2 % (c) The AQUA Project, Glasgow University, 1996-98
4 \section[CmdLineOpts]{Things to do with command-line options}
29 opt_D_dump_occur_anal,
35 opt_D_dump_simpl_iterations,
36 opt_D_dump_simpl_stats,
42 opt_D_dump_worker_wrapper,
47 opt_D_verbose_core2core,
48 opt_D_verbose_stg2stg,
57 opt_WarnDuplicateExports,
59 opt_WarnIncompletePatterns,
60 opt_WarnMissingMethods,
62 opt_WarnNameShadowing,
63 opt_WarnOverlappingPatterns,
64 opt_WarnSimplePatterns,
67 opt_WarnUnusedImports,
68 opt_WarnUnusedMatches,
71 opt_AutoSccsOnAllToplevs,
72 opt_AutoSccsOnExportedToplevs,
73 opt_AutoSccsOnIndividualCafs,
82 opt_MaxContextReductionDepth,
83 opt_AllowOverlappingInstances,
84 opt_AllowUndecidableInstances,
86 opt_IrrefutableTuples,
94 opt_LiberateCaseThreshold,
96 opt_StgDoLetNoEscapes,
99 opt_UnboxStrictFields,
100 opt_SimplNoPreInlining,
101 opt_SimplDoEtaReduction,
102 opt_SimplDoLambdaEtaExpansion,
106 opt_SimplPedanticBottoms,
109 opt_UF_HiFileThreshold,
110 opt_UF_CreationThreshold,
112 opt_UF_ScrutConDiscount,
113 opt_UF_FunAppDiscount,
114 opt_UF_PrimArgDiscount,
115 opt_UF_KeenessFactor,
121 opt_CompilingPrelude,
122 opt_EmitCExternDecls,
123 opt_EnsureSplittableC,
130 opt_IgnoreIfacePragmas,
132 opt_NoImplicitPrelude,
134 opt_OmitInterfacePragmas,
136 opt_ProduceExportCStubs,
137 opt_ProduceExportHStubs,
154 #include "HsVersions.h"
156 import Array ( array, (//) )
159 import Constants -- Default values for some flags
161 import FastString ( headFS )
162 import Maybes ( assocMaybe, firstJust, maybeToBool )
163 import Panic ( panic, panic# )
165 #if __GLASGOW_HASKELL__ < 301
166 import ArrBase ( Array(..) )
168 import PrelArr ( Array(..) )
172 A command-line {\em switch} is (generally) either on or off; e.g., the
173 ``verbose'' (-v) switch is either on or off. (The \tr{-G<group>}
174 switch is an exception; it's set to a string, or nothing.)
176 A list of {\em ToDo}s is things to be done in a particular part of
177 processing. A (fictitious) example for the Core-to-Core simplifier
178 might be: run the simplifier, then run the strictness analyser, then
179 run the simplifier again (three ``todos'').
181 There are three ``to-do processing centers'' at the moment. In the
182 main loop (\tr{main/Main.lhs}), in the Core-to-Core processing loop
183 (\tr{simplCore/SimplCore.lhs), and in the STG-to-STG processing loop
184 (\tr{simplStg/SimplStg.lhs}).
187 %************************************************************************
189 \subsection{Datatypes associated with command-line options}
191 %************************************************************************
195 = SwBool Bool -- on/off
196 | SwString FAST_STRING -- nothing or a String
197 | SwInt Int -- nothing or an Int
201 data CoreToDo -- These are diff core-to-core passes,
202 -- which may be invoked in any order,
203 -- as many times as you like.
205 = CoreDoSimplify -- The core-to-core simplifier.
206 (SimplifierSwitch -> SwitchResult)
207 -- Each run of the simplifier can take a different
208 -- set of simplifier-specific flags.
215 | CoreDoWorkerWrapper
225 | StgDoUpdateAnalysis
227 | StgDoMassageForProfiling -- should be (next to) last
228 -- There's also setStgVarInfo, but its absolute "lastness"
229 -- is so critical that it is hardwired in (no flag).
234 data SimplifierSwitch
235 = MaxSimplifierIterations Int
236 | SimplInlinePhase Int
239 %************************************************************************
241 \subsection{Classifying command-line options}
243 %************************************************************************
246 lookUp :: FAST_STRING -> Bool
247 lookup_int :: String -> Maybe Int
248 lookup_def_int :: String -> Int -> Int
249 lookup_def_float :: String -> Float -> Float
250 lookup_str :: String -> Maybe String
252 lookUp sw = maybeToBool (assoc_opts sw)
254 lookup_str sw = firstJust (map (startsWith sw) unpacked_opts)
256 lookup_int sw = case (lookup_str sw) of
258 Just xx -> Just (read xx)
260 lookup_def_int sw def = case (lookup_str sw) of
261 Nothing -> def -- Use default
264 lookup_def_char sw def = case (lookup_str sw) of
266 _ -> def -- Use default
268 lookup_def_float sw def = case (lookup_str sw) of
269 Nothing -> def -- Use default
272 assoc_opts = assocMaybe [ (a, True) | a <- argv ]
273 unpacked_opts = map _UNPK_ argv
276 Putting the compiler options into temporary at-files
277 may turn out to be necessary later on if we turn hsc into
278 a pure Win32 application where I think there's a command-line
279 length limit of 255. unpacked_opts understands the @ option.
281 assoc_opts = assocMaybe [ (_PK_ a, True) | a <- unpacked_opts ]
283 unpacked_opts :: [String]
289 expandAts ('@':fname) = words (unsafePerformIO (readFile fname))
295 src_filename :: FAST_STRING
296 src_filename = case argv of
297 filename : rest | headFS filename /= '-' -> filename
298 otherwise -> panic "no filename"
303 opt_D_dump_all {- do not -} = lookUp SLIT("-ddump-all")
304 opt_D_dump_most {- export -} = opt_D_dump_all || lookUp SLIT("-ddump-most")
306 opt_D_dump_absC = opt_D_dump_all || lookUp SLIT("-ddump-absC")
307 opt_D_dump_asm = opt_D_dump_all || lookUp SLIT("-ddump-asm")
308 opt_D_dump_cpranal = opt_D_dump_most || lookUp SLIT("-ddump-cpranal")
309 opt_D_dump_deriv = opt_D_dump_most || lookUp SLIT("-ddump-deriv")
310 opt_D_dump_ds = opt_D_dump_most || lookUp SLIT("-ddump-ds")
311 opt_D_dump_flatC = opt_D_dump_all || lookUp SLIT("-ddump-flatC")
312 opt_D_dump_foreign = opt_D_dump_most || lookUp SLIT("-ddump-foreign-stubs")
313 opt_D_dump_inlinings = opt_D_dump_all || lookUp SLIT("-ddump-inlinings")
314 opt_D_dump_occur_anal = opt_D_dump_most || lookUp SLIT("-ddump-occur-anal")
315 opt_D_dump_parsed = opt_D_dump_most || lookUp SLIT("-ddump-parsed")
316 opt_D_dump_realC = opt_D_dump_all || lookUp SLIT("-ddump-realC")
317 opt_D_dump_rn = opt_D_dump_most || lookUp SLIT("-ddump-rn")
318 opt_D_dump_simpl = opt_D_dump_most || lookUp SLIT("-ddump-simpl")
319 opt_D_dump_simpl_iterations = opt_D_dump_all || lookUp SLIT("-ddump-simpl-iterations")
320 opt_D_dump_spec = opt_D_dump_most || lookUp SLIT("-ddump-spec")
321 opt_D_dump_stg = opt_D_dump_most || lookUp SLIT("-ddump-stg")
322 opt_D_dump_stranal = opt_D_dump_most || lookUp SLIT("-ddump-stranal")
323 opt_D_dump_tc = opt_D_dump_most || lookUp SLIT("-ddump-tc")
324 opt_D_dump_rules = opt_D_dump_most || lookUp SLIT("-ddump-rules")
325 opt_D_dump_usagesp = opt_D_dump_most || lookUp SLIT("-ddump-usagesp")
326 opt_D_dump_cse = opt_D_dump_most || lookUp SLIT("-ddump-cse")
327 opt_D_dump_worker_wrapper = opt_D_dump_most || lookUp SLIT("-ddump-workwrap")
328 opt_D_show_passes = opt_D_dump_most || lookUp SLIT("-dshow-passes")
329 opt_D_dump_rn_trace = opt_D_dump_all || lookUp SLIT("-ddump-rn-trace")
330 opt_D_dump_rn_stats = opt_D_dump_most || lookUp SLIT("-ddump-rn-stats")
331 opt_D_dump_simpl_stats = opt_D_dump_most || lookUp SLIT("-ddump-simpl-stats")
332 opt_D_source_stats = opt_D_dump_most || lookUp SLIT("-dsource-stats")
333 opt_D_verbose_core2core = opt_D_dump_all || lookUp SLIT("-dverbose-simpl")
334 opt_D_verbose_stg2stg = opt_D_dump_all || lookUp SLIT("-dverbose-stg")
336 opt_DoCoreLinting = lookUp SLIT("-dcore-lint")
337 opt_DoStgLinting = lookUp SLIT("-dstg-lint")
338 opt_DoUSPLinting = lookUp SLIT("-dusagesp-lint")
339 opt_PprStyle_NoPrags = lookUp SLIT("-dppr-noprags")
340 opt_PprStyle_Debug = lookUp SLIT("-dppr-debug")
341 opt_PprUserLength = lookup_def_int "-dppr-user-length" 5 --ToDo: give this a name
344 opt_WarnDuplicateExports = lookUp SLIT("-fwarn-duplicate-exports")
345 opt_WarnHiShadows = lookUp SLIT("-fwarn-hi-shadowing")
346 opt_WarnIncompletePatterns = lookUp SLIT("-fwarn-incomplete-patterns")
347 opt_WarnMissingMethods = lookUp SLIT("-fwarn-missing-methods")
348 opt_WarnMissingSigs = lookUp SLIT("-fwarn-missing-signatures")
349 opt_WarnNameShadowing = lookUp SLIT("-fwarn-name-shadowing")
350 opt_WarnOverlappingPatterns = lookUp SLIT("-fwarn-overlapping-patterns")
351 opt_WarnSimplePatterns = lookUp SLIT("-fwarn-simple-patterns")
352 opt_WarnTypeDefaults = lookUp SLIT("-fwarn-type-defaults")
353 opt_WarnUnusedBinds = lookUp SLIT("-fwarn-unused-binds")
354 opt_WarnUnusedImports = lookUp SLIT("-fwarn-unused-imports")
355 opt_WarnUnusedMatches = lookUp SLIT("-fwarn-unused-matches")
358 opt_AutoSccsOnAllToplevs = lookUp SLIT("-fauto-sccs-on-all-toplevs")
359 opt_AutoSccsOnExportedToplevs = lookUp SLIT("-fauto-sccs-on-exported-toplevs")
360 opt_AutoSccsOnIndividualCafs = lookUp SLIT("-fauto-sccs-on-individual-cafs")
361 opt_AutoSccsOnDicts = lookUp SLIT("-fauto-sccs-on-dicts")
362 opt_SccGroup = lookup_str "-G="
363 opt_SccProfilingOn = lookUp SLIT("-fscc-profiling")
364 opt_DoTickyProfiling = lookUp SLIT("-fticky-ticky")
367 opt_AllStrict = lookUp SLIT("-fall-strict")
368 opt_DictsStrict = lookUp SLIT("-fdicts-strict")
369 opt_AllowOverlappingInstances = lookUp SLIT("-fallow-overlapping-instances")
370 opt_AllowUndecidableInstances = lookUp SLIT("-fallow-undecidable-instances")
371 opt_GlasgowExts = lookUp SLIT("-fglasgow-exts")
372 opt_IrrefutableTuples = lookUp SLIT("-firrefutable-tuples")
373 opt_MaxContextReductionDepth = lookup_def_int "-fcontext-stack" mAX_CONTEXT_REDUCTION_DEPTH
374 opt_NumbersStrict = lookUp SLIT("-fnumbers-strict")
375 opt_Parallel = lookUp SLIT("-fparallel")
378 opt_DoEtaReduction = lookUp SLIT("-fdo-eta-reduction")
379 opt_DoSemiTagging = lookUp SLIT("-fsemi-tagging")
380 opt_FoldrBuildOn = lookUp SLIT("-ffoldr-build-on")
381 opt_LiberateCaseThreshold = lookup_def_int "-fliberate-case-threshold" (10::Int)
382 opt_NoPreInlining = lookUp SLIT("-fno-pre-inlining")
383 opt_StgDoLetNoEscapes = lookUp SLIT("-flet-no-escape")
384 opt_UnfoldCasms = lookUp SLIT("-funfold-casms-in-hi-file")
385 opt_UsageSPOn = lookUp SLIT("-fusagesp-on")
386 opt_UnboxStrictFields = lookUp SLIT("-funbox-strict-fields")
389 It's a bit unfortunate to have to re-introduce this chap, but on Win32
390 platforms we do need a way of distinguishing between the case when we're
391 compiling a static version of the Prelude and one that's going to be
392 put into a DLL. Why? Because the compiler's wired in modules need to
393 be attributed as either coming from a DLL or not.
395 opt_CompilingPrelude = lookUp SLIT("-fcompiling-prelude")
396 opt_EmitCExternDecls = lookUp SLIT("-femit-extern-decls")
397 opt_EnsureSplittableC = lookUp SLIT("-fglobalise-toplev-names")
398 opt_GranMacros = lookUp SLIT("-fgransim")
399 opt_HiMap = lookup_str "-himap=" -- file saying where to look for .hi files
400 opt_HiMapSep = lookup_def_char "-himap-sep=" ':'
401 opt_HiVersion = lookup_def_int "-fhi-version=" 0 -- what version we're compiling.
402 opt_HistorySize = lookup_def_int "-fhistory-size" 20
403 opt_IgnoreAsserts = lookUp SLIT("-fignore-asserts")
404 opt_IgnoreIfacePragmas = lookUp SLIT("-fignore-interface-pragmas")
405 opt_NoHiCheck = lookUp SLIT("-fno-hi-version-check")
406 opt_NoImplicitPrelude = lookUp SLIT("-fno-implicit-prelude")
407 opt_OmitBlackHoling = lookUp SLIT("-dno-black-holing")
408 opt_OmitInterfacePragmas = lookUp SLIT("-fomit-interface-pragmas")
409 opt_ProduceC = lookup_str "-C="
410 opt_ProduceExportCStubs = lookup_str "-F="
411 opt_ProduceExportHStubs = lookup_str "-FH="
412 opt_ProduceHi = lookup_str "-hifile=" -- the one to produce this time
414 -- Simplifier switches
415 opt_SimplNoPreInlining = lookUp SLIT("-fno-pre-inlining")
416 -- NoPreInlining is there just to see how bad things
417 -- get if you don't do it!
418 opt_SimplDoEtaReduction = lookUp SLIT("-fdo-eta-reduction")
419 opt_SimplDoLambdaEtaExpansion = lookUp SLIT("-fdo-lambda-eta-expansion")
420 opt_SimplCaseOfCase = lookUp SLIT("-fcase-of-case")
421 opt_SimplCaseMerge = lookUp SLIT("-fcase-merge")
422 opt_SimplLetToCase = lookUp SLIT("-flet-to-case")
423 opt_SimplPedanticBottoms = lookUp SLIT("-fpedantic-bottoms")
426 opt_UF_HiFileThreshold = lookup_def_int "-funfolding-interface-threshold" (30::Int)
427 opt_UF_CreationThreshold = lookup_def_int "-funfolding-creation-threshold" (30::Int)
428 opt_UF_UseThreshold = lookup_def_int "-funfolding-use-threshold" (8::Int) -- Discounts can be big
429 opt_UF_ScrutConDiscount = lookup_def_int "-funfolding-con-discount" (2::Int)
430 opt_UF_FunAppDiscount = lookup_def_int "-funfolding-fun-discount" (6::Int) -- It's great to inline a fn
431 opt_UF_PrimArgDiscount = lookup_def_int "-funfolding-prim-discount" (1::Int)
432 opt_UF_KeenessFactor = lookup_def_float "-funfolding-keeness-factor" (2.0::Float)
434 opt_UF_CheapOp = ( 0 :: Int) -- Only one instruction; and the args are charged for
435 opt_UF_DearOp = ( 4 :: Int)
436 opt_UF_NoRepLit = ( 20 :: Int) -- Strings can be pretty big
438 opt_ProduceS = lookup_str "-S="
439 opt_ReportCompile = lookUp SLIT("-freport-compile")
440 opt_NoPruneDecls = lookUp SLIT("-fno-prune-decls")
441 opt_SourceUnchanged = lookUp SLIT("-fsource-unchanged")
442 opt_Static = lookUp SLIT("-static")
443 opt_Unregisterised = lookUp SLIT("-funregisterised")
444 opt_Verbose = lookUp SLIT("-v")
446 opt_UseVanillaRegs | opt_Unregisterised = 0
447 | otherwise = mAX_Real_Vanilla_REG
448 opt_UseFloatRegs | opt_Unregisterised = 0
449 | otherwise = mAX_Real_Float_REG
450 opt_UseDoubleRegs | opt_Unregisterised = 0
451 | otherwise = mAX_Real_Double_REG
452 opt_UseLongRegs | opt_Unregisterised = 0
453 | otherwise = mAX_Real_Long_REG
457 classifyOpts :: ([CoreToDo], -- Core-to-Core processing spec
458 [StgToDo]) -- STG-to-STG processing spec
460 classifyOpts = sep argv [] [] -- accumulators...
462 sep :: [FAST_STRING] -- cmd-line opts (input)
463 -> [CoreToDo] -> [StgToDo] -- to_do accumulators
464 -> ([CoreToDo], [StgToDo]) -- result
466 sep [] core_td stg_td -- all done!
467 = (reverse core_td, reverse stg_td)
469 # define CORE_TD(to_do) sep opts (to_do:core_td) stg_td
470 # define STG_TD(to_do) sep opts core_td (to_do:stg_td)
472 sep (opt1:opts) core_td stg_td
473 = case (_UNPK_ opt1) of -- the non-"just match a string" options are at the end...
474 ',' : _ -> sep opts core_td stg_td -- it is for the parser
476 "-fsimplify" -> -- gather up SimplifierSwitches specially...
477 simpl_sep opts defaultSimplSwitches core_td stg_td
479 "-ffloat-inwards" -> CORE_TD(CoreDoFloatInwards)
480 "-ffull-laziness" -> CORE_TD(CoreDoFullLaziness)
481 "-fliberate-case" -> CORE_TD(CoreLiberateCase)
482 "-fcse" -> CORE_TD(CoreCSE)
483 "-fprint-core" -> CORE_TD(CoreDoPrintCore)
484 "-fstatic-args" -> CORE_TD(CoreDoStaticArgs)
485 "-fstrictness" -> CORE_TD(CoreDoStrictness)
486 "-fworker-wrapper" -> CORE_TD(CoreDoWorkerWrapper)
487 "-fspecialise" -> CORE_TD(CoreDoSpecialising)
488 "-fusagesp" -> CORE_TD(CoreDoUSPInf)
489 "-fcpr-analyse" -> CORE_TD(CoreDoCPResult)
491 "-fstg-static-args" -> STG_TD(StgDoStaticArgs)
492 "-fupdate-analysis" -> STG_TD(StgDoUpdateAnalysis)
493 "-dstg-stats" -> STG_TD(D_stg_stats)
494 "-flambda-lift" -> STG_TD(StgDoLambdaLift)
495 "-fmassage-stg-for-profiling" -> STG_TD(StgDoMassageForProfiling)
497 _ -> -- NB: the driver is really supposed to handle bad options
498 sep opts core_td stg_td
502 simpl_sep :: [FAST_STRING] -- cmd-line opts (input)
503 -> [SimplifierSwitch] -- simplifier-switch accumulator
504 -> [CoreToDo] -> [StgToDo] -- to_do accumulators
505 -> ([CoreToDo], [StgToDo]) -- result
507 -- "simpl_sep" tailcalls "sep" once it's seen one set
508 -- of SimplifierSwitches for a CoreDoSimplify.
511 simpl_sep input@[] simpl_sw core_td stg_td
512 = panic "simpl_sep []"
515 -- The SimplifierSwitches should be delimited by "[" and "]".
517 simpl_sep (opt1:opts) simpl_sw core_td stg_td
518 = case (_UNPK_ opt1) of
519 "[" -> simpl_sep opts simpl_sw core_td stg_td
521 this_simpl = CoreDoSimplify (isAmongSimpl simpl_sw)
523 sep opts (this_simpl : core_td) stg_td
525 opt -> case matchSimplSw opt of
526 Just sw -> simpl_sep opts (sw:simpl_sw) core_td stg_td
527 Nothing -> simpl_sep opts simpl_sw core_td stg_td
530 = firstJust [ matchSwInt opt "-fmax-simplifier-iterations" MaxSimplifierIterations
531 , matchSwInt opt "-finline-phase" SimplInlinePhase
534 matchSwBool :: String -> String -> a -> Maybe a
535 matchSwBool opt str sw | opt == str = Just sw
536 | otherwise = Nothing
538 matchSwInt :: String -> String -> (Int -> a) -> Maybe a
539 matchSwInt opt str sw = case startsWith str opt of
540 Just opt_left -> Just (sw (read opt_left))
544 %************************************************************************
546 \subsection{Switch ordering}
548 %************************************************************************
550 In spite of the @Produce*@ and @SccGroup@ constructors, these things
551 behave just like enumeration types.
554 instance Eq SimplifierSwitch where
555 a == b = tagOf_SimplSwitch a _EQ_ tagOf_SimplSwitch b
557 instance Ord SimplifierSwitch where
558 a < b = tagOf_SimplSwitch a _LT_ tagOf_SimplSwitch b
559 a <= b = tagOf_SimplSwitch a _LE_ tagOf_SimplSwitch b
562 tagOf_SimplSwitch (SimplInlinePhase _) = ILIT(1)
563 tagOf_SimplSwitch (MaxSimplifierIterations _) = ILIT(2)
565 -- If you add anything here, be sure to change lAST_SIMPL_SWITCH_TAG, too!
567 lAST_SIMPL_SWITCH_TAG = 2
570 %************************************************************************
572 \subsection{Switch lookup}
574 %************************************************************************
577 isAmongSimpl :: [SimplifierSwitch] -> SimplifierSwitch -> SwitchResult
579 isAmongSimpl on_switches -- Switches mentioned later occur *earlier*
580 -- in the list; defaults right at the end.
582 tidied_on_switches = foldl rm_dups [] on_switches
583 -- The fold*l* ensures that we keep the latest switches;
584 -- ie the ones that occur earliest in the list.
586 sw_tbl :: Array Int SwitchResult
587 sw_tbl = (array (0, lAST_SIMPL_SWITCH_TAG) -- bounds...
591 all_undefined = [ (i, SwBool False) | i <- [0 .. lAST_SIMPL_SWITCH_TAG ] ]
593 defined_elems = map mk_assoc_elem tidied_on_switches
595 -- (avoid some unboxing, bounds checking, and other horrible things:)
596 case sw_tbl of { Array bounds_who_needs_'em stuff ->
598 case (indexArray# stuff (tagOf_SimplSwitch switch)) of
599 #if __GLASGOW_HASKELL__ < 400
601 #elif __GLASGOW_HASKELL__ < 403
608 mk_assoc_elem k@(MaxSimplifierIterations lvl) = (IBOX(tagOf_SimplSwitch k), SwInt lvl)
609 mk_assoc_elem k@(SimplInlinePhase n) = (IBOX(tagOf_SimplSwitch k), SwInt n)
610 mk_assoc_elem k = (IBOX(tagOf_SimplSwitch k), SwBool True) -- I'm here, Mom!
612 -- cannot have duplicates if we are going to use the array thing
613 rm_dups switches_so_far switch
614 = if switch `is_elem` switches_so_far
616 else switch : switches_so_far
618 sw `is_elem` [] = False
619 sw `is_elem` (s:ss) = (tagOf_SimplSwitch sw) _EQ_ (tagOf_SimplSwitch s)
623 Default settings for simplifier switches
626 defaultSimplSwitches = [MaxSimplifierIterations 1]
629 %************************************************************************
631 \subsection{Misc functions for command-line options}
633 %************************************************************************
637 switchIsOn :: (switch -> SwitchResult) -> switch -> Bool
639 switchIsOn lookup_fn switch
640 = case (lookup_fn switch) of
641 SwBool False -> False
644 intSwitchSet :: (switch -> SwitchResult)
648 intSwitchSet lookup_fn switch
649 = case (lookup_fn (switch (panic "intSwitchSet"))) of
650 SwInt int -> Just int
655 startsWith :: String -> String -> Maybe String
656 -- startsWith pfx (pfx++rest) = Just rest
658 startsWith [] str = Just str
659 startsWith (c:cs) (s:ss)
660 = if c /= s then Nothing else startsWith cs ss
661 startsWith _ [] = Nothing
663 endsWith :: String -> String -> Maybe String
665 = case (startsWith (reverse cs) (reverse ss)) of
667 Just rs -> Just (reverse rs)