Re: On the textual order of rules

From: Michael Hanus <>
Date: Thu, 27 Mar 2014 17:40:04 +0100

On 03/26/2014 11:33 AM, Yi D wrote:
> Later, I found out that PAKCS compile Curry code to Prolog while KiCS2
> targets Haskell. So it seems that the behavior of PAKCS is due to the
> inheritance of the (mis-)feature of Prolog. But the question remains:
> What is the expected behavior of the Curry language we should expect?

You made a good point and I think the restriction due to the use
of Prolog's backtracking strategy should be better mentioned
in the PAKCS manual.

However, I'd like to emphasize that the difference between a language
specification (where some details are left open) and a corresponding
implementation is typical for many programming languages.
For instance, in the language definition of C++ (and also other
languages), the order of argument evaluation in function calls
is not specified, although this could be important for the computed
results (due to side effects). Different implementations
might fix an order in different ways. Or, in the Prolog ISO standard,
it is not specified whether a Prolog system has to perform an
occur check or not, although this could also influence the
computed results.


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