Getting pitch out of a pair

[address@hidden]

I store two pitches in a pair variable
x = #'(b . cis')

But then I want to retrieve each one as a  pitch in a music-function
foo = #(define-music-function (parser location bar) (ly:music?)
        (define from (car x))
        (define to (cdr x))
        #{
                \transpose $from $to $bar
        #}

but when I use this
\foo a

I get Expecting pitch, found (quote b)

So what am I doing wrong and how can I do it right?

// Anders
PS! The foo function is just a snippet the real function does a bit more...
--
English isn't my first language.
So any error or strangeness is due to the translation.
Please correct my English so that I may become better.