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
133 -- checkNoErrs: must not try to run the thing
134 -- if the type checker fails!
136 tcMetaTy exprTyConName `thenM` \ meta_exp_ty ->
137 setStage topSpliceStage (
138 getLIE (tcMonoExpr expr meta_exp_ty)
139 ) `thenM` \ (expr', lie) ->
141 -- Solve the constraints
142 tcSimplifyTop lie `thenM` \ const_binds ->
144 -- Wrap the bindings around it and zonk
145 zonkTopExpr (mkHsLet const_binds expr')
146 ) `thenM` \ zonked_q_expr ->
148 -- Run the expression
149 traceTc (text "About to run" <+> ppr zonked_q_expr) `thenM_`
150 runMetaE zonked_q_expr `thenM` \ simple_expr ->
153 -- simple_expr :: Meta.Exp
155 expr2 :: RdrNameHsExpr
156 expr2 = convertToHsExpr simple_expr
158 traceTc (text "Got result" <+> ppr expr2) `thenM_`
160 showSplice "expression"
161 zonked_q_expr (ppr expr2) `thenM_`
162 initRn SourceMode (rnExpr expr2) `thenM` \ (exp3, fvs) ->
163 importSupportingDecls fvs `thenM` \ env ->
165 setGblEnv env (tcMonoExpr exp3 res_ty)
169 %************************************************************************
171 \subsection{Splicing an expression}
173 %************************************************************************
176 -- Always at top level
178 = tcMetaTy decTyConName `thenM` \ meta_dec_ty ->
179 tcMetaTy qTyConName `thenM` \ meta_q_ty ->
180 setStage topSpliceStage (
181 getLIE (tcMonoExpr expr (mkAppTy meta_q_ty (mkListTy meta_dec_ty)))
182 ) `thenM` \ (expr', lie) ->
183 -- Solve the constraints
184 tcSimplifyTop lie `thenM` \ const_binds ->
186 q_expr = mkHsLet const_binds expr'
188 zonkTopExpr q_expr `thenM` \ zonked_q_expr ->
190 -- Run the expression
191 traceTc (text "About to run" <+> ppr zonked_q_expr) `thenM_`
192 runMetaD zonked_q_expr `thenM` \ simple_expr ->
193 -- simple_expr :: [Meta.Dec]
194 -- decls :: [RdrNameHsDecl]
195 handleErrors (convertToHsDecls simple_expr) `thenM` \ decls ->
196 traceTc (text "Got result" <+> vcat (map ppr decls)) `thenM_`
197 showSplice "declarations"
198 zonked_q_expr (vcat (map ppr decls)) `thenM_`
201 where handleErrors :: [Either a Message] -> TcM [a]
202 handleErrors [] = return []
203 handleErrors (Left x:xs) = liftM (x:) (handleErrors xs)
204 handleErrors (Right m:xs) = do addErrTc m
209 %************************************************************************
211 \subsection{Running an expression}
213 %************************************************************************
216 runMetaE :: TypecheckedHsExpr -- Of type (Q Exp)
217 -> TcM Meta.Exp -- Of type Exp
218 runMetaE e = runMeta e
220 runMetaD :: TypecheckedHsExpr -- Of type Q [Dec]
221 -> TcM [Meta.Dec] -- Of type [Dec]
222 runMetaD e = runMeta e
224 runMeta :: TypecheckedHsExpr -- Of type X
225 -> TcM t -- Of type t
227 = getTopEnv `thenM` \ top_env ->
228 getGblEnv `thenM` \ tcg_env ->
229 getEps `thenM` \ eps ->
230 getNameCache `thenM` \ name_cache ->
231 getModule `thenM` \ this_mod ->
233 ghci_mode = top_mode top_env
235 hsc_env = HscEnv { hsc_mode = ghci_mode, hsc_HPT = top_hpt top_env,
236 hsc_dflags = top_dflags top_env }
238 pcs = PCS { pcs_nc = name_cache, pcs_EPS = eps }
240 type_env = tcg_type_env tcg_env
241 rdr_env = tcg_rdr_env tcg_env
243 -- Wrap the compile-and-run in an exception-catcher
244 -- Compiling might fail if linking fails
245 -- Running might fail if it throws an exception
247 hval <- HscMain.compileExpr
249 rdr_env type_env expr
250 Meta.runQ (unsafeCoerce# hval) -- Coerce it to Q t, and run it
251 )) `thenM` \ either_tval ->
254 Left exn -> failWithTc (vcat [text "Exception when trying to run compile-time code:",
255 nest 4 (vcat [text "Code:" <+> ppr expr,
256 text ("Exn: " ++ Panic.showException exn)])])
262 -----------------------------------
267 import Lib( g :: Int -> M Exp )
269 f x y = [| \z -> (x, $(g y), z, map, h) |]
271 h p = $( (\q r -> if q then [| \s -> (p,r,s) |]
276 f :: Liftable a => a -> Int -> M Exp
277 f = /\a -> \d::Liftable a ->
278 \ x y -> genSym "z" `bindM` \ z::String ->
279 g y `bindM` \ vv::Exp ->
280 Lam z (Tup [lift d x, v, Var z,
281 Glob "Prelude" "map",
285 h :: Tree Int -> M Exp
286 h = \p -> \s' -> (p,3,s')
291 map: C0 C1 (top-level/imp)
303 f x y = lam "z" (tup [lift x, g y, var "z",
304 [| map |], [| h |] ])
307 f = \x y -> lam "z" (tup [lift d x, g y, var "z",
308 return (Glob "Prelude" "map"),
309 return (Glob "Foo" "h")])
318 h v = [| \x -> map $v x |]
320 g :: Tree Int -> M Exp
323 g x = \x' -> map x x'
325 *** Simon claims x does not have to be liftable! **
329 Level 2 code returned by run time (generation time)
331 Non-top-level variables
334 bound at level 0 --> x
335 bound at level 1 --> var "x"
337 not inside brackets --> x
341 bound at level 0 --> x
342 bound at level 1 --> var "x"
346 Two successive brackets aren't allowed
349 %************************************************************************
351 \subsection{Errors and contexts}
353 %************************************************************************
356 showSplice :: String -> TypecheckedHsExpr -> SDoc -> TcM ()
357 showSplice what before after
358 = getSrcLocM `thenM` \ loc ->
359 traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
360 nest 2 (sep [nest 2 (ppr before),
365 = ptext SLIT("Illegal splice at level") <+> ppr level