[Haskell-cafe] Stack overflow with my Trie implementation

Adrian Hey ahey at iee.org
Thu Apr 26 15:21:22 EDT 2007

Pete Kazmier wrote:
> I've modified my Norvig spelling corrector to use a trie instead of
> Data.Map in the hopes of improving performance.  Plus, this is fun and
> a great learning exercise for me.  Unfortunately, when I load my trie
> with a large amount of data, I get a stack overflow.  It's unclear to
> me why this is happening.  I specifically use foldl' to avoid this
> situation when building my trie.  Could someone shed some light on the
> situation for me?
> Here is the code:
>> module Main where 
>> import Data.List (foldl')
>> import Data.Maybe (maybe, fromMaybe)
>> import Prelude hiding (lookup)
>> import qualified Data.Map as M
>> data Trie a = T (Maybe a) (M.Map Char (Trie a)) deriving (Show)

Try making it strict in the Map field..

 > data Trie a = T (Maybe a) !(M.Map Char (Trie a)) deriving (Show)

Adrian Hey

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