I am aware of the powerful features offered by the Common Lisp REPL. I am specifically using the SBCL implementation. However, I am not sure my REPL is setup properly and would like to know how to get more power out of the REPL.
For example, I wanted to find the power function to computer 2^3 = 8. This is called pow or power in many other languages. So I did:
CL-USER> (apropos 'pow)
POW
POWER
:OP-POWER-EXT (bound)
:POWERPC (bound)
SB-IMPL::*INTEGER-READER-BASE-POWER* (bound)
SB-IMPL::*POWER-CACHE* (bound)
SB-IMPL::+POWER-CACHE-INTEGER-LENGTH-LIMIT+ (bound)
SB-IMPL::COMPUTE-POWERS
SB-IMPL::POWER
SB-IMPL::POWERS-FOR-BASE (fbound)
SB-INT:POWER-OF-TWO-CEILING (fbound)
SB-KERNEL:%POW (fbound)
SB-KERNEL::POWER
SB-KERNEL:SCRUB-POWER-CACHE (fbound)
; No value
How would I view the documentation of any of these functions? Would I have to "import" any of these "libraries" before I view the documentation? Often I find that the documentation is missing, as the REPL will return nil. Where is the documentation? For example I did:
CL-USER> (documentation 'power 'function)
and it just returned NIL but as you can see from the list above given by apropos, power exists!
Summarizing:
SB-IMPL and SB-KERNEL libraries that are already imported?Thanks for all the help!
CL-USER> (documentation 'power 'function)and it just returned NIL but as you can see from the list above given by apropos, power exists!
The symbol power exists, but note that it's not bound or fbound like some of the other symbols are. Thus is doesn't have a function or value binding. Lots of symbols exist, even if they don't have a function or value binding. This can be particularly frustrating in apropos, because if you do (apropos 'name), then in reading the form, you've already ensured that there's a symbol name. Sometimes you'll see people use the uninterned symbol notation to avoid this problem. E.g.:
CL-USER> (apropos 'this-already-got-interned)
THIS-ALREADY-GOT-INTERNED
; No value
CL-USER> (apropos '#:but-this-didnt\!)
; No value
However, even if power did have a function or value binding, there's no guarantee that there'd be documentation available for it. Note that the documentation for documentation says:
Documentation strings are made available for debugging purposes. Conforming programs are permitted to use documentation strings when they are present, but should not depend for their correct behavior on the presence of those documentation strings. An implementation is permitted to discard documentation strings at any time for implementation-defined reasons.
That said, you can still try, and sometimes you'll get useful results:
CL-USER> (apropos '#:expt)
EXPT (fbound)
SB-C::EXPT-DERIVE-TYPE-AUX (fbound)
SB-C::EXPT-DERIVE-TYPE-OPTIMIZER (fbound)
...
; No value
CL-USER> (documentation 'expt 'function)
"Return BASE raised to the POWER."
In general, if you want to know more about an object, you can use describe (sds pointed this out before I did). The output isn't specifically defined, but it may well include the documentation:
CL-USER> (describe 'expt)
COMMON-LISP:EXPT
[symbol]
EXPT names a compiled function:
Lambda-list: (BASE POWER)
Declared type: (FUNCTION (NUMBER NUMBER) (VALUES NUMBER &OPTIONAL))
Documentation:
Return BASE raised to the POWER.
Source file: SYS:SRC;CODE;IRRAT.LISP
; No value
In general, these tools can be useful, but if you're looking for a particular function to achieve some task, Google is probably going to be more helpful unless you've already got a good idea of what you're looking for. After all, the first result in a Google search for “common lisp hyperspec exponent power” is a link to the page for expt.