From: Gabriel Gonzalez <Gabriel439@gmail.com>
Date: Fri, 7 Feb 2014 15:08:47 +0000 (+0700)
Subject: Fixed `scan`
X-Git-Url: https://git.immae.eu/?a=commitdiff_plain;h=11645cdce20ff843caf8b53f82f2c32050fdd1fd;p=github%2Ffretlink%2Ftext-pipes.git

Fixed `scan`

The first `Char` of each output chunk is redundant (since it would have been
emitted by the previous chunk).  This removes the duplicate `Char`s.

Note that this bug was present in `pipes-bytestring` as well, and I fixed it
there, too.
---

diff --git a/Pipes/Text.hs b/Pipes/Text.hs
index eb72be2..4b2d2b0 100644
--- a/Pipes/Text.hs
+++ b/Pipes/Text.hs
@@ -485,13 +485,15 @@ filter predicate = P.map (T.filter predicate)
 scan
     :: (Monad m)
     => (Char -> Char -> Char) -> Char -> Pipe Text Text m r
-scan step begin = go begin
+scan step begin = do
+    yield (T.singleton begin)
+    go begin
   where
     go c = do
         txt <- await
         let txt' = T.scanl step c txt
             c' = T.last txt'
-        yield txt'
+        yield (T.tail txt')
         go c'
 {-# INLINABLE scan #-}