Function from symbol?

[jeremyc]

How can I:

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(define (greet who) (print "Hello " who))
(set 'lst '((name "John" who) (age 10)))
((lst 0 2) (lst 0 1))

In other words, reference a dynamic function inside a quoted list. The real reason for this is a process I created for parsing fixed width files:

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(define (special-conversion-function str) (do-something str))
(set 'layout '((name 10) (dob 6 special-conversion-function) (country 2)))
(import-data "file.txt" layout)

Now, the import-data function recognizes that dob requires a special conversion by the inclusion of another parameter in the fixed width format specification. I want import-data to then call the function "special-conversion-function" but I am failing to make it work.

Thanks,

Jeremy

[Lutz]

not sure what you mean, but you can pass functions as parameters like this:

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> (define (do-func foo arg) (foo arg))
(lambda (foo arg) (foo arg))
> (do-func upper-case "hello")
"HELLO"
> 

and you could pass user defined functions the same way.

Or when your function is inside a list as a symbol:

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> (define (do-func foo arg) (set 'func (eval (first foo))) (func arg))
(lambda (foo arg) (set 'func (eval (first foo))) (func arg))
> (do-func '(upper-case lower-case) "hello")
"HELLO"
> 

Lutz

[jeremyc]

not sure what you mean, but

Hm, my code was incorrect above. I simplified:

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(set 'lst '((name 20 trim) (age 5 int)))
(print ((lst 0 2) "JEREMY           ") "\n")

;; Desired output: JEREMY\n

Right now the output is:

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invalid function in function print : ((lst 0 2) "JEREMY           ")

[Lutz]

one more level to peel off :)

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>(set 'lst '((name 20 trim) (age 5 int)))  
(print ((eval (lst 0 2)) "JEREMY           ") "\n")
JEREMY
"\n"
> 

Lutz