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MathGroup Archive 2005

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Re: Types in Mathematica thread

  • To: mathgroup at smc.vnet.net
  • Subject: [mg62833] Re: Types in Mathematica thread
  • From: Jon Harrop <usenet at jdh30.plus.com>
  • Date: Tue, 6 Dec 2005 00:04:57 -0500 (EST)
  • References: <dmp9na$hi2$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Kris Carlson wrote:
> 1. Everything is an expression, which is wonderful in its simplicity. Thus
> since everything is of the form head[body], everything is typed in at
> least one way via the head, and everything can be tested for its type, eg,
> with Head[expr].

Trying to define the type of a Mathematica expression as the result returned
by Head is not a great idea because the result of Head is itself an
arbitrary expression. For example, this definition of "type" becomes
useless in the presence of currying.

> ...
> 5. Mathematica excels in pattern-matching,

Mathematica certainly provides a lot of functionality in its pattern matcher
but pattern matchers in other languages provide many benefits not found in
Mathematica:

1. Exhaustiveness checking
2. Redundancy checking
3. Well-defined performance

For example, the conventional implementation of a function to compute the
length of a list has quadratic complexity in Mathematica:

f[{}] := 0
f[{h_, t___}] := 1 + f[{t}]

However, this may get fixed in the future.

> 7. Downvalues are "default" function structures, or "common" functions, or
> "built-in function" structures, or "broadest class" functions. Upvalues
> are "special case" functions, or "user-defined" functions / modifications
> of built-in or default functions, or "narrow-case" functions, or
> "context-dependent" functions. (This latter is especially important for AI
> and for a general understanding of the universe.)

The fact that Mathematica distinguishes between up- and down-values is
really incidental (a historical artefact). So I think you're over-analysing
it.

> What is overloading? Mathematica does not provide functions such as
> plusII[ i1_Integer, i2_Integer], plusRR[ r1_Real, r2_Real ], plusRI[
> r_Real, i_Integer }, and so forth. You would not be using it if it did
> [because it would be a big pain in the rear like we find in other
> "strongly typed" languages--KWC].

Some strongly typed languages, yes.

I still use other languages that do separate ints and floats into separate
types.

> The standard arithmetic operations are overloaded: they work with data of
> many different types and perform conversions as necessary.

Without a definition of "type", such statements have no value.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/products/ocaml_for_scientists/chapter1.html


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