2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcSplice]{Template Haskell splices}
7 module TcSplice( tcSpliceExpr, tcSpliceDecls, tcBracket ) where
9 #include "HsVersions.h"
11 import HscMain ( compileExpr )
12 import TcRnDriver ( importSupportingDecls, tcTopSrcDecls )
13 -- These imports are the reason that TcSplice
14 -- is very high up the module hierarchy
16 import qualified Language.Haskell.THSyntax as Meta
18 import HscTypes ( HscEnv(..), GhciMode(..), PersistentCompilerState(..), unQualInScope )
19 import HsSyn ( HsBracket(..) )
20 import Convert ( convertToHsExpr, convertToHsDecls )
21 import RnExpr ( rnExpr )
22 import RdrHsSyn ( RdrNameHsExpr, RdrNameHsDecl )
23 import RnHsSyn ( RenamedHsExpr )
24 import TcExpr ( tcMonoExpr )
25 import TcHsSyn ( TcExpr, TypecheckedHsExpr, mkHsLet, zonkTopExpr )
26 import TcSimplify ( tcSimplifyTop )
27 import TcType ( TcType, openTypeKind, mkAppTy )
28 import TcEnv ( spliceOK, tcMetaTy )
29 import TcRnTypes ( TopEnv(..) )
30 import TcMType ( newTyVarTy, zapToType )
34 import TysWiredIn ( mkListTy )
35 import DsMeta ( exprTyConName, declTyConName, decTyConName, qTyConName )
36 import ErrUtils (Message)
38 import Panic ( showException )
39 import GHC.Base ( unsafeCoerce# ) -- Should have a better home in the module hierarchy
44 %************************************************************************
46 \subsection{Main interface + stubs for the non-GHCI case
48 %************************************************************************
51 tcSpliceDecls :: RenamedHsExpr -> TcM [RdrNameHsDecl]
59 tcSpliceExpr n e ty = pprPanic "Cant do tcSpliceExpr without GHCi" (ppr e)
60 tcSpliceDecls e = pprPanic "Cant do tcSpliceDecls without GHCi" (ppr e)
64 %************************************************************************
66 \subsection{Splicing an expression}
68 %************************************************************************
71 tcBracket :: HsBracket Name -> TcM TcType
72 tcBracket (ExpBr expr)
73 = newTyVarTy openTypeKind `thenM` \ any_ty ->
74 tcMonoExpr expr any_ty `thenM_`
75 tcMetaTy exprTyConName
76 -- Result type is Expr (= Q Exp)
78 tcBracket (DecBr decls)
79 = tcTopSrcDecls decls `thenM_`
80 tcMetaTy decTyConName `thenM` \ decl_ty ->
81 tcMetaTy qTyConName `thenM` \ q_ty ->
82 returnM (mkAppTy q_ty (mkListTy decl_ty))
83 -- Result type is Q [Dec]
87 %************************************************************************
89 \subsection{Splicing an expression}
91 %************************************************************************
94 tcSpliceExpr name expr res_ty
95 = getStage `thenM` \ level ->
96 case spliceOK level of {
97 Nothing -> failWithTc (illegalSplice level) ;
101 Comp -> tcTopSplice expr res_ty ;
102 Brack _ ps_var lie_var ->
104 -- A splice inside brackets
105 -- NB: ignore res_ty, apart from zapping it to a mono-type
106 -- e.g. [| reverse $(h 4) |]
107 -- Here (h 4) :: Q Exp
108 -- but $(h 4) :: forall a.a i.e. anything!
110 zapToType res_ty `thenM_`
111 tcMetaTy exprTyConName `thenM` \ meta_exp_ty ->
112 setStage (Splice next_level) (
114 tcMonoExpr expr meta_exp_ty
117 -- Write the pending splice into the bucket
118 readMutVar ps_var `thenM` \ ps ->
119 writeMutVar ps_var ((name,expr') : ps) `thenM_`
121 returnM (panic "tcSpliceExpr") -- The returned expression is ignored
124 -- tcTopSplice used to have this:
125 -- Note that we do not decrement the level (to -1) before
126 -- typechecking the expression. For example:
127 -- f x = $( ...$(g 3) ... )
128 -- The recursive call to tcMonoExpr will simply expand the
129 -- inner escape before dealing with the outer one
131 tcTopSplice expr res_ty
132 = tcMetaTy exprTyConName `thenM` \ meta_exp_ty ->
134 -- Typecheck the expression
135 tcTopSpliceExpr expr meta_exp_ty `thenM` \ zonked_q_expr ->
137 -- Run the expression
138 traceTc (text "About to run" <+> ppr zonked_q_expr) `thenM_`
139 runMetaE zonked_q_expr `thenM` \ simple_expr ->
142 -- simple_expr :: Meta.Exp
144 expr2 :: RdrNameHsExpr
145 expr2 = convertToHsExpr simple_expr
147 traceTc (text "Got result" <+> ppr expr2) `thenM_`
149 showSplice "expression"
150 zonked_q_expr (ppr expr2) `thenM_`
151 initRn SourceMode (rnExpr expr2) `thenM` \ (exp3, fvs) ->
152 importSupportingDecls fvs `thenM` \ env ->
154 setGblEnv env (tcMonoExpr exp3 res_ty)
157 tcTopSpliceExpr :: RenamedHsExpr -> TcType -> TcM TypecheckedHsExpr
158 tcTopSpliceExpr expr meta_ty
159 = checkNoErrs $ -- checkNoErrs: must not try to run the thing
160 -- if the type checker fails!
162 setStage topSpliceStage $
164 -- Typecheck the expression
165 getLIE (tcMonoExpr expr meta_ty) `thenM` \ (expr', lie) ->
167 -- Solve the constraints
168 tcSimplifyTop lie `thenM` \ const_binds ->
171 zonkTopExpr (mkHsLet const_binds expr')
175 %************************************************************************
177 \subsection{Splicing an expression}
179 %************************************************************************
182 -- Always at top level
184 = tcMetaTy decTyConName `thenM` \ meta_dec_ty ->
185 tcMetaTy qTyConName `thenM` \ meta_q_ty ->
187 list_q = mkAppTy meta_q_ty (mkListTy meta_dec_ty)
189 tcTopSpliceExpr expr list_q `thenM` \ zonked_q_expr ->
191 -- Run the expression
192 traceTc (text "About to run" <+> ppr zonked_q_expr) `thenM_`
193 runMetaD zonked_q_expr `thenM` \ simple_expr ->
194 -- simple_expr :: [Meta.Dec]
195 -- decls :: [RdrNameHsDecl]
196 handleErrors (convertToHsDecls simple_expr) `thenM` \ decls ->
197 traceTc (text "Got result" <+> vcat (map ppr decls)) `thenM_`
198 showSplice "declarations"
199 zonked_q_expr (vcat (map ppr decls)) `thenM_`
202 where handleErrors :: [Either a Message] -> TcM [a]
203 handleErrors [] = return []
204 handleErrors (Left x:xs) = liftM (x:) (handleErrors xs)
205 handleErrors (Right m:xs) = do addErrTc m
210 %************************************************************************
212 \subsection{Running an expression}
214 %************************************************************************
217 runMetaE :: TypecheckedHsExpr -- Of type (Q Exp)
218 -> TcM Meta.Exp -- Of type Exp
219 runMetaE e = runMeta e
221 runMetaD :: TypecheckedHsExpr -- Of type Q [Dec]
222 -> TcM [Meta.Dec] -- Of type [Dec]
223 runMetaD e = runMeta e
225 runMeta :: TypecheckedHsExpr -- Of type X
226 -> TcM t -- Of type t
228 = getTopEnv `thenM` \ top_env ->
229 getGblEnv `thenM` \ tcg_env ->
230 getEps `thenM` \ eps ->
231 getNameCache `thenM` \ name_cache ->
232 getModule `thenM` \ this_mod ->
234 ghci_mode = top_mode top_env
236 hsc_env = HscEnv { hsc_mode = ghci_mode, hsc_HPT = top_hpt top_env,
237 hsc_dflags = top_dflags top_env }
239 pcs = PCS { pcs_nc = name_cache, pcs_EPS = eps }
241 type_env = tcg_type_env tcg_env
242 rdr_env = tcg_rdr_env tcg_env
244 -- Wrap the compile-and-run in an exception-catcher
245 -- Compiling might fail if linking fails
246 -- Running might fail if it throws an exception
248 hval <- HscMain.compileExpr
250 rdr_env type_env expr
251 Meta.runQ (unsafeCoerce# hval) -- Coerce it to Q t, and run it
252 )) `thenM` \ either_tval ->
255 Left exn -> failWithTc (vcat [text "Exception when trying to run compile-time code:",
256 nest 4 (vcat [text "Code:" <+> ppr expr,
257 text ("Exn: " ++ Panic.showException exn)])])
263 -----------------------------------
268 import Lib( g :: Int -> M Exp )
270 f x y = [| \z -> (x, $(g y), z, map, h) |]
272 h p = $( (\q r -> if q then [| \s -> (p,r,s) |]
277 f :: Liftable a => a -> Int -> M Exp
278 f = /\a -> \d::Liftable a ->
279 \ x y -> genSym "z" `bindM` \ z::String ->
280 g y `bindM` \ vv::Exp ->
281 Lam z (Tup [lift d x, v, Var z,
282 Glob "Prelude" "map",
286 h :: Tree Int -> M Exp
287 h = \p -> \s' -> (p,3,s')
292 map: C0 C1 (top-level/imp)
304 f x y = lam "z" (tup [lift x, g y, var "z",
305 [| map |], [| h |] ])
308 f = \x y -> lam "z" (tup [lift d x, g y, var "z",
309 return (Glob "Prelude" "map"),
310 return (Glob "Foo" "h")])
319 h v = [| \x -> map $v x |]
321 g :: Tree Int -> M Exp
324 g x = \x' -> map x x'
326 *** Simon claims x does not have to be liftable! **
330 Level 2 code returned by run time (generation time)
332 Non-top-level variables
335 bound at level 0 --> x
336 bound at level 1 --> var "x"
338 not inside brackets --> x
342 bound at level 0 --> x
343 bound at level 1 --> var "x"
347 Two successive brackets aren't allowed
350 %************************************************************************
352 \subsection{Errors and contexts}
354 %************************************************************************
357 showSplice :: String -> TypecheckedHsExpr -> SDoc -> TcM ()
358 showSplice what before after
359 = getSrcLocM `thenM` \ loc ->
360 traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
361 nest 2 (sep [nest 2 (ppr before),
366 = ptext SLIT("Illegal splice at level") <+> ppr level