write as an expression?

I would like this function to be written as an expression.

function! SpellReplaceAll()
if &spell
try | spellr
catch
endtry
endif
endfun
nmap <F6> :call SpellReplaceAll()<cr>

How to make it work as an expression?

The following does not work :(
nmap <F6> &spell==1 ? spellr<cr>

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