Cannot recursively evaluate a function

[ruurd]

Enjoy! -> f(x)=x^2
x ** 2
Enjoy! -> f(4) 
16.0
Enjoy! -> f(f(f(4)))
I'm so sorry, something wrong. Please feel free to report this.   
Enjoy! -> f(f(4))
I'm so sorry, something wrong. Please feel free to report this.
Enjoy! -> f(16)
256.0

[jackmaney]

For that matter, composition of functions in general doesn't work well:

Hi guys,thank you for using Hilbert.
You need to execute "postulate zfc_analysis" if you wanna do real analysis.

Enjoy! -> postulate zfc_analysis
success! :)
Enjoy! -> f(x) = x^2
x ** 2
Enjoy! -> g(x) = x + 1
1 + x
Enjoy! -> f(g(2))
I'm so sorry, something wrong. Please feel free to report this.

It's also worth pointing out that there's a significant pause before the ambiguous "I'm so sorry, something wrong" error message.

[gogotanaka]

@jackmaney @ruurd Thank you so much! I'm sorry for delay.. That's true, function in Hilbert is not first class, but we should do..

Basically Hilbert aim to be pure logic programing language so it's difficult to handle higher-order function.

But I'll try it.