From 718754ae4f9230b9ecb2e0e47e25e1e101bfe41b Mon Sep 17 00:00:00 2001
From: sof <unknown>
Date: Thu, 21 Jan 1999 20:02:45 +0000
Subject: [PATCH] [project @ 1999-01-21 20:02:43 by sof] Robustified derived
toEnum methods; gives better error message when passed enum tags < 0.
---
ghc/compiler/prelude/PrelInfo.lhs | 2 +-
ghc/compiler/typecheck/TcGenDeriv.lhs | 13 +++++++++----
2 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/ghc/compiler/prelude/PrelInfo.lhs b/ghc/compiler/prelude/PrelInfo.lhs
index 6c4049ea5d81..830247aee6a8 100644
--- a/ghc/compiler/prelude/PrelInfo.lhs
+++ b/ghc/compiler/prelude/PrelInfo.lhs
@@ -606,7 +606,7 @@ deriving_occ_info
, (ordClassKey, [intTyCon_RDR, compose_RDR, eqTag_RDR])
-- EQ (from Ordering) is needed to force in the constructors
-- as well as the type constructor.
- , (enumClassKey, [intTyCon_RDR, map_RDR, plus_RDR, showsPrec_RDR, append_RDR])
+ , (enumClassKey, [intTyCon_RDR, and_RDR, map_RDR, plus_RDR, showsPrec_RDR, append_RDR])
-- The last two Enum deps are only used to produce better
-- error msgs for derived toEnum methods.
, (boundedClassKey, [intTyCon_RDR])
diff --git a/ghc/compiler/typecheck/TcGenDeriv.lhs b/ghc/compiler/typecheck/TcGenDeriv.lhs
index cab4e7c074d7..09e4992c63cc 100644
--- a/ghc/compiler/typecheck/TcGenDeriv.lhs
+++ b/ghc/compiler/typecheck/TcGenDeriv.lhs
@@ -483,11 +483,16 @@ gen_Enum_binds tycon
to_enum
= mk_easy_FunMonoBind tycon_loc toEnum_RDR [a_Pat] [] $
- HsIf (HsApp (HsApp (HsVar gt_RDR)
- (HsVar a_RDR))
- (HsVar (maxtag_RDR tycon)))
- (illegal_toEnum_tag occ_nm (maxtag_RDR tycon))
+ HsIf (HsApp (HsApp
+ (HsVar and_RDR)
+ (HsApp (HsApp (HsVar ge_RDR)
+ (HsVar a_RDR))
+ (HsLit (HsInt 0))))
+ (HsApp (HsApp (HsVar le_RDR)
+ (HsVar a_RDR))
+ (HsVar (maxtag_RDR tycon))))
(mk_easy_App (tag2con_RDR tycon) [a_RDR])
+ (illegal_toEnum_tag occ_nm (maxtag_RDR tycon))
tycon_loc
enum_from
--
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