Re: Nested Lambda function gives error in common lisp, guile, emacs lisp but works in scheme. Why?

[Pascal Costanza]

gnuist006@hotmail.com wrote:
> Please explain the below errors:

> [1]> (((lambda (a) (lambda (b) (list a b))) 1) 2)
>
> *** - EVAL: ((LAMBDA (A) (LAMBDA (B) (LIST A B))) 1) is not a function
> name; try using a symbol
>       instead
> The following restarts are available:
> USE-VALUE      :R1      You may input a value to be used instead.
> ABORT          :R2      ABORT
>
>
> Similar errors in emacs lisp.

Common Lisp (and presumably Emacs Lisp) is a Lisp-2, which means that 
function positions are evaluated differently than value positions. In 
order to treat a first-class value as a function, you have to shift it 
via FUNCALL. In order to yield a function as a first-class value, you 
have look it up with FUNCTION.

Your code works in Common Lisp when you do this:

(funcall (funcall (lambda (a) (lambda (b) (list a b))) 1) 2)

This looks inconvenient, but there are good reasons why one might prefer 
a Lisp-2 over a Lisp-1 (like Scheme). See 
http://www.dreamsongs.com/Separation.html

If you google for Lisp-2 and Lisp-1, you will find more information. 
There have been a number of discussions about this in comp.lang.lisp.


Pascal

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