%************************************************************************
%* *
-\section[vs-Haskell-defn]{Haskell~1.2 vs.~Glasgow Haskell~0.26: language non-compliance}
-\index{GHC vs the Haskell 1.2 language}
-\index{Haskell 1.2 language vs GHC}
+\section[vs-Haskell-defn]{Haskell~1.3 vs.~Glasgow Haskell~2.01: language non-compliance}
+\index{GHC vs the Haskell 1.3 language}
+\index{Haskell 1.3 language vs GHC}
%* *
%************************************************************************
This section lists Glasgow Haskell infelicities in its implementation
-of Haskell~1.2. See also the ``when things go wrong'' section
+of Haskell~1.3. See also the ``when things go wrong'' section
(\sectionref{wrong}) for information about crashes, space leaks, and
other undesirable phenomena.
+GHC~2.01 does not have a ``Haskell~1.2 compatibility mode.'' If
+enough people yelled loudly and long enough, it could conceivably
+happen...
+
The limitations here are listed in Haskell-Report order (roughly).
%Limitations related to Glasgow extensions (unboxed numbers, etc.) are
%given thereafter (\sectionref{infelicities-Glasgow-exts}).
\begin{description}
%-------------------------------------------------------------------
-\item[Some valid irrefutable patterns are rejected:]
-As syntax errors; just put parentheses around them.
+\item[No @n+k@ patterns:]
+We took them out of GHC, because we thought they weren't going to
+survive into Haskell~1.3. But they did. And we haven't put them
+back. Yet.
%-------------------------------------------------------------------
\item[Very long @String@ constants:]
\item[Very long literal lists:]
These may tickle a ``yacc stack overflow'' error in the parser.
(It depends on the Yacc used to build your parser.)
+
+%-------------------------------------------------------------------
+\item[Single quotes in module names:]
+It might work, but it's just begging for trouble.
\end{description}
%************************************************************************
\begin{description}
%-------------------------------------------------------------------
-\item[Contexts on @data@ declarations are ignored:]
-Not that they do much, anyway... This won't wreck your life.
-(We still [vaguely] plan to add them, however.)
-
-%-------------------------------------------------------------------
-\item[Location of instance declarations is unchecked:]
-We don't check that instance declarations occur either in the module
-where the class is declared or the module where the data type is
-declared. This shouldn't hurt you.
-
-For better or worse, we {\em do} check if you try to declare a Prelude
-instance (Prelude class, Prelude type; e.g., \tr{instance Num Bool})
-in one of your own modules. For some reason, people like to do this!
-(But it is not legal Haskell.)
-
-%-------------------------------------------------------------------
-\item[Derived instances of @Text@ for infix constructors:]
+\item[Derived instances of @Read@ and @Show@ for infix constructors:]
All the carry-on about derived @readsPrec@ and @showsPrec@ for infix
constructors---we don't do it (yet). We treat them the same way as
all other constructors.
%-------------------------------------------------------------------
-\item[Derived instances of @Binary@:]
-We don't. (We don't do anything @Binary@ish.)
+\item[Derived instances for records:] Hmmm.
\end{description}
%************************************************************************
\begin{description}
%-------------------------------------------------------------------
-\item[Duplicates in a `renaming' list:]
-Are not reported.
-
-%-------------------------------------------------------------------
-\item[Duplicates in an `import' declaration:]
-These are reported as errors, which some might argue they shouldn't
-be. We reckon it's a feature, not a bug.
-
-%-------------------------------------------------------------------
-\item[Export of `renamed' class methods:]
-Willnae work. That is: you import a class, renaming one or more
-methods; then export that class---the renaming of the methods {\em
-will not} propagate.
-
-(Otherwise, `renaming'---disgusting though it may be---should work.)
-
-%-------------------------------------------------------------------
-\item[Fixities/precedences following `renamed' entities that are exported:]
-No chance.
-
-%-------------------------------------------------------------------
-\item[\tr{import Foo ()} vs \tr{import Foo}:]
-GHC cannot tell the difference (!).
-
-Given that the only module on which you might want to do the former is
-\tr{import Prelude ()}, there are probably much bigger gremlins that
-would jump out and bite you if the import {\em did} work. Besides
-which, you can achieve the same result with
-\tr{-fno-implicit-prelude}.\index{-fno-implicit-prelude option}
-
-%-------------------------------------------------------------------
-\item[Some selective import/export checking not done:]
-On selective import and export of type-constructors/classes in
-which the data-constructors/methods are named explicitly:
-it'll work; it's just that every conceivable paranoia
-check won't be done.
-
-%-------------------------------------------------------------------
-\item[Some Prelude entities cannot be hidden:]
-For example, this doesn't work:
-\begin{verbatim}
-import Prelude hiding (readParen)
-\end{verbatim}
-That's because there are a few should-be-hideable Prelude entities
-which need to appear by magic for derived instances. They are
-\tr{(&&)}, \tr{(.)}, \tr{lex}, \tr{map}, \tr{not}, \tr{readParen},
-\tr{showParen}, and \tr{showString}. SIGH.
-
-%-------------------------------------------------------------------
-\item[\tr{M..} exports vs multiply-imported entities:]
-If an entity \tr{foo} is imported from several interfaces, as in...
-\begin{verbatim}
-import A1 (foo); import A2 (foo); import A3 (foo)
-\end{verbatim}
-... and you then do a ``dot dot'' export of \tr{A1} (for example), it
-will be {\em pure luck} if \tr{foo} gets exported. This is very sad.
-
-Workaround: export \tr{foo} explicitly.
-
-%-------------------------------------------------------------------
-\item[\tr{M..} with Prelude interfaces:]
-Doing \tr{Prelude<something>..} in an export list; don't even think
-it.
-
-%-------------------------------------------------------------------
-\item[Export of Prelude types/classes must be explicit:]
-
-If you want to export a data type, type synonym or class from a
-Prelude module (its name starts with `Prelude'), then it must be
-listed explicitly in the export list. If you say:
-
-\begin{verbatim}
-module PreludeMeGently ( PreludeMeGently.. , other_stuff ) where ..
-\end{verbatim}
-
-then the classes/types in \tr{PreludeMeGently} will {\em not} be
-exported; just add them to the export list. (This shortcoming is only
-likely to affect people writing their own Prelude modules.)
-
-%-------------------------------------------------------------------
\item[Can't export primitives types (e.g., \tr{Int#}):]
Don't even try...
-
-%-------------------------------------------------------------------
-\item[Naming errors with \tr{-O} but not without:]
-
-Documentation by example---Consider a module with these imports:
-
-\begin{verbatim}
-... various imports ...
-import Prettyterm -- desired import
-
-import Pretty -- sadly-needed import
-\end{verbatim}
-
-The \tr{import Pretty} is required because it defines a type
-\tr{Pretty.Doc} which is mentioned in \tr{import Prettyterm}.
-(Extremely sad, but them's the rules.)
-
-But without \tr{-O}, GHC uses its \tr{-fuse-get-mentioned-vars} hack
-(for speed), trying to avoid looking at parts of interfaces that have
-no relevance to this module. As it happens, the thing in
-\tr{Prettyterm} that mentions \tr{Pretty.Doc} is not used here, so
-this module will go through without \tr{import Pretty}. Nice, but
-wrong.
\end{description}
%************************************************************************
\begin{description}
%-------------------------------------------------------------------
-% now in glasgow_exts
-%\item[@fromInt@ method in class @Num@:]
-% (Non-standard.) We support it, as does HBC.
-
-%-------------------------------------------------------------------
\item[Very large/small fractional constants:]
(i.e., with a decimal point somewhere) GHC does not check that these
are out of range (e.g., for a @Float@), and bad things will inevitably
-follow. To be corrected.
+follow. (To be corrected?)
This problem does {\em not} exist for integral constants.
on \tr{Int}, \tr{Float}, and \tr{Double} numbers are {\em unchecked}
for overflow, underflow, and other sad occurrences.
-Use \tr{Integer}, \tr{Rational}, etc., numeric types if this stuff keeps you
-awake at night.
+Use \tr{Integer}, \tr{Rational}, etc., numeric types if this stuff
+keeps you awake at night.
%-------------------------------------------------------------------
\item[Multiply-defined array elements---not checked:]
\begin{verbatim}
main = print (array (1,1) [ 1:=2, 1:=3 ])
\end{verbatim}
-
-%-------------------------------------------------------------------
-\item[Support for @Binary@ whatnot:]
-We don't.
\end{description}
%************************************************************************
%* *
-\subsection[infelicities-IO]{Dialogue I/O}
+\subsection[infelicities-Prelude]{In Prelude support}
%* *
%************************************************************************
-Dialogue-style I/O---still the default for GHC---is on its way out
-(see the stuff about ``monadic I/O for Haskell~1.3''), so we probably
-won't fix these shortcomings.
-
\begin{description}
%-------------------------------------------------------------------
-\item[Support for @Dialogue@ I/O:]
-We do not yet support all @Requests@, notably:
-@ReadBinFile@,
-@WriteBinFile@,
-@AppendBinFile@,
-@StatusFile@,
-@ReadBinChan@,
-@AppendBinChan@,
-@StatusChan@,
-@SetEnv@. Also, we do not support the optional I/O @Requests@.
-
-\item[@AppendChan@ and @ReadChan@ requests:]
-The former only works for \tr{stdout} and \tr{stderr}; the
-latter only for \tr{stdin}.
-
-\item[@Echo@ request:]
-We don't do anything at all.
-\end{description}
-
-%************************************************************************
-%* *
-\subsection[infelicities-Prelude]{In Prelude support}
-%* *
-%************************************************************************
+\item[Polymorphic @seq@:]
+Required by the Haskell~1.3 prelude; not done yet. Consequently,
+the @strict@ function doesn't really do what you want either.
-\begin{description}
%-------------------------------------------------------------------
\item[Arbitrary-sized tuples:]
-Plain old tuples of arbitrary size {\em do} work.
-Note that lots
-of overloading can give rise to large tuples ``under the hood'' of
-your program.
+Plain old tuples of arbitrary size {\em do} work. Note that lots of
+overloading can give rise to large tuples ``under the hood'' of your
+program.
-HOWEVER: standard instances for tuples (@Eq@, @Ord@, @Ix@, and
-@Binary@) are available {\em only} up to 5-tuples; except @Binary@,
-which we don't do at all.
+HOWEVER: standard instances for tuples (@Eq@, @Ord@, @Bounded@, @Ix@
+@Read@, and @Show@) are available {\em only} up to 5-tuples.
These limitations are easily subvertible, so please ask if you get
stuck on them.
\end{description}
-
-%************************************************************************
-%* *
-%\subsection[infelicities-Glasgow-exts]{In Glasgow extensions}
-%* *
-%************************************************************************
-
-%\begin{description}
-%-------------------------------------------------------------------
-%\item[Glasgow extensions not well ``packaged'':]
-%We would rather give you tidy interfaces to the primitive extensions
-%that GHC provides. For example, instead of your having to muck around
-%with...
-%\begin{verbatim}
-% ... _ccall_ fflush ``stderr'' `thenIO_Int_#` ...
-%\end{verbatim}
-%... (all very grimy); you should be able to import a \tr{LibC.hi}, and
-%pretend that @fflush@ is really a Haskell function!
-
-%This problem will be fixed when Haskell~1.3 comes into existence, and
-%we implement it.
-
-%-------------------------------------------------------------------
-%\item[@ArrRef@s of @Int#@s, @Float#@s, @Double#@s:]
-%Are not in yet, but will be. (Easy to add if you're desperate.)
-%\end{description}
-
-%************************************************************************
-%* *
-\section[vs-Haskell-1.3]{Haskell~1.3 DRAFT vs.~Glasgow Haskell~0.26}
-\index{GHC vs the DRAFT Haskell 1.3 language}
-\index{Haskell 1.3 language DRAFT vs GHC}
-%* *
-%************************************************************************
-
-There is work afoot on ``Haskell~1.3,'' a substantial revision of
-the Haskell~1.2 language.
-
-Haskell 1.3 is NOT a standard; it is NOT even a DRAFT standard. As of
-June 1995, there exists a 1.3 PROPOSAL, which will CERTAINLY change.
-Therefore, the ``1.3 things'' we ``support'' may change ARBITRARILY
-much, and we won't even be mildly apologetic about breaking programs
-that use ``1.3'' facilities.
-
-That said, there are two categories of ``1.3'' things that we commend
-to you.
-\begin{itemize}
-\item
-Things virtually certain to end up in any 1.3~standard. An example is
-the \tr{Maybe} type.
-\item
-Wobblier things which are so much better than their 1.2 equivalents
-that you will want to use them. We mean: monadic I/O.
-
-The basic I/O functions are ``unlikely'' to change and so are
-reasonably safe to adopt. (But see WARNING above...)
-\end{itemize}
-
-To use our 1.3 code, you should compile {\em and link} using a
-\tr{-fhaskell-1.3}\index{-fhaskell-1.3 option} flag.
-
-%************************************************************************
-%* *
-\subsection[duffer-1-3]{Duffer's guide for converting 1.2 I/O to 1.3 I/O}
-\index{I/O---converting 1.2 to 1.3}
-\index{Dialogue I/O--converting to 1.3}
-\index{1.2 I/O---converting to 1.3}
-%* *
-%************************************************************************
-
-Here is our ``crib sheet'' for converting 1.2 I/O to 1.3. In most cases,
-it's really easy.
-\begin{enumerate}
-\item
-Change \tr{readChan stdin} to \tr{getContents}.
-\item
-Change \tr{appendChan stdout} to \tr{putStr}, which is equivalent to
-\tr{hPutStr stdout}.
-Change \tr{appendChan stderr} to \tr{hPutStr stderr}.
-\item
-You need to \tr{import System} if you used @getArgs@, @getEnv@,
-or @getProgName@.
-\item
-Assuming continuation-style @Dialogue@ code, change \tr{... exit done $}
-to \tr{... >>}. Change \tr{... exit $ \ foo ->} to \tr{... >>= \ foo ->}.
-\item
-If you had any functions named \tr{(>>)}, \tr{(>>=)}, or \tr{return},
-change them to something else.
-\end{enumerate}
-
-Also:
-1.3 I/O all the way.
-\tr{Dialogue} usually turns into \tr{IO ()}.
-Use of \tr{StatusFile} request: rewrite (no equivalent exists).
-Add \tr{import Ratio} if you use \tr{Rationals} at all.
-Ditto: \tr{import Complex} if you use complex numbers.
-Ditto: \tr{import Array} if you use arrays. Also: note that
-Arrays now use ordinary pairs, rather than a separate \tr{Assoc} type.
-May be easier to do:
-infix 1 =:
-(=:) a b = (a,b)
-and switch := to =:
-This can happen: \tr{LiteralInt.leStringToInt}; add spaces.
-For \tr{minInt}/\tr{maxInt}, \tr{minChar}/\tr{maxChar} (???)
-use the \tr{Bounded} class methods, \tr{minBound} and \tr{maxBound}.
-Replace class \tr{Text} with \tr{Show}; on rare occasions,
-you may need to do something for \tr{Read}, too.
-The functions \tr{ord} and \tr{chr} have been replaced by
-the class methods \tr{fromEnum} and \tr{toEnum}, respectively.
-The changes, however, can lead to ambiguous overloading.
-Need \tr{import IO} for anything interesting.
-What was called \tr{handle} is now called \tr{catch}.
-New keyword: \tr{do}.
-Other clashes: e.g., \tr{seq}, \tr{fail}.
-\tr{readDec} no longer exists; use ???.
-Type of \tr{fail} changed?
-\tr{(a `op` b) c = ...} is bogus.
-`failWith x' now `fail x'
-`fail x' now `fail (userError x)'
-
-%************************************************************************
-%* *
-\subsection[nonio-1-3]{Non-I/O things from the 1.3-DRAFT proposal}
-%* *
-%************************************************************************
-
-Besides the I/O stuff, you also get these things when you use the
-\tr{-fhaskell-1.3}\index{-fhaskell-1.3 option} flag.
-
-Once again: ANY of thing might CHANGE COMPLETELY before we have ``1.3
-for real.''
-
-\begin{verbatim}
-data Either a b = Left a | Right b deriving (Text, Eq, Ord)
-
-data Maybe a = Nothing | Just a deriving (Eq, Ord, Text)
-
-thenMaybe :: Maybe a -> (a -> Maybe b) -> Maybe b
-thenMaybe Nothing _ = Nothing
-thenMaybe (Just x) f = f x
-
-curry :: ((a,b) -> c) -> a -> b -> c
-curry f x y = f (x,y)
-
-uncurry :: (a -> b -> c) -> (a,b) -> c
-uncurry f (x,y) = f x y
-\end{verbatim}
-\index{Maybe type (Haskell 1.3)}
-\index{Either type (Haskell 1.3)}
-\index{curry function (Haskell 1.3)}
-\index{uncurry function (Haskell 1.3)}
-
-%************************************************************************
-%* *
-\subsection[io-1-3]{Vs~1.3 monadic I/O}
-\index{GHC vs the DRAFT 1.3 I/O proposal}
-\index{DRAFT 1.3 I/O proposal vs GHC}
-%* *
-%************************************************************************
-
-The most notable improvement in Haskell~1.3 is its I/O, with a shift to
-``monadic-style'' I/O.
-
-We still offer direct access to the so-called \tr{PrimIO} monad, via
-the \tr{PreludeGlaST} interface. This is NON-STANDARD, an extension.
-This interface is described in \Sectionref{io-1-3-prim-interface}.
-
-The old \tr{PreludePrimIO} interface is DEAD.
-
-The even-older \tr{PreludeGlaIO} interface is DEADER.
-
-%************************************************************************
-%* *
-\subsubsection[io-1-3-shortcomings]{Known shortcomings in monadic I/O}
-%* *
-%************************************************************************
-
-Before you begin with ``1.3-style'' monadic I/O, you might as well
-know the known shortcomings of our implementation, as at 0.26.
-
-The error type is called \tr{IOError13}, rather than \tr{IOError}
-\index{IOError13 vs IOError}
-(which is still the 1.2 type). (Prelude types cannot be renamed,
-so...) You probably shouldn't be messing with \tr{IOError} much,
-anyway.
-
-Some of the 1.3 I/O code, notably the Extremely Cool \tr{Posix}
-stuff, is relatively untested. Go for it, but be wary...
-\index{Posix library bugs}
-\index{bugs, Posix library}
-
-%************************************************************************
-%* *
-\subsubsection[io-1-3-main-interface]{1.3-style monadic I/O}
-%* *
-%************************************************************************
-
-To use our 1.3 I/O, you should compile {\em and link} using a
-\tr{-fhaskell-1.3}\index{-fhaskell-1.3 option} flag.
-
-You should consult the PROPOSED 1.3-I/O standard. GHC~0.26 implements
-the ``December 1994'' draft, which we distribute in
-\tr{ghc/docs/io-1.3/}.
-
-Alternatively, you could grab the ``June 1995'' draft, from
-\tr{pub/haskell/report/}, on \tr{ftp.dcs.glasgow.ac.uk}. The main
-December--June change that you need to know about is: many of the I/O
-functions have been removed from \tr{Prelude*} interfaces (no import
-required) and put into \tr{Lib*} interfaces (import required).
-
-GHC~0.26 still provides the I/O functions via \tr{Prelude.hi} (no
-import required). Ignore the ``June draft'' pleadings for
-\tr{import IO}, and you'll be fine.
-
-{\em There is no guarantee that the final 1.3 proposal will look
-anything like the current DRAFT.} It ain't a standard until the fat
-committee sings.
-
-For interaction with our non-standard \tr{PrimIO}, including
-\tr{_ccall_}s. we also provide:
-\begin{verbatim}
--- impedance matching stuff
-ioToPrimIO :: IO a -> PrimIO a
-\end{verbatim}
-
-%************************************************************************
-%* *
-\subsubsection[io-1-3-prim-interface]{Access to the \tr{PrimIO} monad}
-\index{PrimIO monad (Glasgow extension)}
-\index{I/O, primitive (Glasgow extension)}
-%* *
-%************************************************************************
-
-In what we have implemented, \tr{PrimIO} is the
-handle-the-errors-yourself monad (NB: used for C-calls and such);
-whereas \tr{IO} is the 1.3-ish we-handle-errors-for-you monad.
-
-Should you may need to play with the \tr{PrimIO} monad directly, you
-can import \tr{PreludeGlaST}.
-
-NB: You used to get this stuff from the \tr{PreludePrimIO} interface,
-which is now deceased. As of 0.26, you get all things
-state-transforming from the \tr{PreludeGlaST} interface.
-
-The usual monadic stuff for \tr{PrimIO}:
-\begin{verbatim}
-returnPrimIO :: a -> PrimIO a
-thenPrimIO :: PrimIO a -> (a -> PrimIO b) -> PrimIO b
-seqPrimIO :: PrimIO a -> PrimIO b -> PrimIO b
-fixPrimIO :: (a -> PrimIO a) -> PrimIO a
-foldrPrimIO :: (a -> b -> PrimIO b) -> PrimIO b -> [a] -> PrimIO b
-listPrimIO :: [PrimIO a] -> PrimIO [a]
-mapPrimIO :: (a -> PrimIO b) -> [a] -> PrimIO [b]
-mapAndUnzipPrimIO :: (a -> PrimIO (b,c)) -> [a] -> PrimIO ([b],[c])
-forkPrimIO :: PrimIO a -> PrimIO a
-
-unsafePerformPrimIO :: PrimIO a -> a
-unsafeInterleavePrimIO :: PrimIO a -> PrimIO a
- -- and they are not called "unsafe" for nothing!
-\end{verbatim}
-
-And some other stuff:
-\begin{verbatim}
-data _FILE -- corresponds to a "FILE *" in C
- -- in classes Eq, _CCallable, and _CReturnable
-
-fclose :: _FILE -> PrimIO Int
-fdopen :: Int -> String -> PrimIO _FILE
-fflush :: _FILE -> PrimIO Int
-fopen :: String -> String -> PrimIO _FILE
-fread :: Int -> Int -> _FILE -> PrimIO (Int, _ByteArray Int)
-freopen :: String -> String -> _FILE -> PrimIO _FILE
-fwrite :: _ByteArray Int -> Int -> Int -> _FILE -> PrimIO Int
-
--- please AVOID using these (They will probably die)
-appendChanPrimIO :: String -> String -> PrimIO ()
-appendFilePrimIO :: String -> String -> PrimIO ()
-getArgsPrimIO :: PrimIO [String]
-readChanPrimIO :: String -> PrimIO String
-\end{verbatim}
-
-%************************************************************************
-%* *
-\subsubsection[own-mainPrimIO]{Using your own @mainPrimIO@}
-\index{mainPrimIO, rolling your own}
-%* *
-%************************************************************************
-
-Normally, the GHC runtime system begins things by called an internal
-function @mainPrimIO :: PrimIO ()@ which, in turn, fires up
-@dialogueToIO :: Dialogue -> IO ()@, linking in {\em your} @Main.main@
-to provide the @Dialogue@.
-
-(If you give a \tr{-fhaskell-1.3} flag, then a {\em different}
-@mainPrimIO@ will be linked in---that's why it is important to link
-with \tr{-fhaskell-1.3}...)
-
-To subvert the above process, you need only provide
-a @mainPrimIO :: PrimIO ()@ of your own
-(in a module named \tr{GHCmain}). Do {\em not} use a \tr{-fhaskell-1.3} flag!
-
-Here's a little example, stolen from Alastair Reid:
-\begin{verbatim}
-module GHCmain ( mainPrimIO ) where
-
-import PreludeGlaST
-
-mainPrimIO :: PrimIO ()
-mainPrimIO =
- sleep 5 `seqPrimIO`
- _ccall_ printf "%d\n" (14::Int)
-
-sleep :: Int -> PrimIO ()
-sleep t = _ccall_ sleep t
-\end{verbatim}
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