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authorVincent Ambo <mail@tazj.in>2020-06-16T00·05+0100
committerVincent Ambo <mail@tazj.in>2020-06-16T00·05+0100
commit2edb963b97867b27f68efac8d05bf966077b0b01 (patch)
treec3bb279dfd4330e09a0af6ef4e84ff8a9a3bc7ad /users/glittershark/xanthous/src/Xanthous/Util/Comonad.hs
parent91f53f02d8479303910abfd3f3690d3ef27e6c4b (diff)
parent53b56744f4335c038724a1bcffc27a7eb8cf6a6d (diff)
Add 'users/glittershark/xanthous/' from commit '53b56744f4335c038724a1bcffc27a7eb8cf6a6d' r/978
git-subtree-dir: users/glittershark/xanthous
git-subtree-mainline: 91f53f02d8479303910abfd3f3690d3ef27e6c4b
git-subtree-split: 53b56744f4335c038724a1bcffc27a7eb8cf6a6d
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+--------------------------------------------------------------------------------
+module Xanthous.Util.Comonad
+  ( -- * Store comonad utils
+    replace
+  , current
+  ) where
+--------------------------------------------------------------------------------
+import Xanthous.Prelude
+--------------------------------------------------------------------------------
+import Control.Comonad.Store.Class
+--------------------------------------------------------------------------------
+
+-- | Replace the current position of a store comonad with a new value by
+-- comparing positions
+replace :: (Eq i, ComonadStore i w) => w a -> a -> w a
+replace w x = w =>> \w' -> if pos w' == pos w then x else extract w'
+{-# INLINE replace #-}
+
+-- | Lens into the current position of a store comonad.
+--
+--     current = lens extract replace
+current :: (Eq i, ComonadStore i w) => Lens' (w a) a
+current = lens extract replace
+{-# INLINE current #-}