factorial to OutputForm

[Ralf Hemmecke]

Hmmmm, am somehow unable to find where the transformation to the
SExpression below happens. Does that have to do with '%specialDisp?
But even then I could not find a special treatment for 'factorial.

Background of this question.
I actually wanted to tweak Format1D locally so that it prints
factorial(a) instead of a!. But obviously ´'factorial is not a known
operator for OutputForm, so it is basically impossible to output
factorial differently.

Ralf

%%% (511) -> fa := factorial a

(511) a!
Type: Expression(Integer)

%%% (517) -> kfa := kernels(fa).1

(517) a!
Type: Kernel(Expression(Integer))

%%% (519) -> (kfa::OutputForm) pretend SExpression

(519) (CONCAT a !)
Type: SExpression

[Waldek Hebisch]

On Sat, May 18, 2024 at 09:21:27PM +0200, Ralf Hemmecke wrote:
> Hmmmm, am somehow unable to find where the transformation to the SExpression
> below happens. Does that have to do with '%specialDisp?
> But even then I could not find a special treatment for 'factorial.

This is regular '%display' property, set in BasicOperator.

> Background of this question.
> I actually wanted to tweak Format1D locally so that it prints
> factorial(a) instead of a!. But obviously ´'factorial is not a known
> operator for OutputForm, so it is basically impossible to output factorial
> differently.

'display' will set '%display' property to value that you give.
But this value will affect translation to OutputForm, so all
formatters.

--
Waldek Hebisch

[Ralf Hemmecke]

> This is regular '%display' property, set in BasicOperator.

Ah. Cool.
And just for reference...

The property is defined in op.spad like this.

dfact x == postfix("!"::Symbol::O, (ATOM(x)$Lisp => x; paren x))

The following code will then print "factorial(n)" as factorial(n).


newdfact(x:OF):OF == prefix("factorial"::Symbol,[x])
fa := factorial(n)
k := kernels(fa).1
op := operator k -- this is the factorial BasicOperator
display(op, newdfact)

> 'display' will set '%display' property to value that you give. But
> this value will affect translation to OutputForm, so all formatters.

Yes. But if one wants to achieve something locally, other parts maybe
uninteresting.

Thank you for your help.

Ralf