Efficient conversion of values into Text https://github.com/RyanGlScott/text-show

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BSD3 licensed by Ryan Scott
Maintained by Ryan Scott

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http://hackage.haskell.org/package/text-show "text-show package on Hackage" [Haskell.org]: http://www.haskell.org "The Haskell Programming Language" [tl;dr Legal: BSD3]: https://tldrlegal.com/license/bsd-3-clause-license-%28revised%29 "BSD 3-Clause License (Revised)"

text-show offers a replacement for the Show typeclass intended for use with Text instead of Strings. This package was created in the spirit of bytestring-show.

At the moment, text-show provides instances for most data types in the array, base, bytestring, and text packages. Therefore, much of the source code for text-show consists of borrowed code from those packages in order to ensure that the behaviors of Show and TextShow coincide.

For most uses, simply importing TextShow will suffice:

module Main where

import TextShow

main :: IO ()
main = printT (Just "Hello, World!")

If you desire it, there are also monomorphic versions of the showb function available in the submodules of Text.Show.Text. See the naming conventions page for more information.

Support for automatically deriving TextShow instances can be found in the TextShow.TH and TextShow.Generic modules.

Changes [2016.11.07]

  • Require criterion-1.1.4 or later. This allows the benchmarks to be run on older versions of GHC.

3.4.1 [2016.10.20]

  • Require QuickCheck-2.9 or later
  • Fix bug in which infix record selectors weren't shown with parentheses


  • The default definitions of showt and showtl were changed to showtPrec 0 and showtlPrec 0, respectively
  • deriveTextShowOptions, deriveTextShow1Options, and deriveTextShow2Options added to TextShow.TH, which allow further configuration of how TextShow(1)(2) instances should be derived using the new Options data type. Options itself contains GenTextMethods, which configures whether manual implementations of TextShow should implement the methods that return strict and lazy Text. * The defaultOptions uses SometimesTextMethods, which only implements the Text-returning methods if the datatype contains only nullary constructors (i.e., it is an enumeration type). For example, deriveTextShow = deriveTextShowOptions defaultOptions. One can also choose AlwaysTextMethods or NeverTextMethods instead.
  • The internals of TextShow.Generic were refactored so that is possible to generically derive showbPrec, showtPrec, and showtlPrec (which use Builder, strict Text, and lazy Text, respectively). Before, only generic derivation of showbPrec was possible, and all other generic functions were defined in terms of showbPrec. The internal class GTextShow was split up into GShowB, GShowT, and GShowTL, depending on what type it returns. As a result, functions like genericShowtPrec might be faster than before if they are showing something like an enumeration type, since they no longer construct an intermediate Builder. On the other hand, they might be slower if they are showing a constructor with many fields, since they will now be appending lots of Texts. If so, make sure to switch to genericShowbPrec and convert the final Builder to Text instead.
  • Added showtParen, showtSpace, showtlParen, showtlSpace, liftShowtPrec, liftShowtPrec2, liftShowtlPrec, and liftShowtlPrec2 to TextShow
  • Added showtPrecToShowbPrec, showtlPrecToShowbPrec, showtToShowb, showtlToShowb, showbPrecToShowtPrec, showbPrecToShowtlPrec, showbToShowt, and showbToShowtl to TextShow
  • Added showtListWith and showtlListWith to TextShow.Data.List
  • Added Data instance for ConType in TextShow.Generic
  • Require generic-deriving-1.11 or later


  • Refactored the internals of TextShow.Generic to avoid the use of proxies.
  • Made benchmark suite more comprehensive, including benchmarks for showing an enumeration type
  • Microoptimization in derived TextShow1/2 instances involving TextShow.TH
  • Allow building with QuickCheck-2.9
  • Fix GHC HEAD build


  • Added benchmarks


  • Fixed compilation on GHC 8.0


  • Rewrote TextShow.Generic to enable more code reuse. The GTextShow1 and GTextShow1Con classes were eliminated, and GTextShow and GTextShowCon were redesigned to be able to generically implement both showbPrec and liftShowbPrec. The latter two classes now take an additional arity type parameter which is Zero if TextShow is being derived and One is TextShow1 is being derived.


  • Made the derived TextShow output of record datatypes match that of Show in GHC 8.0 (now that Trac #2530 has been reverted)
  • Fixed GHC 8.0 build (again)


  • Added the TextShow.GHC.Stack module, which provides TextShow instances for CallStack and SrcLoc on base-4.8.1 and up.
  • Fix Haddock rendering error


  • GHC 8.0 support
  • The functions showt, showtl, showtPrec, showtlPrec, showtList, and showtlList are now part of the TextShow class. This was done to allow overriding their definitions with more efficient versions specifically for strict or lazy Text. (Currently, no TextShow instance in the text-show package does this, but this may change in the future.)
  • Added the TextShow.Data.Functor.Compose, TextShow.Data.Functor.Product, TextShow.Data.Functor.Sum, and TextShow.Data.Semigroup modules
  • Added TextShow instance for TypeError in TextShow.Control.Exception (GHC 8.0+)
  • Added TextShow instances for TrName and Module in TextShow.Data.Typeable (GHC 8.0+)
  • Added Lift instances for the datatypes in TextShow and TextShow.Generic
  • Renamed the class methods of TextShow1 and TextShow2 to be consistent with the naming conventions of transformers-0.5. They following were renamed: showbPrecWithliftShowbPrec showbPrecWith2liftShowbPrec2 makeShowbPrecWithmakeLiftShowbPrec makeShowbPrecWith2makeLiftShowbPrec2 * genericShowbPrecWithgenericLiftShowbPrec

    In addition, many other monomorphic functions from the various TextShow submodules were also renamed to be consistent with the new lift- prefix.

  • showsToShowb and showbToShows now only convert functions that ignore precedence (i.e., of type a -> ShowS or a -> Builder). Their former role has been given to the new functions showsPrecToShowbPrec and showbPrecToShowsPrec
  • Added FromStringShow1, FromTextShow1, FromStringShow2, and FromTextShow2, which allow defining string Show1/Show2 instances in terms of TextShow1/TextShow2 instances, and vice versa. Be aware that many of these instances cannot be provided if you are using tranformers-0.4, since its version of Data.Functor.Classes uses a very differenltly designed Show1 typeclass (and does not have Show2 at all).
  • Rewrote TextShow.TH's type inferencer. This avoids a nasty GHC 7.8 bug, and it allows TextShow(1)(2) to be derived for more datatypes that can only be expressed with -XTypeInType enabled.
  • Reworked internals of TextShow.Generic. Empty datatypes can now be have generic TextShow and TextShow1 instances.


  • Fixed GHC 7.10.3 build
  • Extended TextShow.Generic to allow genericShowbPrec (and friends) to be used on Generic datatypes with Char#, Double#, Float#, Int#, and Word# argument types, just like string Show does
  • Added Generic1 instances for FromStringShow and FromTextShow
  • Added TextShow instances for UChar, UDouble, UFloat, UInt, and UWord in TextShow.GHC.Generics


  • Restore support for semigroups-0.16.1


  • Require semigroups >= 0.17
  • Added showsToShowb and showbToShows to TextShow
  • Added TextShow1 FromStringShow instance
  • Added showbGiveGCStats, showbDoCostCentres, showbDoHeapProfile, and showbDoTrace to TextShow.GHC.RTS.Flags if using base-4.8.2 or later
  • Exported showbDownPrecWith on earlier versions of GHC
  • Fixed mistakes in TH error output
  • Make Proxy, Coercion, and (:~:) instances poly-kinded
  • Changed implementation of showbByteStringStrict, showbByteStrictLazy(Prec), showbShortByteString (in TextShow.Data.ByteString), showbThreadIdPrec (in TextShow.Control.Concurrent), showbEvent, and showbFdKeyPrec (in TextShow.GHC.Event) to avoid using Strings as an intermediary


  • Changed the top-level module name from Text.Show.Text to TextShow, since the former was extremely verbose without much benefit. As a result, this will break all existing code that depends on text-show.
  • Several typeclasses and functions were renamed so as to not to clash with the Prelude: ShowTextShow Show1TextShow1 Show2TextShow2 showshowt showLazyshowtl showPrecshowtPrec showPrecLazyshowtlPrec showListshowtList showListLazyshowtlList printprintT printLazyprintTL hPrinthPrintT hPrintLazyhPrintTL GShowGTextShow GShow1GTextShow1 genericShowgenericShowt genericShowLazygenericShowtl genericShowPrecgenericShowtPrec genericShowPrecLazygenericShowtlPrec genericShowListgenericShowtList genericShowListLazygenericShowtlList genericPrintgenericPrintT genericPrintLazygenericPrintTL genericHPrintgenericHPrintT genericHPrintLazygenericHPrintTL deriveShowderiveTextShow deriveShow1deriveTextShow1 deriveShow2deriveTextShow2 mkShowmakeShowt mkShowLazymakeShowtl mkShowPrecmakeShowtPrec mkShowPrecLazymakeShowtlPrec mkShowListmakeShowtList mkShowListLazymakeShowtlList mkShowbmakeShowb mkShowbPrecmakeShowbPrec mkShowbListmakeShowbList mkPrintmakePrintT mkPrintLazymakePrintTL mkHPrintmakeHPrintT mkHPrintLazymakeHPrintTL mkShowbPrecWithmakeShowbPrecWith mkShowbPrec1makeShowbPrec1 mkShowbPrecWith2makeShowbPrecWith2 mkShowbPrec2makeShowbPrec2 tracetracet traceLazytracetl traceIdtracetId traceIdLazytracetlId traceShowtraceTextShow traceShowIdtraceTextShowId traceStacktracetStack traceStackLazytracetlStack traceIOtracetIO traceIOLazytracetlIO traceMtracetM traceMLazytracetlM traceShowMtraceTextShowM traceEventtracetEvent traceEventLazytracetlEvent traceEventIOtravetEventIO traceEventIOLazytracetlEventIO traceMarkertracetMarker traceMarkerLazytracetlMarker traceMarkerIOtracetMarkerIO traceMarkerIOLazytracetlMarkerIO genericTraceShowgenericTraceTextShow genericTraceShowIdgenericTraceTextShowId genericTraceShowMgenericTraceTextShowM mkTraceShowmakeTraceTextShow mkTraceShowIdmakeTraceTextShowId mkTraceShowMmakeTraceTextShowM
  • Added TextShow Lifetime instance in TextShow.GHC.Event (if using base- or later)
  • Generalized tracetM, tracetlM, and traceTextShowM to use an Applicative constraint instead of Monad
  • Fixed a bug in which the TextShow(1) instances for Proxy, (:~:), and Coercion didn't use -XPolyKinds
  • Fixed a bug in the Template Haskell deriver which would cause deriveTextShow to fail on type parameters with sufficiently high kinds


  • The Show1 class has been completely overhauled. Show1 now uses the function showbPrecWith, which takes as an argument a function of type Int -> a -> Builder to show occurrences of the type parameter (instead of requiring the type parameter to be a Show instance). This matches the new implementation of Show1 in the next version of transformers. A similar Show2 class (with the function showbPrecWith2) was also added.
  • As a consequence, Show1 instances should no longer be defined in terms of showbPrec; rather, Show instances should be defined in terms of showbPrecWith or showbPrecWith2, and Show1 instances can be defined in terms of showbPrecWith2.
  • The showbPrec1 function is no longer a class method of Show1, but is now a standalone function defined in terms of showbPrecWith. showbPrec1 can be useful for defining Show instances. A similar showbPrec2 function was also added.
  • The monomorphic functions in the many submodules of this package have been generalized (where possible) to use Show1 and Show2 instances. These functions have -PrecWith and -PrecWith2 suffixes, respectively.
  • Because of the generality of the new showPrecWith function, Show1 instances are now possible for Ratio, Alt, Rec1, M1, (:+:), (:*:), and (:.:).
  • Removed many silly instances for FromStringShow and FromTextShow, since they'll never be used in the ways suggested by those instances to begin with.
  • The Template Haskell engine has been completely overhauled. Deriving Show1 and Show2 instances are now possible using the deriveShow1 and deriveShow2 functions. See the documentation in Text.Show.Text.TH for more details. In addition, the mkShowbPrecWith, mkShowbPrec1, mkShowbPrecWith2, and mkShowbPrec2 functions were added.
  • Removed the ability to call deriveShow or mkShowbPrec (or other functions prefixed with mk-) using a data family name. This is considered a misfeature. If you want to derive Show for data family instances, use the corresponding data instance or newtype instance constructor name as an argument instead.
  • Removed PragmaOptions, deriveShowPragmas, defaultInlineShowbPrec, defaultInlineShowb, and defaultInlineShowbList, as it was impossible to make Template Haskell-generated pragmas work consistently across different versions of GHC. If you really want to use INLINE and SPECIALIZE instance pragmas with your Template Haskell-generated code, create manual instances with mkShowbPrec and family.
  • Show1 instances can now be created generically using the genericShowbPrecWith function in Text.Show.Text.Generics. A genericShowbPrec1 was also added.
  • Added generic-deriving as a dependency, which allows generics-related code to be exported on more versions of GHC
  • ConType (in Text.Show.Text.Generics) now has an Inf String constructor instead of Inf Builder. As a result, ConType now always an Eq and Ord instance, and a Read ConType instance was added.
  • Typeable instances for the promoted data constructors 'FromStringShow and 'FromTextShow
  • Added showbFPFormat to Text.Show.Text.Data.Floating
  • Revamped test suite

  • Retroactive CHANGELOG update


  • Fix test suite build with older versions of QuickCheck


  • Exported formatRealFloatB and formatRealFloatAltB from Text.Show.Text.Data.Floating. Reexported FPFormat (from text) in the same module, and added a Text Show instance for it.
  • The Show instance for Ratio a now only requires a Show a constraint if using base- or later (if using base-, it requires a (Show a, Integral a) constraint)
  • Added showbSingPrec to Text.Show.Text.GHC.TypeLits (if using base-4.6)
  • Modules which were previously exported only if using a recent-enough version of GHC/base (e.g., Text.Show.Text.GHC.Generics) are now always exposed. If the functionality that the module provides is not available on a given version of GHC/base, the module will not expose anything.
  • Bump lower version bounds of text to 0.11.1 due to reexporting FPFormat
  • Added showbUnicodeException, showbI16Prec, showbDecodingPrec, and showbSizePrec functions (and corresponding Show instances) to Text.Show.Text.Data.Text
  • Made GShow in Text.Show.Text.Generics poly-kinded
  • The Template Haskell deriver (and GShow) now handles "infix" data constructors that are applied as prefix correctly (e.g., data Amp a = (:&) a a)
  • The Template Haskell deriver now handles showable unlifted types (Char#, Double#, Float#, Int#, and Word#) correctly on GHC 7.11 and later
  • The Template Haskell derive now does not parenthesize record types regardless of precedence on GHC 7.11 and later
  • Fixed build on GHC 7.2
  • Changed test-suite to use hspec, which allows for it to be built on GHC 7.0 and 7.2

  • Disabled print-related tests, as they sporadically break referential transparency for unknown reasons
  • Fixed build on Windows


  • Added showbConstPrec (and corresponding Show and Show1 instances for Const) to Text.Show.Text.Control.Applicative
  • Added showbUArrayPrec (and corresponding Show instance for UArrays) and showbIArrayPrec to Text.Data.Text.Data.Array.
  • Renamed showbListDefault to showbListWith to match how Text.Show names it
  • Exposed showbShortByteString with all versions of bytestring by using the bytestring-builder package
  • Corrected the Show instance for Lexeme (in Text.Show.Text.Text.Read.Lex)
  • Fixed TypeRep output on GHC 7.10 and later
  • Removed LitChar and LitString from Text.Show.Text.Data.Char, as they were not as useful as I had imagined.
  • Removed the deprecated replicateB function
  • Typable instances for Show, Show1, and GShow (with GHC 7.8 and later)
  • Typeable instance for ConType
  • Only derive Eq and Ord for ConType if a recent-enough version of text is used
  • Changed the implementations of some functions in Text.Show.Text.Debug.Trace to use ByteStrings instead of Strings

  • Forgot to include some header files in text-show.cabal


  • deriveShow can now construct instances for data families, using either the data family name or a data instance constructor as an argument. See the documentation in Text.Show.Text.TH for more details.
  • Fixed a bug in which infix backticked data constructors (e.g., `data Add = Int `Plus` Int`) would not be shown correctly.
  • Fixed typo in Text.Show.Text.GHC.RTS.Flags
  • Removed the phantom-type detecting mechanism with template-haskell- or higher. This method of finding phantom types is intrinsically flawed and is not usable on older GHCs.
  • Added generics support with the Text.Show.Text.Generic and Text.Show.Text.Debug.Trace.Generic modules
  • Deprecated replicateB in favor of timesN from the semigroups library
  • Added FromTextShow to Text.Show.Text, which admits a String Show instance for any data type with a Text Show instance (the counterpart of FromStringShow)
  • Added Monoid and Semigroup instances for FromStringShow, Semigroup instance for LitString, IsChar instance for LitChar, and IsString instance for [LitChar]
  • Changed the String Show instances of FromStringShow, LitChar, and LitString to more closely match the Text Show instances. As a result, the Read instances for these data types were also changed so that read . show = read . show = id.
  • Removed the recent-text flag. We'll allow users to build with older versions of text, but the latest version is recommended. Because of this, the integer-simple and integer-gmp flags are not needed.
  • Removed the integer-gmp2 flag, as it supported a configuration that didn't actually compile on GHC
  • Removed the transformers-four flag, as it is not needed now that transformers-compat is a dependency


  • Fix build for GHC 7.10, old GHC versions, and Windows
  • Removed the Text.Show.Text.Data.Containers and Text.Show.Text.Data.Time modules. The modules for the data types in containers and time were migrated to a separate library, text-show-instances.
  • Removed the -ftext-format flag, as text-show no longer uses text-format.
  • A serious bug in the text package that caused segfaults when building large Integers was fixed in text- A flag (-frecent-text) was added that allows you to take advantage of this.
  • Fixed a bug that would cause the output of functions in the Text.Show.Text.Data.Floating module to not match base depending on what version of base is used.
  • The type signatures of lambda expressions generated by mkShow and related functions were loosened to allow them to be used to "manually" derive Show instances for data types with higher-kinded type parameters or type arguments with restricted Show instances. This should not be a breaking change; you can simply do more with mkShow et al. than you could before. For more information, see the documentation in Text.Show.Text.TH.
  • Loosened the Show instance of Complex a to only depend on Show a (previously required RealFloat a) if using base- or later
  • Moved showbRatioPrec to Text.Show.Text.Data.Ratio, showbComplexPrec to Text.Show.Text.Data.Complex, showbProxy to Text.Show.Text.Data.Proxy, and showbFingerprint to Text.Show.Text.GHC.Fingerprint
  • Added deriveShowPragmas to Text.Show.Text.TH to allow users to specify INLINE or SPECIALIZE instance pragmas with Show instances.
  • Added FromStringShow, showbSpace, showbUnary, showbUnary1, and showbBinary1 to Text.Show.Text
  • Added mkShowList, mkShowListLazy, and mkShowbList to Text.Data.Text.TH
  • For base- and above, added the Text.Show.Text.Data.Functor.Identity, Text.Show.Text.Data.Void, Text.Show.Text.GHC.RTS.Flags, Text.Show.Text.GHC.StaticPtr, and Text.Show.Text.Numeric.Natural modules. Also added Show instances for AllocationLimitExceeded in Text.Show.Text.Control.Exception and Alt in Text.Show.Text.Data.Monoid. Also fixed the Show instance for Fixed values.
  • Added the Text.Show.Text.Data.GHC.Conc.Windows module (Windows-only)
  • Added the Text.Show.Text.Data.OldTypeable module for base-4.7
  • Added the Text.Show.Text.GHC.TypeLits module for base-4.6 and above
  • Added the Text.Show.Text.Debug.Trace and Text.Show.Text.Debug.Trace.TH modules as an analog to Debug.Trace
  • Added the Show1 class and corresponding instances for unary type constructors.
  • Added LitChar and LitString to Text.Show.Text.Data.Char
  • Exported asciiTabB in Text.Show.Text.Data.Char
  • Renamed showbTextStrict to 'showbText' (to keep with naming conventions in the text library) and added showbBuilder to Text.Show.Text.Data.Text.


  • Added the utility functions toText and toString for working with Builders.


  • Due to GHC bug #5289, projects that depend on the double-conversion library (such as text-format, a dependency of text-show) may break due to GHC incorrectly linking against libstdc++. Therefore, text-show was changed so that it does not depend on text-format by default. This behavior can be changed by using the -ftext-format flag when using cabal.
  • Added showbZonedTime to Text.Show.Text.Data.Time (and corresponding Show instance for ZonedTime)
  • Exposed showbMaskingState (is was already there, I just forgot to export it)
  • If using GHC 7.6 or earlier, depend on tagged so that Data.Proxy (and thus showbProxy from Text.Show.Text.Data.Typeable) can be used
  • Refactored code to use Template Haskell derivations when possible

  • Added showList and showListLazy
  • Don't use showbListDefault to show containers data types
  • Added the ability to splice show functions for arbitrary data types (even if they aren't Show instances). These functions are mkShow, mkShowLazy, mkShowPrec, mkShowPrecLazy, mkShowb, mkShowbPrec, mkPrint, mkPrintLazy, mkHPrint, and mkHPrintLazy.

  • Lots of bugfixes
  • Show instances for many other data types in base, containers and time
  • Exposed internal modules with monomorphic functions
  • Text.Show.Text now exports Data.Text.Lazy.Builder for convenience
  • Add showLazy, showPrec, showPrecLazy, printLazy, hPrint, hPrintLazy, lengthB, and replicateB
  • Template Haskell derivation of Show instances (doesn't support data families yet)

  • Added Show instances for strict and lazy Text

  • Initial commit
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