[project @ 2005-05-04 10:28:07 by ross]

[ghc-hetmet.git] / ghc / compiler / typecheck / TcRnTypes.lhs

diff --git a/ghc/compiler/typecheck/TcRnTypes.lhs b/ghc/compiler/typecheck/TcRnTypes.lhs
index 3d1329f..ece741f 100644 (file)
--- a/ghc/compiler/typecheck/TcRnTypes.lhs
+++ b/ghc/compiler/typecheck/TcRnTypes.lhs
@@ -26,6 +26,9 @@ module TcRnTypes(
        ThStage(..), topStage, topSpliceStage,
        ThLevel, impLevel, topLevel,
 
+       -- Arrows
+       newArrowScope, escapeArrowScope,
+
        -- Insts
        Inst(..), InstOrigin(..), InstLoc(..), pprInstLoc, 
        instLocSrcLoc, instLocSrcSpan,
@@ -291,6 +294,7 @@ data TcLclEnv               -- Changes as we move inside an expression
        tcl_errs :: TcRef Messages,     -- Place to accumulate errors
 
        tcl_th_ctxt    :: ThStage,      -- Template Haskell context
+       tcl_arrow_ctxt :: ArrowCtxt,    -- Arrow-notation context
 
        tcl_rdr :: LocalRdrEnv,         -- Local name envt
                -- Maintained during renaming, of course, but also during
@@ -367,6 +371,40 @@ topStage, topSpliceStage :: ThStage
 topStage       = Comp
 topSpliceStage = Splice (topLevel - 1) -- Stage for the body of a top-level splice
 
+---------------------------
+-- Arrow-notation context
+---------------------------
+
+{-
+In arrow notation, a variable bound by a proc (or enclosed let/kappa)
+is not in scope to the left of an arrow tail (-<) or the head of (|..|).
+For example
+
+       proc x -> (e1 -< e2)
+
+Here, x is not in scope in e1, but it is in scope in e2.  This can get
+a bit complicated:
+
+       let x = 3 in
+       proc y -> (proc z -> e1) -< e2
+
+Here, x and z are in scope in e1, but y is not.  We implement this by
+recording the environment when passing a proc (using newArrowScope),
+and returning to that (using escapeArrowScope) on the left of -< and the
+head of (|..|).
+-}
+
+newtype ArrowCtxt = ArrowCtxt { arr_proc_env :: Env TcGblEnv TcLclEnv }
+
+-- Record the current environment (outside a proc)
+newArrowScope :: TcM a -> TcM a
+newArrowScope
+  = updEnv $ \env ->
+       env { env_lcl = (env_lcl env) { tcl_arrow_ctxt = ArrowCtxt env } }
+
+-- Return to the stored environment (from the enclosing proc)
+escapeArrowScope :: TcM a -> TcM a
+escapeArrowScope = updEnv (arr_proc_env . tcl_arrow_ctxt . env_lcl)
 
 ---------------------------
 -- TcTyThing