[vox-tech] entering a prolog program?

[Chanoch (Ken) Bloom]

On Fri, 2010-11-19 at 20:05 -0800, Brian Lavender wrote:
> Can you type in axioms into prolog from the command line? All I seem to
> be able to do is load a program and query it. 
> 
> Can I just enter the following program at the prolog prompt?
> 
> factorial(0,1).
>   
> factorial(A,B) :-  
>            A > 0, 
>            C is A-1,
>            factorial(C,D),
>            B is A*D. 
> 
> 
> All I seem to be able to do is load it. I am using SWI prolog.
> 
> $ swipl
> ?- ['factorial.pl'].
> true.
> 
> If I try the following, I get an error. 
> 
> ?- factorial(0, 1).
> ERROR: toplevel: Undefined procedure: factorial/2 (DWIM could not correct goal)

Typing [user]. the way you typed ['factorial.pl']. will enter an
interactive rule entry mode. When you're finished with that mode, hit
Ctrl-D to return to query mode.

--Ken