diff --git a/ChangeLog.md b/ChangeLog.md
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--- /dev/null
+++ b/ChangeLog.md
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+# Changelog for hashmap-throw
+
+# v0.1.0.0
+
+* Add `lookupOrThrow` function for throwing from a hashmap.
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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+Copyright (c) 2020 Daniel Firth
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
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+++ b/README.md
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+# hashmap-throw
+
+`MonadThrow` variant of `Data.HashMap.lookup`.
diff --git a/hashmap-throw.cabal b/hashmap-throw.cabal
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--- /dev/null
+++ b/hashmap-throw.cabal
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+cabal-version: 1.12
+
+-- This file has been generated from package.yaml by hpack version 0.34.2.
+--
+-- see: https://github.com/sol/hpack
+
+name:           hashmap-throw
+version:        0.1.0.0
+synopsis:       Throw behaviour for hashmap lookup.
+description:    Adds a lookupOrThrow function that throws if the key is not found
+category:       Data structures
+author:         Daniel Firth
+maintainer:     dan.firth@homotopic.tech
+copyright:      2020 Daniel Firth
+license:        MIT
+license-file:   LICENSE
+build-type:     Simple
+extra-source-files:
+    README.md
+    ChangeLog.md
+
+library
+  exposed-modules:
+      Data.HashMap.Throw
+  other-modules:
+      Paths_hashmap_throw
+  hs-source-dirs:
+      src
+  build-depends:
+      base >=4.7 && <5
+    , exceptions
+    , hashable
+    , hashmap
+  default-language: Haskell2010
diff --git a/src/Data/HashMap/Throw.hs b/src/Data/HashMap/Throw.hs
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+++ b/src/Data/HashMap/Throw.hs
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+{- |
+   Module     : Data.HashMap.Throw
+   License    : MIT
+   Stability  : experimental
+
+lookupOrThrow function for HashMap.
+-}
+{-# OPTIONS_GHC -fno-warn-deprecations #-}
+module Data.HashMap.Throw (
+  lookupOrThrow
+, KeyNotFoundException(..)
+) where
+
+import Control.Monad.Catch
+import Data.Typeable
+import Data.Hashable
+import Data.HashMap as HM
+
+-- | Exception thrown when a key is not found in a hashmap.
+newtype KeyNotFoundException a = KeyNotFoundException a
+  deriving (Eq, Ord, Show)
+
+instance (Typeable a, Show a) => Exception (KeyNotFoundException a)
+
+-- | `HM.lookup` lifted to `MonadThrow` that throws `KeyNotFoundException`.
+lookupOrThrow :: (Eq a, Ord a, Show a, Typeable a, Hashable a, MonadThrow m) => a -> HashMap a b -> m b
+lookupOrThrow k m = case HM.lookup k m of
+                          Just x -> return x
+                          Nothing -> throwM $ KeyNotFoundException k