From: simonpj <unknown>
Date: Mon, 15 Oct 2001 15:03:48 +0000 (+0000)
Subject: [project @ 2001-10-15 15:03:48 by simonpj]
X-Git-Tag: Approximately_9120_patches~836
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=3d5a3720e58efcacc7bb9c746f04cb97eabf49a3;p=ghc-hetmet.git

[project @ 2001-10-15 15:03:48 by simonpj]
Add comments re eta expansion
---

diff --git a/ghc/compiler/coreSyn/CorePrep.lhs b/ghc/compiler/coreSyn/CorePrep.lhs
index e03683b..5a4b636 100644
--- a/ghc/compiler/coreSyn/CorePrep.lhs
+++ b/ghc/compiler/coreSyn/CorePrep.lhs
@@ -160,9 +160,11 @@ corePrepRecPairs env pairs
     bndrs = map fst pairs
 
 corePrepRhs :: CloneEnv -> (Id, CoreExpr) -> UniqSM CoreExpr
+	-- Used for top-level bindings, and local recursive bindings
+	-- c.f. mkLocalNonRec, which does the other case
+	-- No nonsense about floating.
+	-- Prepare the RHS and eta expand it. 
 corePrepRhs env (bndr, rhs)
--- Prepare the RHS and eta expand it. 
--- No nonsense about floating
   = corePrepAnExpr env rhs	`thenUs` \ rhs' ->
     getUniquesUs		`thenUs` \ us ->
     returnUs (etaExpand (exprArity rhs') us rhs' (idType bndr))
@@ -416,6 +418,9 @@ mkLocalNonRec bndr dem floats rhs
 	-- because floating the case would make it evaluated too early
 	--
 	-- Finally, eta-expand the RHS, for the benefit of the code gen
+	-- This might not have happened already, because eta expansion
+	-- is done by the simplifier only when there at least one lambda already.
+	--
 	-- NB: we could refrain when the RHS is trivial (which can happen
 	--     for exported things.  This would reduce the amount of code
 	--     generated (a little) and make things a little words for