How to determine if function is defined

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neil456
Posts: 12
Joined: Tue Feb 03, 2015 5:32 pm
Location: Kansas City, MO

How to determine if function is defined

Post by neil456 »

What is the correct way to determine that a function is defined. I am conditionally importing from a C lib and need to determine if the function was actually imported.

This is the import function.

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(define (pg_import_warn fun_name)
  (if (not (catch (import library fun_name "cdecl") 'pg_load_error))
    (println "pg_import WARNING: " pg_load_error)))
Import is done like this

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(pg_import_warn "PQescapeIdentifier")
Then sometime later i want to be able to do something like

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(if (function? PQescapeIdentifier)  (PQescapeIdentifier text) (SomeOtherFuncton text))
to use the function or not as the case may be.

Lutz
Posts: 5279
Joined: Thu Sep 26, 2002 4:45 pm
Location: Pasadena, California
Contact:

Re: How to determine if function is defined

Post by Lutz »

Just use the primitive? predicate, which works on built-in and imported functions:

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> (import "libc.dylib" "printf")
printf@7FFF8BF44910
> (primitive? printf)
true
>
or after loading postgres.lsp

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> (primitive? PgSQL:PQconnectdb)
true
>
for user-defined functions you would use lambda?

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> (define (double x) (+ x x))
(lambda (x) (+ x x))
> (lambda? double)
true

neil456
Posts: 12
Joined: Tue Feb 03, 2015 5:32 pm
Location: Kansas City, MO

Re: How to determine if function is defined

Post by neil456 »

Excellent, thanks
Neil

neil456
Posts: 12
Joined: Tue Feb 03, 2015 5:32 pm
Location: Kansas City, MO

Re: How to determine if function is defined

Post by neil456 »

Still having a problem with this. Consider the following example:

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(dolist (symb (symbols PgSQL))
	(if (lambda? symb)
		(println "found function: " symb)))
This does not work, so how do I get a list of symbols in a context that have lambda expressions assigned to them?

Lutz
Posts: 5279
Joined: Thu Sep 26, 2002 4:45 pm
Location: Pasadena, California
Contact:

Re: How to determine if function is defined

Post by Lutz »

The lambda? predicate is applied not to the symbol, but what is inside:

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(dolist (symb (symbols PgSQL))
 (if (lambda? (eval symb))
    (println "found function: " symb)))

found function: PgSQL:NULL?
found function: PgSQL:affected-rows
found function: PgSQL:clear-result
...
or shorter:

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> (filter (fn (s) (lambda? (eval s))) (symbols PgSQL))

(PgSQL:NULL? PgSQL:affected-rows PgSQL:clear-result PgSQL:close-db PgSQL:connect 
 PgSQL:connectdb PgSQL:data-seek PgSQL:databases PgSQL:error PgSQL:escape PgSQL:fetch-all 
 PgSQL:fetch-row PgSQL:fetch-value PgSQL:fields PgSQL:fnumber PgSQL:num-fields PgSQL:num-rows 
 PgSQL:query PgSQL:tables)
> 

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