[with patch] (sin + cos)(1) does not work

[robertwb]

Both sin and cos are functions of one (undetermined) variable, and can be called, but when one performs arithmetic on them this changes.

Maybe there should be a CallableSymbolicExpressionRing? with an unnamed variable that coerces into any CallableSymbolicExpressionRing? with a specified variable name?

sage: f = sin
sage: g = cos
sage: f(1)
sin(1)
sage: g(1)
cos(1)
sage: h = f+g
sage: h(1)
sin + cos # should be sin(1)+cos(1)
sage: f = 3*sin
sage: f(1)
3*sin # should be 3*sin(1)

[robertwb]

Better formatting:

sage: f = sin
sage: g = cos
sage: f(1)
sin(1)
sage: g(1)
cos(1)
sage: h = f+g
sage: h(1)
sin + cos         # should be sin(1)+cos(1), or at least throw an error
sage: f = 3*sin
sage: f(1)
3*sin             # should be 3*sin(1)

[robertwb]

Also should have

sage: f(x) = x^2
sage: f + sin
x |--> sin(x) + x^2

[robertwb]

See much discussion at  http://groups.google.com/group/sage-devel/browse_thread/thread/2f627fbe8d0f71c0

[mhansen]

This patch should be applied after #644.

[mabshoff]

Merged in 2.8.15.alpha1.