One-sided limits aren’t implemented, and also some calculations don’t work

[roryokane]

@jackmaney was unable to post an Issue, so I’m posting it for him:

Looking through the README, the first thing that made me balk was the fact that the limit of 1/x as x->0 is not infinity. The limit doesn't exist! However:

• The limit as x goes to zero from the right of 1/x is infinity, and
• The limit as x goes to zero from the left of 1/x is negative infinity.

So, to quickly determine whether or not this was just a documentation issue, I installed Hilbert (and eventually succeeded) and tried to discover the syntax for one-sided limits:

Enjoy! -> lim[x->0+] 1/x

Enjoy! -> 

Hmmm...no output. Okay. Does any output work?

Enjoy! -> 3+2
5
Enjoy! -> 

Okay, good, we at least have that much... Hmmm...

Enjoy! -> lim[x->0^+] 1/x

Enjoy! -> 

Nope, that's not it, either. Poking at the source code, it doesn't seem as though one-sided limits are implemented.

Well, okay, how about a simpler limit?

Enjoy! -> lim[x->0] x+2

Enjoy! ->

Uhhh...okay, how about some differentiation?

Enjoy! -> d/dx(cos(x))
I'm so sorry, something wrong. Please feel free to report this.
Enjoy! -> 

This error message is of no use, and I have no idea what's going on, but this language appears to be broken.

[roryokane]

The calculations not working is probably the same problem as #66. But implementing one-sided limits sounds like a new and valid request.

[pqnelson]

Limits are an incredibly tricky thing to implement. Here's a great thesis on the very subject...a modest 152 pages, and it doesn't even scratch the surface of the subject!