pretty-error (empty) → 0.1.0.0
raw patch · 4 files changed
+314/−0 lines, 4 filesdep +basedep +basic-preludedep +bytestringsetup-changed
Dependencies added: base, basic-prelude, bytestring, pretty-show
Files
- LICENSE +202/−0
- Setup.hs +2/−0
- pretty-error.cabal +36/−0
- src/PrettyError.hs +74/−0
+ LICENSE view
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+ Setup.hs view
@@ -0,0 +1,2 @@+import Distribution.Simple+main = defaultMain
+ pretty-error.cabal view
@@ -0,0 +1,36 @@+name: pretty-error+version: 0.1.0.0+category: Error Handling+synopsis: Pretty error messages for runtime invariants+description: Sometimes you need to assume something at runtime that you can't prove in the+ type system. When you do that, you should make sure you get a good error+ message if ever your assumption turns out to be wrong. That's what this library+ is for.+ .+ Use the functions in here to get high quality error messages for when your+ invariants don't hold at runtime. The functions all pretty print any Haskell+ values given to them, which makes it easier to understand what's going on when+ your code breaks.+homepage: https://github.com/jml/pretty-error+license: Apache-2.0+license-file: LICENSE+author: Jonathan M. Lange+maintainer: jml@mumak.net+copyright: (c) 2015 Jonathan M. Lange+build-type: Simple+cabal-version: >=1.10++source-repository head+ type: git+ location: git://github.com:jml/pretty-error.git++library+ exposed-modules: PrettyError+ build-depends: base >= 4 && < 5+ , basic-prelude+ , bytestring+ , pretty-show+ hs-source-dirs: src+ default-language: Haskell2010+ default-extensions: NoImplicitPrelude+ , OverloadedStrings
+ src/PrettyError.hs view
@@ -0,0 +1,74 @@+{-| Pretty runtime error messages++These functions can be used to raise clear, understandable error messages for+when your program violates an invariant at runtime.++In particular, 'assertRight' handles a common case where we "know" that a+particular 'Either' is going to be 'Right', and so we want to be able to+unpack the value but also provide a high-quality error message if the value+does somehow turn out to be a 'Left'.++-}++module PrettyError+ ( assertRight+ , fromRight+ , ppText+ , prettyError+ ) where++import BasicPrelude++import Data.ByteString.Char8 (pack)+import Text.Show.Pretty (ppShow)+++-- | Assert that value is 'Right'. Throw error if it's 'Left'.+--+-- The first argument is a message which can be used to explain why this+-- error should not have happened.+--+-- Use 'fromRight' if you don't want to provide a message.+--+-- >>> assertRight "Artificial example" (Right 5)+-- 5+--+-- >>> assertRight "Artificial example" (Left "error message")+-- *** Exception: Artificial example: "error message"+assertRight :: Show a => Text -- ^ A message describing the assertion+ -> Either a b -- ^ The 'Either' to unpack+ -> b -- ^ The unpacked 'Right' value+assertRight _ (Right r) = r+assertRight message (Left e) = terror $ message ++ ": " ++ ppText e+++-- | Extract the value out of a 'Right', or throw an error from a 'Left'+-- made up of the pretty-printed 'Left' value.+--+-- Most of the time you should use 'assertRight', since that allows you to+-- provide a message, which will help to debug the problem.+--+-- >>> fromRight (Right 5)+-- 5+--+-- >>> fromRight (Left 4)+-- *** Exception: 4+fromRight :: Show a => Either a b -> b+fromRight (Left e) = prettyError e+fromRight (Right r) = r+++-- | Pretty print a variable to 'Text'+--+-- Although not strictly related to error messages, this is a handy function+-- to have around if you are using "Text.Show.Pretty" and 'OverloadedStrings'.+ppText :: Show a => a -> Text+ppText = decodeUtf8 . pack . ppShow+++-- | Raise an error with a pretty-printed value.+--+-- >>> prettyError ["foo","bar","baz"]+-- *** Exception: [ "foo" , "bar" , "baz" ]+prettyError :: Show a => a -> b+prettyError = error . ppShow