lisp: lambda scope

Question

I want to implement filter function that would filter a list based on a condition

(defun filter (func xs)                                                          
  (mapcan                                                                        
    (lambda (x)                                                                  
      (when (func x) (list x))) xs ))

but I get an error:

*** - EVAL: undefined function FUNC

I thought that lambda should see func. How to pass func to lambda correctly?

I use CLISP.

You might also want to have a look at the function `REMOVE-IF-NOT` which does exactly this. — Elias Mårtenson, Oct 31 '12 at 08:34

score 5 · Accepted Answer · edited May 23 '17 at 10:25

5

You want

(when (funcall func x) (list x))

instead of

(when (func x) (list x))

More information about function vs. variable namespace:

edited May 23 '17 at 10:25

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answered Oct 30 '12 at 09:55

finnw

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lisp: lambda scope

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