Hold context

[kcrisman]

Now that Pynac will support 'hold' of symbolic expressions, like

sage: tan(pi/12,hold=True)
tan(1/12*pi)

we might want a 'context' for this.
The ticket enables the following:

        sage: tan(1/12*pi)    
        -sqrt(3) + 2
        sage: with hold:
        ....:     tan(1/12*pi)
        ....:     
        tan(1/12*pi)
        
        sage: with hold:
        ....:     sin(0)
        ....:     cos(0)
        ....:     
        sin(0)
        cos(0)
        sage: hold.start()
        sage: sin(0)
        sin(0)
        sage: cos(0)
        cos(0)
        sage: hold.stop()
        sage: sin(0)
        0

Depends on #23820

CC: @burcin @eviatarbach

Component: symbolics

Author: Ralf Stephan

Branch/Commit: 3ad332c

Reviewer: Emmanuel Charpentier

Issue created by migration from https://trac.sagemath.org/ticket/10035

[jasongrout]

comment:1

Can you give a code sample of what you mean?

[kcrisman]

comment:2

Replying to @jasongrout:

Can you give a code sample of what you mean?

No, because this is really a followup to another ticket. I'll cc: Burcin in, though he probably already gets it given the component. I imagine something like

sage: context('hold') # or whatever the usual syntax is for such things - Sage doesn't have any yet
sage: a = tan(pi/12)
sage: a
tan(pi/12)

as opposed to evaluating it.

[burcin]

comment:3

I was thinking of something like:

sage: with hold:
....:     t = tan(pi/2)
....:
sage: t
tan(pi/12)
sage: tan(pi/12)
-sqrt(3) + 2

[jasongrout]

comment:4

That would be awesome!

[jpflori]

comment:5

Replying to @jasongrout:

That would be awesome!

But with such a construction it is not obvious how to simplify 't' without going through Maxima as suggested in #10034

sage: with hold: 
....:     t = tan(pi/2) 
....: 
sage: t tan(pi/12) 
sage: t.eval() #or t.unhold() or whatever 
-sqrt(3) + 2

[kcrisman]

comment:6

#11776 seems to be asking for something very similar.