add other haskell files

1 files changed, 28 insertions, 0 deletions

diff --git a/ch04_suffixtree.hs b/ch04_suffixtree.hs
new file mode 100644
index 0000000..a677ea4
--- /dev/null
+++ b/ch04_suffixtree.hs
@@ -0,0 +1,28 @@
+import Data.List (tails)
+
+suffixes :: [a] -> [[a]]
+suffixes xs@(_:xs') = xs : suffixes xs'
+-- as pattern.
+-- binds xs to the value on the right of the @
+suffixes _ = []
+
+-- same thing without as-pattern
+-- This will do a copy of the data, the as-pattern doesn't
+
+suffixesNoAs (x:xs) = (x:xs) : suffixesNoAs xs
+suffixesNoAs _ = []
+
+-- even better
+suffixes2 :: [a] -> [[a]]
+suffixes2 xs = init (tails xs)
+
+
+compose :: (b -> c) -> (a -> b) -> a -> c
+compose f g x = f (g x)
+
+suffixes3 xs = compose init tails xs
+
+suffixes4 = compose init tails
+
+-- no need to invent the compose function
+suffixes5 = init . tails