Scheme function help - modifying note durations

[Shashank Raja]

I want to write a scheme function that doubles a note such that the 
pitch (let's call it 'x') is retained, but the respective durations are 
such that {x8.. x32} is displayed. 
Since \displayMusic{ c'8.. c'32 } outputs this:
https://raw.github.com/gist/3843324/f77790c4917337539936584ae65bb886f804edec/gistfile1.ly

My attempt based wholly on the Lilypond Scheme docs is as follows:
https://raw.github.com/gist/3843324/15d0b07d567370f69631f68194e71bc5a62c6610/minimal.ly

However, I get this error upon compiling:
https://raw.github.com/gist/3843324/0e5c741648ec02eddf2e561aa3d69f0b114acde9/error%20output

Also, in the part of the error which says 
 (#<Duration 32 > . #<Duration 4 >)

the 4 changes based on the argument to the \myfunc function; i.e. \myfunc c128 would result in (with snipping, of course):
 (#<Duration 32 > . #<Duration 128 >)

What am I doing wrong? Can someone point out my (evidently conceptual) error(s) here, and show me in the direction of how to fix it? Thanks in advance.