Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ukma!gatech!hubcap!billwolf%hazel.cs.clemson.edu
From: billwolf%hazel.cs.clemson.edu@hubcap.clemson.edu (William Thomas Wolfe,2847,)
Newsgroups: comp.lang.misc
Subject: Re: Learning Ada
Message-ID: <6359@hubcap.clemson.edu>
Date: 31 Aug 89 15:54:48 GMT
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From hutch%citron.cs.clemson.edu@hubcap.clemson.edu (David Hutchens):
> Of course there is the classic (from Ada): "Gee I need the cube of X":
> 	z := x ** 3;
> which, of course (:-) generates the message "Ambiguous Expression".
> 
> The beginning student might be slightly confused by the reason:
>    "The constant 3 is overloaded (as both integer and short integer)
>     and there are 2 distinct ** operators, so the compiler doesn't
>     know which to pick!"

   Actually, the compiler does know... the exponentiation operator's
   right operand is required to be of type INTEGER, as per Appendix
   C, page 2, paragraphs 6 & 7 of ANSI/MIL-STD-1815A:

      -- function "**" (LEFT : INTEGER; RIGHT : INTEGER) return INTEGER;

      -- An implementation may provide additional predefined integer 
      -- types... The specification of each operator... for any additional
      -- predefined integer type, is obtained by replacing INTEGER by the
      -- name of the type in the specification of the corresponding
      -- operator of the type INTEGER, except for the right operand 
      -- of the exponentiating operator.
  
   Similarly, 4.5.6.4 states:

      The highest precedence exponentiating operator ** is predefined
      for each integer type and for each floating point type.  In either
      case the right operand, called the exponent, is of the predefined
      type INTEGER. 

   Thus, the constant 3 is not overloaded; it is clearly of type INTEGER. 

   In view of the fact that the "classic" case described is actually a
   double violation of the Ada reference manual, it seems highly probable
   that this is an error which is traceable either to the user defining 
   an unnecessary overloading of "**", or to an unvalidated compiler. 


   Bill Wolfe, wtwolfe@hubcap.clemson.edu