lisp - should be a lambda expression

Question

I'm trying to return (values str ((+ x 3) y)) from the function it resides in.

code snippet:

(if (<my condition>)
    (values str ((+ x 3) y))
    (values str ((+ x 2) y)))

gives error:

(+ X 3) SHOULD BE A LAMBDA EXPRESSION

but (values str (y (+ x 3))) works fine.

why?

Can you add a little more context? What are the values of x and y here? It looks like y is acting like a function. — munk
– munk, Commented Mar 4, 2014 at 5:40
perhaps (y (+ x 3)) should be literal '(y (+ x 3)) or perhaps missing an operator (* y (+ x 3))? Perhaps you have define the function y? — Sylwester
– Sylwester, Commented Mar 5, 2014 at 20:42

sds · Accepted Answer · 2014-03-04 19:01:15Z

6

The S-expression ((+ x 3) y) cannot be evaluated because the first list element is not funcallable (it should name a function or be a lambda expression).

So, to avoid evaluation, you need to quote it:

(if (<my condition>)
    (values str '((+ x 3) y))
    (values str '((+ x 2) y)))

Then you will return a list of length 2 (containing a list of length 3 and a symbol y) as your second value. If, however, you want to return the values of (+ x 2) and y in the list, you will want to do something like

(values str (list (+ x (if <condition> 3 2)) y))

or maybe return 3 values instead of 2:

(values str
        (+ x (if <condition> 3 2))
        y)

On the other hand, y is a symbol, which, apparently, names a function in your image, so (y (+ x 3)) evaluates fine (it calls function y on the result of adding 3 to x).

edited Mar 4, 2014 at 19:01

answered Mar 4, 2014 at 14:19

sds

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