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From: thom@ecrc.de (Thom Fruehwirth)
Newsgroups: comp.lang.prolog
Subject: Re: general data structures are impossible
Message-ID: <1991Mar1.083108.27594@ecrc.de>
Date: 1 Mar 91 08:31:08 GMT
References: <1991Feb12.013413.24312@cs.ubc.ca> <4765@goanna.cs.rmit.oz.au> <1991Feb19.235323.7748@newcastle.ac.uk> <4818@goanna.cs.rmit.oz.au> <1991Feb28.153621.3524@newcastle.ac.uk>
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Reply-To: thom@ecrc.de (Thom Fruehwirth)
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Instead of encoding the problem with a data-structure, one could encode it
with a program-structure. Functions become predicates:

properties(snow,white).
properties(snow,crystalline).
properties(snow,cold).

substances(white,snow).
substances(white,paper).
substances(white,salt).
substances(crystalline,snow).
substances(crystalline,salt).
substances(crystalline,diamond).
substances(cold,snow).
substances(cold,liquid_nitrogen).
substances(frozen,snow).
substances(frozen,ice_cream).

Adding that snow melts ar 32 degrees F:

:- assert(melting_point(snow,32_degrees_F)).

Asking the melting point of something white and frozen:

:- substances(white,S),substances(frozen,S),melting_point(S,MP).

yields S=snow, MP=32_degrees_F.

Thom Fruehwirth