semantics - e.g. a function (or even
program) had to declare what exceptions it might raise and what
resources it might use (both of which CAN be checked). Does anyone
know if anything came of that?


Regards,
Nick Maclaren.

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