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From: heiser@iis.UUCP (Gernot Heiser)
Newsgroups: comp.lang.modula2
Subject: Re: Re^2: Error in PD Modula-2 compiler? Or just in my brain?
Message-ID: <1130@eiger.iis.UUCP>
Date: 1 Jun 89 19:04:20 GMT
References: <340@actisb.UUCP> <1090@gmdzi.UUCP> <1231@infbs.UUCP>
Reply-To: heiser@iis.ethz.ch (Gernot Heiser)
Organization: ETH Zuerich, Switzerland
Lines: 30
Summary:
 Expires:

In article <1231@infbs.UUCP> neitzel@infbs.UUCP (Martin Neitzel) writes:
>kloppen@gmdzi.UUCP (Jelske Kloppenburg) writes:
>1. VAL is _not_ a "type transfer function" [pim3, 12.], but a standard
>   procedure [pim3, 10.2].  Especially, VAL conversions guarantee to
>   preserve the value, which may involve changes in the representation.
>   Type transfers, on the other hand, do not.
>
>2. Usage of VAL doesn't require SYSTEM.  (pim3: "Standard procedures are
>   predefined.")

Correct according to THE BOOK. However, N.W. sometimes changes his mind too. In
particular about three years ago he decided that use of the ("unsafe") type
transfer functions should be discouraged. Furthermore being a system dependent
thing, type coercions should really be designated as such by having to be
imported from SYSTEM.

In addition he apparently also decided that the ("safe") type casts as
originally provided by the standard function VAL were unnecessary. So he ended
up doing away with type transfer functions, assigning their former meaning to
VAL and putting the latter into SYSTEM. That's the way it is implemented in all
the (one pass) compilers that left ETH in the last few years.

Last I heard from the standardisation commitee is that they were undecided
which of the two "standards" to follow (or even come up with a third
alternative).
-- 
Gernot Heiser                   Phone:       +41 1/256 23 48
Integrated Systems Laboratory   CSNET/ARPA:  heiser%iis.ethz.ch@relay.cs.net
ETH Zuerich                     UUCP (new):  heiser@iis.uucp
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