Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: b3c31488 by David Feuer at 2025-08-08T15:33:21-04:00 Add default QuasiQuoters Add `defaultQuasiQuoter` and `namedDefaultQuasiQuoter` to make it easier to write `QuasiQuoters` that give helpful error messages when they're used in inappropriate contexts. Closes #24434. - - - - - 4 changed files: - libraries/ghc-internal/src/GHC/Internal/TH/Quote.hs - libraries/template-haskell/Language/Haskell/TH/Quote.hs - libraries/template-haskell/changelog.md - testsuite/tests/interface-stability/template-haskell-exports.stdout Changes: ===================================== libraries/ghc-internal/src/GHC/Internal/TH/Quote.hs ===================================== @@ -26,10 +26,10 @@ import GHC.Internal.Base hiding (Type) -- | The 'QuasiQuoter' type, a value @q@ of this type can be used -- in the syntax @[q| ... string to parse ...|]@. In fact, for -- convenience, a 'QuasiQuoter' actually defines multiple quasiquoters --- to be used in different splice contexts; if you are only interested --- in defining a quasiquoter to be used for expressions, you would --- define a 'QuasiQuoter' with only 'quoteExp', and leave the other --- fields stubbed out with errors. +-- to be used in different splice contexts. In the usual case of a +-- @QuasiQuoter@ that is only intended to be used in certain splice +-- contexts, the unused fields should just 'fail'. This is most easily +-- accomplished using 'namedefaultQuasiQuoter' or 'defaultQuasiQuoter'. data QuasiQuoter = QuasiQuoter { -- | Quasi-quoter for expressions, invoked by quotes like @lhs = $[q|...]@ quoteExp :: String -> Q Exp, ===================================== libraries/template-haskell/Language/Haskell/TH/Quote.hs ===================================== @@ -16,6 +16,8 @@ that is up to you. module Language.Haskell.TH.Quote ( QuasiQuoter(..) , quoteFile + , namedDefaultQuasiQuoter + , defaultQuasiQuoter -- * For backwards compatibility ,dataToQa, dataToExpQ, dataToPatQ ) where @@ -39,3 +41,54 @@ quoteFile (QuasiQuoter { quoteExp = qe, quotePat = qp, quoteType = qt, quoteDec get old_quoter file_name = do { file_cts <- runIO (readFile file_name) ; addDependentFile file_name ; old_quoter file_cts } + +-- | A 'QuasiQuoter' that fails with a helpful error message in every +-- context. It is intended to be modified to create a 'QuasiQuoter' that +-- fails in all inappropriate contexts. +-- +-- For example, you could write +-- +-- @ +-- myPatQQ = (namedDefaultQuasiQuoter "myPatQQ") +-- { quotePat = ... } +-- @ +-- +-- If 'myPatQQ' is used in an expression context, the compiler will report +-- that, naming 'myPatQQ'. +-- +-- See also 'defaultQuasiQuoter', which does not name the 'QuasiQuoter' in +-- the error message, and might therefore be more appropriate when +-- the users of a particular 'QuasiQuoter' tend to define local \"synonyms\" +-- for it. +namedDefaultQuasiQuoter :: String -> QuasiQuoter +namedDefaultQuasiQuoter name = QuasiQuoter + { quoteExp = f "use in expression contexts." + , quotePat = f "use in pattern contexts." + , quoteType = f "use in types." + , quoteDec = f "creating declarations." + } + where + f m _ = fail $ "The " ++ name ++ " quasiquoter is not for " ++ m + +-- | A 'QuasiQuoter' that fails with a helpful error message in every +-- context. It is intended to be modified to create a 'QuasiQuoter' that +-- fails in all inappropriate contexts. +-- +-- For example, you could write +-- +-- @ +-- myExpressionQQ = defaultQuasiQuoter +-- { quoteExp = ... } +-- @ +-- +-- See also 'namedDefaultQuasiQuoter', which names the 'QuasiQuoter' in the +-- error messages. +defaultQuasiQuoter :: QuasiQuoter +defaultQuasiQuoter = QuasiQuoter + { quoteExp = f "use in expression contexts." + , quotePat = f "use in pattern contexts." + , quoteType = f "use in types." + , quoteDec = f "creating declarations." + } + where + f m _ = fail $ "This quasiquoter is not for " ++ m ===================================== libraries/template-haskell/changelog.md ===================================== @@ -1,5 +1,8 @@ # Changelog for [`template-haskell` package](http://hackage.haskell.org/package/template-haskell) +## 2.25.0.0 + * Introduce `namedDefaultQuasiQuoter` and `defaultQuasiQuoter`, which fail with a helpful error when used in an inappropriate context. + ## 2.24.0.0 * Introduce `dataToCodeQ` and `liftDataTyped`, typed variants of `dataToExpQ` and `liftData` respectively. ===================================== testsuite/tests/interface-stability/template-haskell-exports.stdout ===================================== @@ -1370,6 +1370,8 @@ module Language.Haskell.TH.Quote where dataToExpQ :: forall (m :: * -> *) a. (GHC.Internal.TH.Syntax.Quote m, GHC.Internal.Data.Data.Data a) => (forall b. GHC.Internal.Data.Data.Data b => b -> GHC.Internal.Maybe.Maybe (m GHC.Internal.TH.Syntax.Exp)) -> a -> m GHC.Internal.TH.Syntax.Exp dataToPatQ :: forall (m :: * -> *) a. (GHC.Internal.TH.Syntax.Quote m, GHC.Internal.Data.Data.Data a) => (forall b. GHC.Internal.Data.Data.Data b => b -> GHC.Internal.Maybe.Maybe (m GHC.Internal.TH.Syntax.Pat)) -> a -> m GHC.Internal.TH.Syntax.Pat dataToQa :: forall (m :: * -> *) a k q. (GHC.Internal.TH.Syntax.Quote m, GHC.Internal.Data.Data.Data a) => (GHC.Internal.TH.Syntax.Name -> k) -> (GHC.Internal.TH.Syntax.Lit -> m q) -> (k -> [m q] -> m q) -> (forall b. GHC.Internal.Data.Data.Data b => b -> GHC.Internal.Maybe.Maybe (m q)) -> a -> m q + defaultQuasiQuoter :: QuasiQuoter + namedDefaultQuasiQuoter :: GHC.Internal.Base.String -> QuasiQuoter quoteFile :: QuasiQuoter -> QuasiQuoter module Language.Haskell.TH.Syntax where @@ -1720,8 +1722,8 @@ module Language.Haskell.TH.Syntax where qAddForeignFilePath :: ForeignSrcLang -> GHC.Internal.Base.String -> m () qAddModFinalizer :: Q () -> m () qAddCorePlugin :: GHC.Internal.Base.String -> m () - qGetQ :: forall a. ghc-internal-9.1300.0:GHC.Internal.Data.Typeable.Internal.Typeable a => m (GHC.Internal.Maybe.Maybe a) - qPutQ :: forall a. ghc-internal-9.1300.0:GHC.Internal.Data.Typeable.Internal.Typeable a => a -> m () + qGetQ :: forall a. ghc-internal-9.1500.0:GHC.Internal.Data.Typeable.Internal.Typeable a => m (GHC.Internal.Maybe.Maybe a) + qPutQ :: forall a. ghc-internal-9.1500.0:GHC.Internal.Data.Typeable.Internal.Typeable a => a -> m () qIsExtEnabled :: Extension -> m GHC.Internal.Types.Bool qExtsEnabled :: m [Extension] qPutDoc :: DocLoc -> GHC.Internal.Base.String -> m () @@ -1802,7 +1804,7 @@ module Language.Haskell.TH.Syntax where falseName :: Name getDoc :: DocLoc -> Q (GHC.Internal.Maybe.Maybe GHC.Internal.Base.String) getPackageRoot :: Q GHC.Internal.IO.FilePath - getQ :: forall a. ghc-internal-9.1300.0:GHC.Internal.Data.Typeable.Internal.Typeable a => Q (GHC.Internal.Maybe.Maybe a) + getQ :: forall a. ghc-internal-9.1500.0:GHC.Internal.Data.Typeable.Internal.Typeable a => Q (GHC.Internal.Maybe.Maybe a) get_cons_names :: Con -> [Name] hoistCode :: forall (m :: * -> *) (n :: * -> *) (r :: GHC.Internal.Types.RuntimeRep) (a :: TYPE r). GHC.Internal.Base.Monad m => (forall x. m x -> n x) -> Code m a -> Code n a isExtEnabled :: Extension -> Q GHC.Internal.Types.Bool @@ -1849,7 +1851,7 @@ module Language.Haskell.TH.Syntax where oneName :: Name pkgString :: PkgName -> GHC.Internal.Base.String putDoc :: DocLoc -> GHC.Internal.Base.String -> Q () - putQ :: forall a. ghc-internal-9.1300.0:GHC.Internal.Data.Typeable.Internal.Typeable a => a -> Q () + putQ :: forall a. ghc-internal-9.1500.0:GHC.Internal.Data.Typeable.Internal.Typeable a => a -> Q () recover :: forall a. Q a -> Q a -> Q a reify :: Name -> Q Info reifyAnnotations :: forall a. GHC.Internal.Data.Data.Data a => AnnLookup -> Q [a] View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b3c3148806014e3c36fc91b8710c46db... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b3c3148806014e3c36fc91b8710c46db... You're receiving this email because of your account on gitlab.haskell.org.