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 )
34 import TysWiredIn ( mkListTy )
35 import DsMeta ( exprTyConName, declTyConName, decTyConName, qTyConName )
37 import GHC.Base ( unsafeCoerce# ) -- Should have a better home in the module hierarchy
41 %************************************************************************
43 \subsection{Main interface + stubs for the non-GHCI case
45 %************************************************************************
48 tcSpliceDecls :: RenamedHsExpr -> TcM [RdrNameHsDecl]
56 tcSpliceExpr n e ty = pprPanic "Cant do tcSpliceExpr without GHCi" (ppr e)
57 tcSpliceDecls e = pprPanic "Cant do tcSpliceDecls without GHCi" (ppr e)
61 %************************************************************************
63 \subsection{Splicing an expression}
65 %************************************************************************
68 tcBracket :: HsBracket Name -> TcM TcType
69 tcBracket (ExpBr expr)
70 = newTyVarTy openTypeKind `thenM` \ any_ty ->
71 tcMonoExpr expr any_ty `thenM_`
72 tcMetaTy exprTyConName
73 -- Result type is Expr (= Q Exp)
75 tcBracket (DecBr decls)
76 = tcTopSrcDecls decls `thenM_`
77 tcMetaTy decTyConName `thenM` \ decl_ty ->
78 tcMetaTy qTyConName `thenM` \ q_ty ->
79 returnM (mkAppTy q_ty (mkListTy decl_ty))
80 -- Result type is Q [Dec]
84 %************************************************************************
86 \subsection{Splicing an expression}
88 %************************************************************************
91 tcSpliceExpr name expr res_ty
92 = getStage `thenM` \ level ->
93 case spliceOK level of {
94 Nothing -> failWithTc (illegalSplice level) ;
98 Comp -> tcTopSplice expr res_ty ;
99 Brack _ ps_var lie_var ->
101 -- A splice inside brackets
103 -- e.g. [| reverse $(h 4) |]
104 -- Here (h 4) :: Q Exp
105 -- but $(h 4) :: forall a.a i.e. anything!
107 tcMetaTy exprTyConName `thenM` \ meta_exp_ty ->
108 setStage (Splice next_level) (
110 tcMonoExpr expr meta_exp_ty
113 -- Write the pending splice into the bucket
114 readMutVar ps_var `thenM` \ ps ->
115 writeMutVar ps_var ((name,expr') : ps) `thenM_`
117 returnM (panic "tcSpliceExpr") -- The returned expression is ignored
120 -- tcTopSplice used to have this:
121 -- Note that we do not decrement the level (to -1) before
122 -- typechecking the expression. For example:
123 -- f x = $( ...$(g 3) ... )
124 -- The recursive call to tcMonoExpr will simply expand the
125 -- inner escape before dealing with the outer one
127 tcTopSplice expr res_ty
128 = tcMetaTy exprTyConName `thenM` \ meta_exp_ty ->
129 setStage topSpliceStage (
130 getLIE (tcMonoExpr expr meta_exp_ty)
131 ) `thenM` \ (expr', lie) ->
133 -- Solve the constraints
134 tcSimplifyTop lie `thenM` \ const_binds ->
136 q_expr = mkHsLet const_binds expr'
138 zonkTopExpr q_expr `thenM` \ zonked_q_expr ->
140 -- Run the expression
141 traceTc (text "About to run" <+> ppr zonked_q_expr) `thenM_`
142 runMetaE zonked_q_expr `thenM` \ simple_expr ->
145 -- simple_expr :: Meta.Exp
147 expr2 :: RdrNameHsExpr
148 expr2 = convertToHsExpr simple_expr
150 traceTc (text "Got result" <+> ppr expr2) `thenM_`
152 showSplice "expression"
153 zonked_q_expr (ppr expr2) `thenM_`
154 initRn SourceMode (rnExpr expr2) `thenM` \ (exp3, fvs) ->
155 importSupportingDecls fvs `thenM` \ env ->
157 setGblEnv env (tcMonoExpr exp3 res_ty)
161 %************************************************************************
163 \subsection{Splicing an expression}
165 %************************************************************************
168 -- Always at top level
170 = tcMetaTy decTyConName `thenM` \ meta_dec_ty ->
171 tcMetaTy qTyConName `thenM` \ meta_q_ty ->
172 setStage topSpliceStage (
173 getLIE (tcMonoExpr expr (mkAppTy meta_q_ty (mkListTy meta_dec_ty)))
174 ) `thenM` \ (expr', lie) ->
175 -- Solve the constraints
176 tcSimplifyTop lie `thenM` \ const_binds ->
178 q_expr = mkHsLet const_binds expr'
180 zonkTopExpr q_expr `thenM` \ zonked_q_expr ->
182 -- Run the expression
183 traceTc (text "About to run" <+> ppr zonked_q_expr) `thenM_`
184 runMetaD zonked_q_expr `thenM` \ simple_expr ->
186 -- simple_expr :: [Meta.Dec]
187 decls :: [RdrNameHsDecl]
188 decls = convertToHsDecls simple_expr
190 traceTc (text "Got result" <+> vcat (map ppr decls)) `thenM_`
191 showSplice "declarations"
192 zonked_q_expr (vcat (map ppr decls)) `thenM_`
197 %************************************************************************
199 \subsection{Running an expression}
201 %************************************************************************
204 runMetaE :: TypecheckedHsExpr -- Of type (Q Exp)
205 -> TcM Meta.Exp -- Of type Exp
206 runMetaE e = runMeta e
208 runMetaD :: TypecheckedHsExpr -- Of type Q [Dec]
209 -> TcM [Meta.Dec] -- Of type [Dec]
210 runMetaD e = runMeta e
212 -- Warning: if Q is anything other than IO, we need to change this
213 tcRunQ :: Meta.Q a -> TcM a
214 tcRunQ thing = ioToTcRn thing
217 runMeta :: TypecheckedHsExpr -- Of type X
218 -> TcM t -- Of type t
220 = getTopEnv `thenM` \ top_env ->
221 getEps `thenM` \ eps ->
222 getNameCache `thenM` \ name_cache ->
223 getModule `thenM` \ this_mod ->
224 getGlobalRdrEnv `thenM` \ rdr_env ->
226 ghci_mode = top_mode top_env
228 hsc_env = HscEnv { hsc_mode = ghci_mode, hsc_HPT = top_hpt top_env,
229 hsc_dflags = top_dflags top_env }
231 pcs = PCS { pcs_nc = name_cache, pcs_EPS = eps }
233 print_unqual = unQualInScope rdr_env
235 ioToTcRn (HscMain.compileExpr hsc_env pcs this_mod
236 print_unqual expr) `thenM` \ hval ->
238 tryM (tcRunQ (unsafeCoerce# hval)) `thenM` \ either_tval ->
241 Left exn -> failWithTc (vcat [text "Exception when running compile-time code:",
242 nest 4 (vcat [text "Code:" <+> ppr expr,
243 text ("Exn: " ++ show exn)])])
249 -----------------------------------
254 import Lib( g :: Int -> M Exp )
256 f x y = [| \z -> (x, $(g y), z, map, h) |]
258 h p = $( (\q r -> if q then [| \s -> (p,r,s) |]
263 f :: Liftable a => a -> Int -> M Exp
264 f = /\a -> \d::Liftable a ->
265 \ x y -> genSym "z" `bindM` \ z::String ->
266 g y `bindM` \ vv::Exp ->
267 Lam z (Tup [lift d x, v, Var z,
268 Glob "Prelude" "map",
272 h :: Tree Int -> M Exp
273 h = \p -> \s' -> (p,3,s')
278 map: C0 C1 (top-level/imp)
290 f x y = lam "z" (tup [lift x, g y, var "z",
291 [| map |], [| h |] ])
294 f = \x y -> lam "z" (tup [lift d x, g y, var "z",
295 return (Glob "Prelude" "map"),
296 return (Glob "Foo" "h")])
305 h v = [| \x -> map $v x |]
307 g :: Tree Int -> M Exp
310 g x = \x' -> map x x'
312 *** Simon claims x does not have to be liftable! **
316 Level 2 code returned by run time (generation time)
318 Non-top-level variables
321 bound at level 0 --> x
322 bound at level 1 --> var "x"
324 not inside brackets --> x
328 bound at level 0 --> x
329 bound at level 1 --> var "x"
333 Two successive brackets aren't allowed
336 %************************************************************************
338 \subsection{Errors and contexts}
340 %************************************************************************
343 showSplice :: String -> TypecheckedHsExpr -> SDoc -> TcM ()
344 showSplice what before after
345 = getSrcLocM `thenM` \ loc ->
346 traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
347 nest 2 (sep [nest 2 (ppr before),
352 = ptext SLIT("Illegal splice at level") <+> ppr level