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{-# LANGUAGE Trustworthy #-}{-# LANGUAGE NoImplicitPrelude #-}------------------------------------------------------------------------------- |-- Module      :  Text.Read-- Copyright   :  (c) The University of Glasgow 2001-- License     :  BSD-style (see the file libraries/base/LICENSE)---- Maintainer  :  libraries@haskell.org-- Stability   :  provisional-- Portability :  non-portable (uses Text.ParserCombinators.ReadP)---- Converting strings to values.---- The "Text.Read" library is the canonical library to import for-- 'Read'-class facilities.  For GHC only, it offers an extended and much-- improved 'Read' class, which constitutes a proposed alternative to the-- Haskell 2010 'Read'.  In particular, writing parsers is easier, and-- the parsers are much more efficient.-------------------------------------------------------------------------------moduleText.Read(-- * The 'Read' classRead(..),ReadS,-- * Haskell 2010 functionsreads,read,readParen,lex,-- * New parsing functionsmoduleText.ParserCombinators.ReadPrec,L.Lexeme(..),lexP,parens,readListDefault,readListPrecDefault,readEither,readMaybe)whereimportGHC.BaseimportGHC.ReadimportData.EitherimportText.ParserCombinators.ReadPasPimportText.ParserCombinators.ReadPrecimportqualifiedText.Read.LexasL-------------------------------------------------------------------------- utility functions-- | equivalent to 'readsPrec' with a precedence of 0.reads::Reada=>ReadSareads=readsPrecminPrec-- | Parse a string using the 'Read' instance.-- Succeeds if there is exactly one valid result.-- A 'Left' value indicates a parse error.---- >>> readEither "123" :: Either String Int-- Right 123---- >>> readEither "hello" :: Either String Int-- Left "Prelude.read: no parse"---- @since 4.6.0.0readEither::Reada=>String->EitherStringareadEithers=case[x|(x,"")<-readPrec_to_Sread'minPrecs]of[x]->Rightx[]->Left"Prelude.read: no parse"_->Left"Prelude.read: ambiguous parse"whereread'=dox<-readPrecliftP.skipSpacesreturnx-- | Parse a string using the 'Read' instance.-- Succeeds if there is exactly one valid result.---- >>> readMaybe "123" :: Maybe Int-- Just 123---- >>> readMaybe "hello" :: Maybe Int-- Nothing---- @since 4.6.0.0readMaybe::Reada=>String->MaybeareadMaybes=casereadEithersofLeft_->NothingRighta->Justa-- | The 'read' function reads input from a string, which must be-- completely consumed by the input process. 'read' fails with an 'error' if the-- parse is unsuccessful, and it is therefore discouraged from being used in-- real applications. Use 'readMaybe' or 'readEither' for safe alternatives.---- >>> read "123" :: Int-- 123---- >>> read "hello" :: Int-- *** Exception: Prelude.read: no parseread::Reada=>String->areads=eithererrorWithoutStackTraceid(readEithers)