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From: ags@pucc-i (Seaman)
Newsgroups: net.lang.mod2
Subject: Re: circular procedure types
Message-ID: <277@pucc-i>
Date: Thu, 17-May-84 12:49:22 EDT
Article-I.D.: pucc-i.277
Posted: Thu May 17 12:49:22 1984
Date-Received: Sat, 19-May-84 00:40:06 EDT
References: <840@unm-cvax.UUCP> <670@ru-cs44.UUCP>
Organization: Purdue University Computing Center
Lines: 44

>  Our compiler (M2UNIX for the PDP-11) doesn't allow this program,
>  complaining as follows:
>  
>      1 MODULE circproc;
>      2 
>      3 TYPE Circular = PROCEDURE(Circular, CARDINAL): CARDINAL;
>   ****                                  ^74: type not declared
>      4 
>      5 PROCEDURE a(b: Circular;  x: CARDINAL): CARDINAL;
>      6 BEGIN
>      7     IF x = 0 THEN
>      8         RETURN 1
>      9     ELSE
>     10         RETURN x * b(b, x - 1)
>     11     END
>     12 END a;
>     13 
>     14 PROCEDURE Factorial(n: CARDINAL): CARDINAL;
>     15 BEGIN
>     16     RETURN a(a, n)
>   ****              ^128: type incompatibility
>     17 END Factorial;
>     18 
>     19 END circproc.

I am not familiar with M2UNIX, but I'll bet it's a one-pass compiler.
Volition Systems (also one-pass) gives the same error on line 3 but
does not complain about line 16.
>  
>  I guess you could do it with two procedures and two definition modules
>  but ...
>  
>  -- 
>  Adrian Pell		({vax135,mcvax,edcaad}!ukc!ru-cs44!adrian)
>  Computer Science Dept.
>  University of Reading
>  UK
-- 

Dave Seaman
..!pur-ee!pucc-i:ags

"Against people who give vent to their loquacity 
by extraneous bombastic circumlocution."