{- | Module: Text.Sayable This module provides a set of data structures, classes, and operators that facilitate the construction of a Prettyprinter Doc object. = Motivation Standard prettyprinting is a monotonic conversion that does not allow for customization for different uses or environments. For example, when debugging, full and explicit information about a structure should be generated, but for checkpoint logging, a simple overview is usually more appropriate. This library provides for an additional type parameter that can be used to control the conversion to a suitably verbose Prettyprinter Doc representation. This is also highly useful in conjunction with logging to generate successively more verbose information as the logging verbosity increases. = Usage Typical usage is to create a sayable message using the operators defined here and then extract Prettyprinter Doc from the saying and convert it to a printable format (here, simply using @show@ for the default Prettyprinter rendering). @ import qualified Prettyprinter as PP foo :: Members '[ Logging SayMessage, Config ] r -> a -> b -> Eff r [b] foo arg1 arg2 = do putStrLn $ show $ saying $ sayable @info "Entering foo with" &- arg1 &- "and" &- arg2 rslt <- something arg1 arg2 case rslt of Right vals -> do putStrLn $ show $ saying $ sayable @"verbose" $ "Foo successfully returning" &% length vals &- "results:" &- vals return vals Left err -> do putStrLn $ show $ saying $ sayable @"error" $ "Foo error (" &- arg1 &- PP.comma &- arg2 &- ") is" &- err throwError err @ [Note: if viewing via Haddock HTML, the '@' in front of @"info"@, @"verbose"@, and @"error"@ on the putStrLn lines above may not be visible.] There are three messages printed: one on entry and one on either the success or failure paths. Each message may have different levels of information reported for the various arguments. == The @saytag@ type parameter Each sayable message uses a @TypeApplication@ to specify a "saytag" which should be used for controlling the rendering of that message (e.g. "info", "verbose", "error", etc.). As a developer, it is encouraged to use whatever saytag makes sense relative to the current context and type of information being processed. == Individual Arguments The arguments passed to the sayable should be instances of the 'Sayable' class. There are a number of standard instances of 'Sayable', but an instance can be declared for any object that might be output. The 'Sayable' class has two class parameters: the second is object to be converted, and the first is the "saytag". This allows different Sayable instances for an object to be used in different saytag scenarios. For example: @ import Network.URL instance Sayable "verbose" URL where sayable url = let newline = PP.line :: PP.Doc SayableAnn prettyShow x = PP.viaShow x :: PP.Doc SayableAnn in "URL {" &- "url_type=" &- prettyShow (url_type url) &- newline &- "url_path=" &- url_path url &- newline &- "url_params=" &* url_params url &- "}" instance Sayable saytag URL where sayable = Sayable . PP.viaShow . exportURL @ The above would cause a url emitted via a "verbose" saytag to be expanded into a report on each individual field, whereas all other saytags would simply output the @exportURL@ representation of the @URL@. >>> let host = Host (HTTP True) "github.com" Nothing >>> url' = URL (Absolute host) "by/one" >>> saying $ sayable @"verbose" url' URL { url_type= Absolute (Host {protocol = HTTP True, host= "github.com", port= Nothing}) url_path= by/one url_params= } >>> saying @"info" $ sayable url' https://github.com:442/by/one There are some tricky elements to the above however; see "Unfortunate Details" below. Note that there are several pre-declared Sayable instances for common datatypes for convenience. == Operators In the logging lines above, there are three operators used, each of which starts with the @&@ character: ['&-'] This is the standard operator that takes two Sayable arguments and converts them to their Sayable form, then combining them (with an intervening space). This is the standard argument to use for building the output message from distinct parts. ['&+'] This is a variation of the standard '&-' operator that has no intervening space between the two arguments that are converted to a Sayable form. ['&%'] This is a variation of the standard '&-' operator that only requires the second argument to be an instances of Prettyprinter.Pretty instead of an instance of 'Sayable', which can be convenient and avoids the need to define large numbers of 'Sayable' instances. ['&*'] This is a helper operator whose second argument is a 'Foldable' series of 'Sayable' elements. This will fold over the series, adding the 'Sayable' instance value for each element separated by commas. ['&+*'] This is similar to the '&*' helper, but it uses the first argument as the separator between the elements of the 'Foldable' second argument (instead of the ", " default used by the '&*' helper). ['&?'] This is a helper operator whose second argument is a @Maybe a@ (where @a@ is a @Showable@). This will emit the @Showable@ of @a@ if the argument is a 'Just' value, or nothing (an empty Text Showable) if the argument is a 'Nothing' value. ['&<'] This is a helper operator that generates a newline between its two arguments. ['&<*'] This is a helper operator that combines the '&<' and '&*' operators: it generates a newline between its two arguments and the second argument is a Foldable that will be output separated by commas. ['& PrettyPrinter.Doc ann@ function) to the foldable collection represented by the second argument. ['&!$*'] This helper operator is a combination of the '&!' operator and the '&*' operator: it applies the first argument (a @PrettyPrinter.Doc ann -> PrettyPrinter.Doc ann@ function) to the *result* of a foldable collection represented by the second argument. It is similar to the '&!*' operator except that it applies the Prettyprinter conversion to the singular result of the list rather than to the list of results. ['&!+*'] This helper operator is a combination of the '&!' operator and the '&+*' operator (and is a trinary rather than a binary operator): it applies the first argument (a @[PrettyPrinter.Doc ann] -> PrettyPrinter.Doc ann@ function) to the foldable collection represented by the third argument, using the second argument to specify the separators between the elements. == Convenience/other * This module also provides an instance to convert a Sayable back into a Prettyprinter.Pretty. * This module provides a helper function: 't'' which can be useful when @OverloadedStrings@ is active to designate its argument as being a Text string. If the following: @ saying @"error" $ "This is an error:" &- err @ results in an error @Could not deduce (Data.String.IsString m0) arising from the literal '"This is an error:"'@ then this helper can fix that: @ saying @"error" $ t'"This is an error:" &- err @ * This module provides a helper function: 'd'' which can be useful when creating a PP.Doc SayableAnn for inclusion into a 'Sayable' by fixing the @ann@ of 'PP.Doc ann' to 'SayableAnn'. Fixes the error: @ • Overlapping instances for Sayable saytag (PP.Doc ann1) arising from a use of ‘&-’ Matching instances: instance [overlappable] Sayable tag (PP.Doc ann) -- Defined in ‘Taphos.Say’ instance Sayable tag (PP.Doc SayableAnn) -- Defined in ‘Taphos.Say’ (The choice depends on the instantiation of ‘saytag, ann1’ To pick the first instance above, use IncoherentInstances when compiling the other instance declarations) @ This is similar to the '&%' operator except it takes a single argument rather than the two arguments passed to the operator. * The pattern of converting a saying into a String (e.g. for passing to putStrLn) is fairly common, so the simplistic operations of that is provided by the 'sez' function. == Generating final output The 'sayable' method of the 'Sayable' class generates instances of the 'Saying' data object. The 'saying' function can be used to extract the 'Prettyprinter.Doc' from the 'Saying' object. This Doc can then be converted to a 'Lumberjack.LogMessage' or to a plain Text format for display. == Unfortunate Details The use of the Sayable class to translate individual objects is fairly straightforward, but the management of the phantom @saytag@ type parameter is a bit tricky. As described above (with the Network.URL example), it's possible to provide different output generation by providing specialized instances for specific saytags. The determination of which instance GHC will use has some idiosyncrasies that make lead to unexpected instance selection when used transitively (viz. https://ghc.gitlab.haskell.org/ghc/doc/users_guide/extsinstances.html). For instance: @ import Network.URL ( URL ) newtype Foo = Foo URL data Bar a = Bar String a -- [previous instances for Sayable URL here...] instance Sayable "loud" Foo where sayable (Foo url) = t'"{!" &- url &- t'"!}" instance Sayable saytag Foo where sayable (Foo url) = sayable url instance (Sayable saytag a) => Sayable saytag (Bar a) where sayable (Bar b a) = b &- t'"is" &- a let host = Host (HTTP True) "github.com" Nothing let url' = URL (Absolute host) "by/one" let foo = Foo url' let bar = Bar "bar" foo @ will generate: >>> putStrLn $ sez @"info" $ t'"INFO:" &- bar &- "via" &- foo INFO: bar is "https://github.com/by/one" via "https://github.com/by/one" >>> putStrLn $ sez @"loud" $ t'"LOUD:" &- bar &- "via" &- foo LOUD: bar is {! "https://github.com/by/one" !} via {! "https://github.com/by/one" !} which is expected. However, if the calls to 'sez' are moved to a separate file from the instance declarations, the compilation error will be: @Overlapping instances for Sayable "loud" Foo arising from a use of &-@ for the last (loud) line. To resolve this, use OVERLAPPING and/or OVERLAPPABLE specifications on the instance declarations. Usually it's sufficient (and easiest) to add the OVERLAPPABLE to the generic instance: > instance Sayable "loud" Foo where sayable (Foo s) = t'"{!" &- s &- t'"!}" > instance {-# OVERLAPPABLE #-} Sayable saytag Foo where sayable (Foo s) = sayable s [Note: if you are viewing the above via Haddock HTML, the second line has the @instance@ keyword, followed by an open comment directive (open curly brace, dash, hash) , @OVERLAPPABLE@ and a closing comment directive (hash, dash, close curly brace), followed by the @Sayable@ keyword, but that doesn't render under HTML Haddock (circa 2022).] There's another twist to this story though. To observe this new twist, add a @Baz@ datastructure and its generic 'Sayable' instance: > data Baz = Baz Foo > instance Sayable saytag Baz where sayable (Baz a) = t'"BAZ :=" &- foo Now the following calls and corresponding output can be observed: >>> putStrLn $ sez @"info" $ t'"INFO:" &- bar &- t'"and" &- baz INFO: bar is "https://github.com/by/one" and BAZ := "https://github.com/by/one" >>> putStrLn $ sez @"loud" $ t'"LOUD:" &- bar &- t'"and" &- baz LOUD: bar is {! "https://github.com/by/one" !} and BAZ := "https://github.com/by/one" Notice how the @foo@ value in @bar@ changes when the '@"loud"' saytag is used, but the same @foo@ value in @baz@ does not change! The difference here is in the mechanism GHC uses to select instances (as described on the referenced link above). In short, for @bar@, the generic 'Sayable' instance has a constraint for the inner element, which causes GHC to wait until the final use case to determine what the specific type parameters are; it sees the @"loud"@ @saytag@ value and selects the @"loud"@ @Foo@ 'Sayable' instance as the most specific. However, the @baz@ 'Sayable' instance does not have a constraint, so GHC takes the conservative approach and uses the most general instance, which means that it transitively selects the generic @Foo@ 'Sayable' instance instead of the @"loud"@ instance. There are two ways to fix this: 1. Provide explicit @"loud"@ 'Sayable' instance for @Baz@. This is problematic, because this must be done for *each* saytag for which there is a variation and it must be done for *each* upper level 'Sayable' instance. 2. Provide 'Sayable' constraints for each sub-element. This generates larger type signatures, but is preferrable to solution 1 because it makes no assumptions about current or future saytags and variations. This 'Sayable' constraint was already present on the @Bar@ 'Sayable' instance because of the parameterized type for @Bar@; the @Baz@ type has no type parameter, but a constraint can still be added for each interior type: > instance Sayable saytag Foo => Sayable saytag Baz where > sayable (Baz a) = t'"BAZ :=" &- foo Using either of the above solutions, the new output is fully specialized as desired: >>> putStrLn $ sez @"info" $ t'"INFO:" &- bar &- t'"and" &- baz INFO: bar is "https://github.com/by/one" and BAZ := "https://github.com/by/one" >>> putStrLn $ sez @"loud" $ t'"LOUD:" &- bar &- t'"and" &- baz LOUD: bar is {! "https://github.com/by/one" !} and BAZ := {! "https://github.com/by/one" !} The good news here is that the complexity is all handled at the Sayable instance definition and the client usage calls are all unaffected, regardless of which solution is chosen. -} {-# LANGUAGE AllowAmbiguousTypes #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE DefaultSignatures #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE LambdaCase #-} {-# LANGUAGE MagicHash #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} {-# OPTIONS_GHC -fno-warn-orphans #-} module Text.Sayable ( -- * Primary Class Sayable(sayable) -- * Result Datatype , Saying(Saying, saying) -- * Helper operators -- -- | These are typically used to facilitate the expression of a sayable -- phrase containing multiple elements. , t' , d' , (&-) , (&+) , (&%) , (&*) , (&+*) , (&?) , (&<) , (&<*) , (&) ) import qualified Prettyprinter as PP -- | The main class of things that can be passed to 'sayable'. Arguments -- provided to 'sayable' or 'sez' will be converted to the sayable form by -- automatically applying the appropriate instance of this class. The -- default implementation is: -- -- > sayable = Saying . Prettyprinter.pretty class Sayable (tag :: Symbol) v where sayable :: v -> Saying tag default sayable :: PP.Pretty v => v -> Saying tag sayable = Saying . PP.pretty -- | The result of applying the sayable method of the Sayable class is -- the Saying object. This object is internal to the Say module and -- is mostly used for subsequently combining with additional Saying -- objects to produce the final Saying object that is converted to a -- SayMessage for actual logging. A Sayable supports a Semigroup -- combinator to allow composition of messages. newtype Saying (tag :: Symbol) = Saying { saying :: PP.Doc SayableAnn } instance Semigroup (Saying tag) where Saying sm1 <> Saying sm2 = Saying $ sm1 <+> sm2 -- | Inputs that are 'Sayable', i.e. that can be converted to a Saying instance {-# OVERLAPPING #-} (tagA ~ tagB) => Sayable tagA (Saying tagB) where sayable = id instance Sayable tag Text instance Sayable tag String instance Sayable tag Char instance Sayable tag Bool instance Sayable tag Int instance Sayable tag Integer instance Sayable tag I.Int32 instance Sayable tag I.Int64 instance Sayable tag W.Word8 instance Sayable tag W.Word16 instance Sayable tag W.Word32 instance Sayable tag W.Word64 instance Sayable tag Natural instance Sayable tag TL.Text instance Sayable tag BS.ByteString where sayable = sayable . TE.decodeUtf8 instance Sayable tag BSL.ByteString where sayable = sayable . TEL.decodeUtf8 instance Sayable tag X.SomeException where sayable = sayable . X.displayException instance Sayable tag (PP.Doc SayableAnn) where sayable = Saying instance {-# OVERLAPPABLE #-} Sayable tag (PP.Doc ann) where sayable = Saying . PP.unAnnotate -- | A Saying can be converted back into a PP.Pretty instance -- representation. Just saying... :-) -- -- This can be convenient to apply Prettyprinter formatting elements. -- For example: -- -- > instance Sayable saytag Foo where -- > sayable foo = sayable @saytag $ Prettyprinter.group $ Prettyprinter.pretty -- > $ field1 foo &- sayable @saytag PP.line &- field2 foo -- -- This uses 'Prettyprinter.group' and 'Prettyprinter.line' formatters to show -- the two fields on the same line if they will fit, otherwise stacked on top of -- each other. Note that the second portion needs an explicit @TypeApplication@ -- (applied here to the 'Prettyprinter.line') because the 'Prettyprinter.group' -- and 'Prettyprinter.pretty' functions do not propagate that outer @saytag@ to -- the inner portion. instance PP.Pretty (Saying tag) where pretty = PP.unAnnotate . saying -- | A helper operator allowing two Sayable items to be composed into -- a Saying. This is the most common operator used to construct -- composite Sayable messages. The two Sayable items are separated by -- a space. (&-) :: forall saytag m n . (Sayable saytag m, Sayable saytag n) => m -> n -> Saying saytag m &- n = sayable m <> sayable n infixl 1 &- -- | A helper operator allowing two Sayable items to be composed into -- a Saying by placing the two Sayable items immediately adjacent with -- no intervening spaces. This is the high-density version of the -- more common '&-' operator. (&+) :: forall saytag m n . (Sayable saytag m, Sayable saytag n) => m -> n -> Saying saytag m &+ n = Saying $ (saying $ sayable @saytag m) <> (saying $ sayable @saytag n) infixl 1 &+ -- | A helper operator allowing a Sayable item to be composed with a -- Pretty item into a Saying. This is infrequently used and primarily -- allows the composition of a data object which has a "Prettyprinter" -- instance but no 'Sayable' instance. (&%) :: (Sayable tag m, PP.Pretty n) => m -> n -> Saying tag m &% n = sayable m <> sayable (PP.pretty n :: PP.Doc SayableAnn) infixl 1 &% -- | A helper operator to /apply/ a "Prettyprinter" (@Doc ann -> Doc -- ann@) function (the first argument) to the Sayable in the second -- argument. This is different from the '&%' operator in that the -- former uses 'Prettyprinter.hsep' to join two independent -- 'Prettyprinter.Doc' 'Saying' values, whereas this operator applies -- a transformation (e.g. @Prettyprinter.annotate AnnValue@ or -- @Prettyprinter.align . Prettyprinter.group@) to the -- 'Prettyprinter.Doc' in the second 'Saying' argument. (&!) :: forall tag m . Sayable tag m => (PP.Doc SayableAnn -> PP.Doc SayableAnn) -> m -> Saying tag pf &! m = Saying $ pf $ saying $ sayable @tag m infixl 2 &! -- | A helper operator allowing a Sayable item to be composed with a -- Foldable series of Sayable items. This can be used when the second -- argument is a List, Sequence, Set, etc. to add all elements of the -- set (comma-separated). -- -- Note: this instance makes it easy to output lists, Sequence, -- NonEmpty.List, etc., but it can have undesireable effects for data -- structures whose Foldable (Functor) is irregular... for example, -- folding over a tuple only returns the 'snd' value of a tuple. -- Consider wrapping tuples in a newtype with an explicit Sayable to -- avoid this. (&*) :: forall tag m e t . (Sayable tag m, Sayable tag e, Foldable t) => m -> t e -> Saying tag m &* l = let addElem e (s, Saying p) = ("," <> PP.softline, Saying $ saying (sayable @tag e) <> s <> p) in sayable m <> (snd $ foldr addElem ("", Saying PP.emptyDoc) l) infixl 1 &* -- | A helper operator that generates a sayable from a list of sayable -- items, separated by the first sayable (&+*) :: forall tag m e t . (Sayable tag m, Sayable tag e, Foldable t) => m -> t e -> Saying tag m &+* l = let addElem e (s, Saying p) = (Just m, case s of Nothing -> sayable @tag e &+ p Just s' -> sayable @tag e &+ s' &+ p ) in snd $ foldr addElem (Nothing, Saying PP.emptyDoc) l infixl 2 &+* -- | A helper operator that applies the first argument which converts an array of -- 'Prettyprinter.Doc ann' elements to a single 'PrettyPrinter.Doc ann' element -- to the second argument, which is a Foldable collection of 'Sayable' items. -- This is essentially a combination of the '&!' and '&*' operators where the -- first operation takes the list of doc items and returns a single item. -- -- > import qualified Prettyprinter as PP -- > -- > putStrLn $ sez @"info" $ t'"The stooges are" &- PP.hsep &!* ["Larry", "Mo", "Curly"] -- The stooges are Larry Mo Curly -- (&!*) :: forall tag m t . (Sayable tag m, Foldable t) => ([PP.Doc SayableAnn] -> PP.Doc SayableAnn) -> t m -> Saying tag pf &!* l = let addElem e (s, p) = ("," <> PP.softline , saying (sayable @tag e) <> s : p) in Saying $ pf $ snd $ foldr addElem ("", []) l infixl 2 &!* -- | A helper operator that applies the first argument (a Prettyprinter -- adaptation function) to the result of a Foldable collection of 'Sayable' -- items. This is essentially a combination of the '&!' and '&*' operators where -- the first operation is applied to the entire list, rather than each element of -- the list (as with `&!*`). (&!$*) :: forall tag m t . (Sayable tag m, Foldable t) => (PP.Doc SayableAnn -> PP.Doc SayableAnn) -> t m -> Saying tag pf &!$* l = let addElem e (s, p) = ("," <> PP.softline , saying (sayable @tag e) <> s <> p) in Saying $ pf $ snd $ foldr addElem ("", mempty) l infixl 2 &!$* -- | A helper operator that applies the first argument which converts -- an array of 'Prettyprinter.Doc ann' elements to a single -- 'PrettyPrinter.Doc ann' element to the second argument, which is a -- Foldable collection of 'Sayable' items. This is essentially a -- combination of the '&!' and '&+*' operators. -- -- Unlike the other operators defined in this package, this is a trinary operator -- rather than a binary operator. Because function application (whitespace) is -- the highest precedence, the last argument will typically need a preceeding $ -- to prevent applying the second argument to the third argument before applying -- this operator. -- -- > import qualified Prettyprinter as PP -- > -- > putStrLn $ sez @"info" $ PP.fillSep &!+* t'" and " $ ["one", "two", "three"] -- one and two and three -- (&!+*) :: forall tag m t b . (Sayable tag b, Sayable tag m, Foldable t) => ([PP.Doc SayableAnn] -> PP.Doc SayableAnn) -> b -> t m -> Saying tag pf &!+* b = let addElem e (s, p) = (Just b, (case s of Nothing -> saying (sayable @tag e) Just x -> saying (sayable @tag e &+ x) ) : p) in Saying . pf . snd . foldr addElem (Nothing, []) infixl 2 &!+* -- | A helper operator allowing a Sayable item to be wrapped in a -- 'Maybe'. This adds the 'Sayable' of the first argument to the -- 'Sayable' of the second argument in the 'Just' case, or just emits -- the 'Sayable' of the first argument if the second argument is -- 'Nothing'. (&?) :: forall tag m e . (Sayable tag m, Sayable tag e) => m -> Maybe e -> Saying tag m &? Nothing = sayable m m &? (Just a) = sayable m <> sayable a infixl 1 &? -- | A helper operator allowing a Sayable item to be wrapped in a 'Maybe' and a -- prettyprinter conversion as the first argument. This is a combination of the -- `&!` and `&?` operators. (&!?) :: forall tag e . (Sayable tag e) => (PP.Doc SayableAnn -> PP.Doc SayableAnn) -> Maybe e -> Saying tag _ &!? Nothing = Saying mempty pf &!? (Just a) = Saying $ pf $ saying $ sayable @tag a infixl 1 &!? -- | A helper operator that generates a newline between its two arguments. Many -- times the '&-' operator is a better choice to allow normal prettyprinter -- layout capabilities, but in situations where it is known that multiple lines -- will or should be generated, this operator makes it easy to separate the -- lines. (&<) :: forall saytag m n . (Sayable saytag m, Sayable saytag n) => m -> n -> Saying saytag m &< n = Saying $ (saying $ sayable @saytag m) <> (PP.line :: PP.Doc SayableAnn) <> (saying $ sayable @saytag n) infixl 1 &< -- | A helper operator that combines '&<' and '&*' which will generate a newline -- between its two arguments, where the second argument is a foldable collection -- whose elements will be sayable emitted with comma separators. (&<*) :: forall saytag m n t . (Sayable saytag m, Sayable saytag n, Foldable t) => m -> t n -> Saying saytag m &<* n = let addElem e (s, Saying p) = (", ", Saying $ saying (sayable @saytag e) <> s <> p) in Saying $ (saying $ sayable @saytag m) <> (PP.line :: PP.Doc SayableAnn) <> (saying $ sayable @saytag (snd $ foldr addElem ("", Saying PP.emptyDoc) n)) infixl 1 &<* -- | A helper operator that emits the first argument and optionally emits a -- newline and the 'Just' value of the second argument if the second argument is -- not 'Nothing' (& m -> Maybe n -> Saying saytag m & (PP.line :: PP.Doc SayableAnn) <> (saying $ sayable @saytag n) infixl 1 & Text t' = id {-# INLINE t' #-} -- | A helper function to use when creating a PP.Doc SayableAnn data -- object (i.e. fixing the @ann@ of 'Doc ann' to 'SayableAnn') d' :: PP.Pretty n => n -> PP.Doc SayableAnn d' = PP.pretty ---------------------------------------------------------------------- -- | This is the default annotation type for the Saying module. The -- Prettyprinter reannotate operation can be used to change this annotation into -- any other annotation type the client desires. -- -- The SayableAnn is an instance of IsLabel, so if OverloadedLabels is enabled, -- this can easily be specified: -- -- @ -- import qualified Prettyprinter as PP -- import Text.Sayable -- -- putStrLn $ sez @"info" $ PP.annotate #myann $ "Hello" &- "world!" -- @ -- -- Note however that labels cannot start with a capital letter. data SayableAnn = SayableAnn Text instance KnownSymbol ann => IsLabel (ann :: Symbol) SayableAnn where fromLabel = SayableAnn $ pack $ symbolVal' (proxy# :: Proxy# ann) ---------------------------------------------------------------------- -- | This is a convenience function that can be used for simple conversions of a -- Sayable to a String. The use of this function is not generally recommended: a -- more controlled rendering of the resulting 'Prettyprinter.Doc' (obtained from -- the via 'saying') is recommended, but there are times (especially when -- debugging) when a quick conversion/extraction to a @String@ is convenient. -- -- This function is often used with a type application: -- -- > putStrLn $ sez @"info" $ "There are" &- length lst &- "list elements." sez :: forall saytag a . Sayable saytag a => a -> String sez = show . saying . sayable @saytag