Re: Procedure Parameters in Ada

[cjh@petsd.UUCP (Chris Henrich)]

[]
In article <8606042209.AA23350@vrdxhq.uucp> drm1@vrdxhq.UUCP (Donn Milton) writes:
>Many people seem to be unaware of a major problem entailed by
>procedures as parameters.  That is, when procedures are allowed
>as parameters, strong type-checking becomes generally undecidable
>(not just hard) UNLESS recursive mode-type declarations (a la Algol 68)
>are introduced.  

Procedure & function parameters are part of standard Pascal.
In the current ANSI/ISO standard (though not in the old book by
Jensen and Wirth) a certain degree of type checking is
mandated.  I know of at least one compiler which provides it.
It is not difficult; the routine which checks for
compatibility of types may have to call itself recursively.

These possibilities occur to me:
(a) what ANSI/ISO mandates is not "strong" in Donn Milton's
sense;

(b) something in Pascal corresponds to "recursive mode-type
declarations;

(c) for some other reason, the theorem being cited is beside
the point.

It may be worth while to note that subprograms as *variables*
have worse problems than subprograms as *parameters.*
Regards,
Chris

--
Full-Name:  Christopher J. Henrich
UUCP:       ...!hjuxa!petsd!cjh
US Mail:    MS 313; Concurrent Computer Corporation;
            106 Apple St; Tinton Falls, NJ 07724
Phone:      (201) 758-7288
Concurrent Computer Corporation is a Perkin-Elmer company.