compiler limitation

I tried to ocmpile a (huge) lambda expression and got this error :

Error: Function size 398065 is too large.

The function is mostly a big trie structure doing (when (eq c
#\some_char) ...) and (case (c) (#\char_1 ... ) ... (#\char_n ...)).

What are the limitations of the compiler? Any idea to break this into
pieces?

Thanks for any clue,

-- 
Fabrice Popineau
------------------------
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