On 05/24/2007 01:23 AM, Gabriel Dos Reis wrote:
Ralf Hemmecke <[EMAIL PROTECTED]> writes:
| On 05/23/2007 06:50 PM, Bill Page wrote:
| > Quoting Martin Rubey <[EMAIL PROTECTED]>:
| >
| >> ... Igor Khavkine writes:
| >>
| >>> Can someone explain this syntax? Looking at the Axiom .spad files,
| >>> I see that it has general usage +/[...some list construction...].
| >>
| >> It is old syntax for reduce and should go away.
|
| I very much agree. The reason is that one should give an initial value
| otherwise you might be surprised.
I don't see why there should be a surprise.
Reduction through "/" is a functional on monoid operations, so one
should expect to give a unit element.
Sure. So whoever (which means a program) deals with "/" should first
check whether the second argument is a List over a monoid and that the
first argument is exactly *the* corresponding binary operation of that
particular monoid.
If I look at it that way, then "/" should be a unary operation since
what one currently writes as its first argument in
(+)/[1,2,3]
is redundant information. The monoid is specified by the argument of
List. (The problem arises if a set has two (or more) monoid structures
implemented, like Integer.)
Or are you saying that you have a domain (like Integer) and the first
argument then selects the monoid structure? What if I give a binary
function as the first argument which doesn't make the underlying set
into a monoid? That error cannot even be caught at runtime.
I am talking here about the compiler. If you have different plans with
the interpreter, I don't care at the moment, but for the compiler I see
no point why this form of "/" should be build into the (SPAD) language.
reduce on the other hand would want an initial value, or a value to
return when the list of operand is empty.
At least we agree on this.
Ralf
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