diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,30 @@ +Copyright (c) 2015, Jeremy Shaw + +All rights reserved. + +Redistribution and use in source and binary forms, with or without +modification, are permitted provided that the following conditions are met: + + * Redistributions of source code must retain the above copyright + notice, this list of conditions and the following disclaimer. + + * Redistributions in binary form must reproduce the above + copyright notice, this list of conditions and the following + disclaimer in the documentation and/or other materials provided + with the distribution. + + * Neither the name of Jeremy Shaw nor the names of other + contributors may be used to endorse or promote products derived + from this software without specific prior written permission. + +THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. diff --git a/Setup.hs b/Setup.hs new file mode 100644 --- /dev/null +++ b/Setup.hs @@ -0,0 +1,2 @@ +import Distribution.Simple +main = defaultMain diff --git a/example/BrokenTuple.hs b/example/BrokenTuple.hs new file mode 100644 --- /dev/null +++ b/example/BrokenTuple.hs @@ -0,0 +1,4 @@ +module Main where + +main :: IO () +main = print $ length ('a', 'b') diff --git a/example/GoodTuple.hs b/example/GoodTuple.hs new file mode 100644 --- /dev/null +++ b/example/GoodTuple.hs @@ -0,0 +1,8 @@ +module Main where + +import Safe.Length (safeLength) +import Data.Proxy (Proxy(..)) + +main :: IO () +main = print $ safeLength (Proxy :: Proxy (Char, Char)) ('a', 'b') + diff --git a/example/List.hs b/example/List.hs new file mode 100644 --- /dev/null +++ b/example/List.hs @@ -0,0 +1,7 @@ +module Main where + +import Data.Proxy (Proxy(..)) +import Safe.Length (safeLength) + +main :: IO () +main = print $ safeLength (Proxy :: Proxy [Char]) ['a', 'b'] diff --git a/example/NestedList.hs b/example/NestedList.hs new file mode 100644 --- /dev/null +++ b/example/NestedList.hs @@ -0,0 +1,8 @@ +module Main where + +import Data.Proxy (Proxy(..)) +import Safe.Length (safeLength) + +main :: IO () +main = print $ safeLength (Proxy :: Proxy [[Char]]) (head [['a', 'b', 'c']]) + diff --git a/example/OldList.hs b/example/OldList.hs new file mode 100644 --- /dev/null +++ b/example/OldList.hs @@ -0,0 +1,8 @@ +module Main where + +import GHC.OldList as OldList + +main :: IO () +main = print $ OldList.length (head [['a','b','c']]) + + diff --git a/example/Tuple.hs b/example/Tuple.hs new file mode 100644 --- /dev/null +++ b/example/Tuple.hs @@ -0,0 +1,7 @@ +module Main where + +import Data.Proxy (Proxy(..)) +import Safe.Length (safeLength) + +main :: IO () +main = print $ safeLength (Proxy :: Proxy [Char]) ('a', 'b') diff --git a/safe-length.cabal b/safe-length.cabal new file mode 100644 --- /dev/null +++ b/safe-length.cabal @@ -0,0 +1,36 @@ +name: safe-length +version: 0.1.0.0 +synopsis: Tired of accidentally calling length on tuples? Relief at last! +homepage: http://www.github.com/stepcut/safe-length +license: BSD3 +license-file: LICENSE +author: Jeremy Shaw +maintainer: jeremy@n-heptane.com +category: Data +build-type: Simple +cabal-version: >=1.10 +data-files: + example/BrokenTuple.hs + example/GoodTuple.hs + example/List.hs + example/NestedList.hs + example/OldList.hs + example/Tuple.hs + +library + exposed-modules: Safe.Length + build-depends: base >=4.8 && <4.9 + hs-source-dirs: src + default-language: Haskell2010 + +test-suite tests + type: exitcode-stdio-1.0 + main-is: Main.hs + hs-source-dirs: tests + build-depends: base, + hspec, + hspec-core, + QuickCheck, + safe-length, + should-not-typecheck + default-language: Haskell2010 diff --git a/src/Safe/Length.hs b/src/Safe/Length.hs new file mode 100644 --- /dev/null +++ b/src/Safe/Length.hs @@ -0,0 +1,9 @@ +module Safe.Length where + +import Data.Proxy (Proxy(..)) + +safeLength :: (Foldable f) => Proxy (f a) -> f a -> Int +safeLength _ f = length f + +list :: Proxy [a] +list = Proxy diff --git a/tests/Main.hs b/tests/Main.hs new file mode 100644 --- /dev/null +++ b/tests/Main.hs @@ -0,0 +1,37 @@ +{-# OPTIONS_GHC -fdefer-type-errors #-} +------------------------------------------------------------------------------ +-- | +-- Module : Main +-- Stability : experimental +-- Portability : POSIX +-- +------------------------------------------------------------------------------ +module Main where + +import Data.Proxy (Proxy(..)) +import Safe.Length (safeLength) +import Test.Hspec +import Test.QuickCheck (property) +import Test.ShouldNotTypecheck (shouldNotTypecheck) + +------------------------------------------------------------------------------ +-- | Testing main +main :: IO () +main = hspec spec + +------------------------------------------------------------------------------ +-- | Spec +spec :: Spec +spec = do + describe "safeLength tests" $ + tests + +tests = do + it "length of a tuple is 1" $ + property $ safeLength (Proxy :: Proxy (Char, Char)) ('a', 'b') == 1 + it "Can't accidentally take the length of a tuple when we don't mean to" $ + shouldNotTypecheck (safeLength (Proxy :: Proxy [Char]) ('a', 'b')) + it "Can't accidentally take the length of the wrong level of a nested list" $ + shouldNotTypecheck (safeLength (Proxy :: Proxy [[Char]]) (head [['a', 'b', 'c']] :: [Char])) + it "Can take the length of a list." $ + property $ safeLength (Proxy :: Proxy [Char]) ['a', 'b'] == 2