X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fusing.xml;h=06b9ccc315a6ad52eb4f500c3f18fcd2b9439e07;hb=58521c72cec262496dabf5fffb057d25ab17a0f7;hp=439fb58c90b6ba96d19432e3d75b264d2e0c86bd;hpb=a078252410f284229e5f2440e7b8a9b32a6cfd33;p=ghc-hetmet.git
diff --git a/docs/users_guide/using.xml b/docs/users_guide/using.xml
index 439fb58..06b9ccc 100644
--- a/docs/users_guide/using.xml
+++ b/docs/users_guide/using.xml
@@ -46,26 +46,25 @@ ghc [argument...]
Sometimes it is useful to make the connection between a
source file and the command-line options it requires quite
- tight. For instance, if a Haskell source file uses GHC
- extensions, it will always need to be compiled with the
- option. Rather than maintaining
+ tight. For instance, if a Haskell source file deliberately
+ uses name shadowing, it should be compiled with the
+ option. Rather than maintaining
the list of per-file options in a Makefile,
it is possible to do this directly in the source file using the
OPTIONS_GHC pragma OPTIONS_GHC
pragma:
-{-# OPTIONS_GHC -fglasgow-exts #-}
+{-# OPTIONS_GHC -fno-warn-name-shadowing #-}
module X where
...
- OPTIONS_GHC pragmas are only looked for at
- the top of your source files, upto the first
- (non-literate,non-empty) line not containing
- OPTIONS_GHC. Multiple OPTIONS_GHC
- pragmas are recognised. Do not put comments before, or on the same line
- as, the OPTIONS_GHC pragma.
+ OPTIONS_GHC is a file-header pragma
+ (see ).
+
+ Only dynamic flags can be used in an OPTIONS_GHC pragma
+ (see ).Note that your command shell does not
get to the source file options, they are just included literally
@@ -121,7 +120,7 @@ module X where
Most non-mode flags fall into this category. A dynamic flag
may be used on the command line, in a
- GHC_OPTIONS pragma in a source file, or set
+ OPTIONS_GHC pragma in a source file, or set
using :set in GHCi.
@@ -845,7 +844,9 @@ ghc -c Foo.hs
,
,
,
- , and
+ ,
+ ,
+ , and
. The following
flags are
simple ways to select standard “packages” of warnings:
@@ -859,6 +860,7 @@ ghc -c Foo.hs
-W optionProvides the standard warnings plus
,
+ ,
,
,
, and
@@ -877,7 +879,8 @@ ghc -c Foo.hs
,
,
,
- , and
+ ,
+ , and
.
@@ -919,6 +922,23 @@ ghc -c Foo.hs
+ :
+
+
+
+ warnings
+ pragmas
+ Causes a warning to be emitted when a
+ pragma that GHC doesn't recognise is used. As well as pragmas
+ that GHC itself uses, GHC also recognises pragmas known to be used
+ by other tools, e.g. OPTIONS_HUGS and
+ DERIVE.
+
+ This option is on by default.
+
+
+
+ :
@@ -972,11 +992,25 @@ foreign import "&f" f :: FunPtr t
+ :
+
+
+
+ Causes a warning to be emitted when a datatype
+ T is exported
+ with all constructors, i.e. T(..), but is it
+ just a type synonym.
+ Also causes a warning to be emitted when a module is
+ re-exported, but that module exports nothing.
+
+
+
+ :
- Causes a warning to be emitted when a a datatype
+ Causes a warning to be emitted when a datatype
T is imported
with all constructors, i.e. T(..), but has been
exported abstractly, i.e. T.
@@ -984,6 +1018,20 @@ foreign import "&f" f :: FunPtr t
+ :
+
+
+
+ Causes a warning to be emitted when an unlifted type
+ is bound in a way that looks lazy, e.g.
+ where (I# x) = .... Use
+ where !(I# x) = ... instead. This will be an
+ error, rather than a warning, in GHC 6.14.
+
+
+
+
+ :
@@ -1159,6 +1207,11 @@ f foo = foo { x = 6 }
typographical errors that turn into hard-to-find bugs, e.g.,
in the inadvertent capture of what would be a recursive call in
f = ... let f = id in ... f ....
+ The warning is suppressed for names beginning with an underscore. For example
+
+ f x = do { _ignore <- this; _ignore <- that; return (the other) }
+
+
@@ -1329,6 +1382,56 @@ f "2" = 2
+
+ :
+
+
+ unused do binding, warning
+ do binding, unused
+
+ Report expressions occuring in do and mdo blocks
+ that appear to silently throw information away.
+ For instance do { mapM popInt xs ; return 10 } would report
+ the first statement in the do block as suspicious,
+ as it has the type StackM [Int] and not StackM (), but that
+ [Int] value is not bound to anything. The warning is suppressed by
+ explicitly mentioning in the source code that your program is throwing something away:
+
+ do { _ <- mapM popInt xs ; return 10 }
+
+ Of course, in this particular situation you can do even better:
+
+ do { mapM_ popInt xs ; return 10 }
+
+
+
+
+
+
+ :
+
+
+ apparently erroneous do binding, warning
+ do binding, apparently erroneous
+
+ Report expressions occuring in do and mdo blocks
+ that appear to lack a binding.
+ For instance do { return (popInt 10) ; return 10 } would report
+ the first statement in the do block as suspicious,
+ as it has the type StackM (StackM Int) (which consists of two nested applications
+ of the same monad constructor), but which is not then "unpacked" by binding the result.
+ The warning is suppressed by explicitly mentioning in the source code that your program is throwing something away:
+
+ do { _ <- return (popInt 10) ; return 10 }
+
+ For almost all sensible programs this will indicate a bug, and you probably intended to write:
+
+ do { popInt 10 ; return 10 }
+
+
+
+
+
If you're feeling really paranoid, the
@@ -1707,7 +1810,9 @@ f "2" = 2
&phases;
-
+
+ &shared_libs;
+
Using Concurrent HaskellConcurrent Haskellusing
@@ -1818,7 +1923,7 @@ f "2" = 2
-
+ RTS option
Use x simultaneous threads when
@@ -1830,9 +1935,19 @@ f "2" = 2
on a dual-core machine we would probably use
+RTS -N2 -RTS.
+ Omitting x,
+ i.e. +RTS -N -RTS, lets the runtime
+ choose the value of x itself
+ based on how many processors are in your machine.
+
+ Be careful when using all the processors in your
+ machine: if some of your processors are in use by other
+ programs, this can actually harm performance rather than
+ improve it.
+
Setting also has the effect of
- setting (the number of OS threads to
- use for garbage collection) to the same value.
+ enabling the parallel garbage collector (see
+ ).There is no means (currently) by which this value
may vary after the program has started.