Re: Value

From: Stefan Ram <>
Date: 24 Feb 2008 15:26:16 GMT
Message-ID: <> (Stefan Ram) writes:
>This notion is so wide that it might help to explain,
>what is /not/ a value.

  I still would like to write more about values, from yet   another point of view. I hope that this time it will be the   most fundamental point of view:

  Whenever humans communicate, they refer to entities of a   universe of discourse. An entity is something that exists.

  But what exists? This is given by an agreement of the parties.   For example, when mathematicians talk about set theory, they   might agree to use the ZF axioms. These axioms include the   axiom »There is a set with no elements, called the empty set.«   Thus, they agree upon the existence of the empty set for this   discourse.

  A complete model contains entities and also assertions about   those entities, but it are those entities that are also being   referred to as »values«.

  In computer programming there are two models of importance:   The source code model and the run-time model.

    | Usually, those entities of the run-time model are called |
    | »values« that can be refered to by expressions of the    |
    | source-code model.                                       |

  Sometimes, these values also are known as »first-class values«.

  For example, in BASIC functions are not first-class values:   They are part of the source-code model (DEF FNA(X)=...), but   not of the run-time model (»FNA« is not an expression for FNA   whose value can be assigned to another name nor are there   function literals). In Scheme, functions are first-class values:   There are function literals; and functions can be assigned   to a name. Received on Sun Feb 24 2008 - 16:26:16 CET

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