This code, from YAHT (Section 8.4.2, PDF pg. 119 of 192) seems to have a problem. Code below.
Michael
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[michael@localhost ~]$ ghci
GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
Prelude> :l graph
[1 of 1] Compiling Main ( graph.hs, interpreted )
graph.hs:6:24: lexical error at character '\8217'
Failed, modules loaded: none.
==============
Prelude> data Graph v e = Graph [(Int,v)] [(Int,Int,e)]
search :: Graph v e -> Int -> Int -> Maybe [Int]
search g@(Graph vl el) src dst
| src == dst = Just [src]
| otherwise = search’ el
where search’ [] = Nothing
search’ ((u,v,_):es)
| src == u =
case search g v dst of
Just p -> Just (u:p)
Nothing -> search’ es
| otherwise = search’ es
|