X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fusing.xml;h=115c290491f97c61f766e70ef4f35636c2180502;hb=3bb700d515de2405fa5db3326482e529f332d508;hp=8b876204ece31167c7ccce065d0a03d622ead402;hpb=058b5c20ba7bb3adc4f130ff24893c13941eca4d;p=ghc-hetmet.git
diff --git a/docs/users_guide/using.xml b/docs/users_guide/using.xml
index 8b87620..115c290 100644
--- a/docs/users_guide/using.xml
+++ b/docs/users_guide/using.xml
@@ -6,6 +6,77 @@
using GHC
+ Getting started: compiling programs
+
+
+ In this chapter you'll find a complete reference to the GHC
+ command-line syntax, including all 400+ flags. It's a large and
+ complex system, and there are lots of details, so it can be
+ quite hard to figure out how to get started. With that in mind,
+ this introductory section provides a quick introduction to the
+ basic usage of GHC for compiling a Haskell program, before the
+ following sections dive into the full syntax.
+
+
+
+ Let's create a Hello World program, and compile and run it.
+ First, create a file hello.hs containing
+ the Haskell code:
+
+
+
+main = putStrLn "Hello, World!"
+
+
+ To compile the program, use GHC like this:
+
+
+$ ghc hello.hs
+
+ (where $ represents the prompt: don't
+ type it). GHC will compile the source
+ file hello.hs, producing
+ an object
+ filehello.o and
+ an interface
+ filehello.hi, and then it
+ will link the object file to the libraries that come with GHC
+ to produce an executable called hello on
+ Unix/Linux/Mac, or hello.exe on
+ Windows.
+
+
+ By default GHC will be very quiet about what it is doing, only
+ printing error messages. If you want to see in more detail
+ what's going on behind the scenes, add to
+ the command line.
+
+
+
+ Then we can run the program like this:
+
+
+
+$ ./hello
+Hello World!
+
+
+ If your program contains multiple modules, then you only need to
+ tell GHC the name of the source file containing
+ the Main module, and GHC will examine
+ the import declarations to find the other
+ modules that make up the program and find their source files.
+ This means that, with the exception of
+ the Main module, every source file should be
+ named after the module name that it contains (with dots replaced
+ by directory separators). For example, the
+ module Data.Person would be in the
+ file Data/Person.hs on Unix/Linux/Mac,
+ or Data\Person.hs on Windows.
+
+
+
+ Options overviewGHC's behaviour is controlled by
@@ -110,7 +181,7 @@ module X where
Mode flags
- For example, or .
+ For example, or .
There may only be a single mode flag on the command line. The
available modes are listed in .
@@ -197,6 +268,22 @@ module X where
+ .ll
+
+ An llvm-intermediate-language source file, usually
+ produced by the compiler.
+
+
+
+
+ .bc
+
+ An llvm-intermediate-language bitcode file, usually
+ produced by the compiler.
+
+
+
+ .sAn assembly-language source file, usually produced by
@@ -220,10 +307,20 @@ module X where
Modes of operation
- GHC's behaviour is firstly controlled by a mode flag. Only
- one of these flags may be given, but it does not necessarily need
- to be the first option on the command-line. The available modes
- are:
+
+ GHC's behaviour is firstly controlled by a mode flag. Only one
+ of these flags may be given, but it does not necessarily need to
+ be the first option on the command-line.
+
+
+
+ If no mode flag is present, then GHC will enter make mode
+ () if there are any Haskell source
+ files given on the command line, or else it will link the
+ objects named on the command line to produce an executable.
+
+
+ The available mode flags are:
@@ -242,7 +339,7 @@ module X where
- ghc --make
+ ghc ––makemake mode
@@ -254,6 +351,12 @@ module X where
likely to be much easier, and faster, than using
make. Make mode is described in .
+
+
+ This mode is the default if there are any Haskell
+ source files mentioned on the command line, and in this case
+ the option can be omitted.
+
@@ -355,9 +458,10 @@ module X where
+ ghc --supported-extensionsghc --supported-languages
-
+ Print the supported language extensions.
@@ -428,8 +532,7 @@ module X where
separate compilation
- When given the option,
- GHC will build a multi-module Haskell program by following
+ In this mode, GHC will build a multi-module Haskell program by following
dependencies from one or more root modules (usually just
Main). For example, if your
Main module is in a file called
@@ -440,12 +543,22 @@ module X where
ghc ––make Main.hs
- The command line may contain any number of source file
- names or module names; GHC will figure out all the modules in
- the program by following the imports from these initial modules.
- It will then attempt to compile each module which is out of
- date, and finally, if there is a Main module,
- the program will also be linked into an executable.
+
+ In fact, GHC enters make mode automatically if there are any
+ Haskell source files on the command line and no other mode is
+ specified, so in this case we could just type
+
+
+
+ghc Main.hs
+
+
+ Any number of source file names or module names may be
+ specified; GHC will figure out all the modules in the program by
+ following the imports from these initial modules. It will then
+ attempt to compile each module which is out of date, and
+ finally, if there is a Main module, the
+ program will also be linked into an executable.The main advantages to using ghc
––make over traditional
@@ -844,7 +957,9 @@ ghc -c Foo.hs
,
,
,
- , and
+ ,
+ ,
+ , and
. The following
flags are
simple ways to select standard “packages” of warnings:
@@ -858,6 +973,7 @@ ghc -c Foo.hs
-W optionProvides the standard warnings plus
,
+ ,
,
,
, and
@@ -873,10 +989,12 @@ ghc -c Foo.hs
suspicious code. The warnings that are
not enabled by
are
- ,
,
+ ,
,
- , and
+ ,
+ ,
+ ,
.
@@ -988,11 +1106,25 @@ 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.
@@ -1000,6 +1132,20 @@ 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 7.2.
+
+
+
+
+ :
@@ -1031,6 +1177,21 @@ foreign import "&f" f :: FunPtr t
+ :
+
+
+ Causes the compiler to emit a warning when a Prelude numeric
+ conversion converts a type T to the same type T; such calls
+ are probably no-ops and can be omitted. The functions checked for
+ are: toInteger,
+ toRational,
+ fromIntegral,
+ and realToFrac.
+
+
+
+
+ :
@@ -1056,26 +1217,41 @@ foreign import "&f" f :: FunPtr t
- :
+ ,
+ :
+
+ incomplete patterns, warningpatterns, incomplete
- Similarly for incomplete patterns, the function
+ The option warns
+ about places where
+ a pattern-match might fail at runtime.
+ The function
g below will fail when applied to
non-empty lists, so the compiler will emit a warning about
this when is
- enabled.
-
+ enabled.
g [] = 2
-
- This option isn't enabled by default because it can be
+ This option isn't enabled by default because it can be
a bit noisy, and it doesn't always indicate a bug in the
program. However, it's generally considered good practice
- to cover all the cases in your functions.
+ to cover all the cases in your functions, and it is switched
+ on by .
+
+ The flag is
+ similar, except that it
+ applies only to lambda-expressions and pattern bindings, constructs
+ that only allow a single pattern:
+
+h = \[] -> 2
+Just k = f y
+
+
@@ -1124,6 +1300,39 @@ f foo = foo { x = 6 }
+
+ :
+
+ missing import lists, warning
+ import lists, missing
+
+
+
+ This flag warns if you use an unqualified
+ import declaration
+ that does not explicitly list the entities brought into scope. For
+ example
+
+
+module M where
+ import X( f )
+ import Y
+ import qualified Z
+ p x = f x x
+
+
+ The flag will warn about the import
+ of Y but not X
+ If module Y is later changed to export (say) f,
+ then the reference to f in M will become
+ ambiguous. No warning is produced for the import of Z
+ because extending Z's exports would be unlikely to produce
+ ambiguity in M.
+
+
+
+
+ :
@@ -1164,6 +1373,20 @@ f foo = foo { x = 6 }
+ :
+
+
+ type signatures, missing
+
+ If you use the
+ flag GHC will warn
+ you about any polymorphic local bindings. As part of
+ the warning GHC also reports the inferred type. The
+ option is off by default.
+
+
+
+ :
@@ -1175,6 +1398,11 @@ 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) }
+
+
@@ -1226,28 +1454,6 @@ f "2" = 2
- :
-
-
-
- Causes the compiler to warn about lambda-bound
- patterns that can fail, eg. \(x:xs)->....
- Normally, these aren't treated as incomplete patterns by
- .
- “Lambda-bound patterns” includes all places where there is a single pattern,
- including list comprehensions and do-notation. In these cases, a pattern-match
- failure is quite legitimate, and triggers filtering (list comprehensions) or
- the monad fail operation (monads). For example:
-
- f :: [Maybe a] -> [a]
- f xs = [y | Just y <- xs]
-
- Switching on will elicit warnings about
- these probably-innocent cases, which is why the flag is off by default.
-
-
-
- :
@@ -1271,6 +1477,7 @@ f "2" = 2
e.g., the ‘default default’ for Haskell 1.4 caused the
otherwise unconstrained value 1 to be
given the type Int, whereas Haskell 98
+ and later
defaults it to Integer. This may lead to
differences in performance and behaviour, hence the
usefulness of being non-silent about this.
@@ -1345,6 +1552,56 @@ 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
@@ -1453,37 +1710,12 @@ f "2" = 2
.
-
-
-
- :
- -Ofile <file> option
- optimising, customised
-
-
- (NOTE: not supported since GHC 4.x. Please ask if
- you're interested in this.)
-
- For those who need absolute
- control over exactly what options are
- used (e.g., compiler writers, sometimes :-), a list of
- options can be put in a file and then slurped in with
- .
-
- In that file, comments are of the
- #-to-end-of-line variety; blank
- lines and most whitespace is ignored.
-
- Please ask if you are baffled and would like an
- example of !
-
- We don't use a flag for day-to-day
work. We use to get respectable speed;
e.g., when we want to measure something. When we want to go for
- broke, we tend to use (and we go for
+ broke, we tend to use (and we go for
lots of coffee breaks).The easiest way to see what (etc.)
@@ -1580,6 +1812,26 @@ f "2" = 2
+
+
+
+
+ Turns off the float-in transformation.
+
+
+
+
+
+
+
+
+
+ Turns off the automatic specialisation of overloaded functions.
+
+
+
+
+
@@ -1723,7 +1975,9 @@ f "2" = 2
&phases;
-
+
+ &shared_libs;
+
Using Concurrent HaskellConcurrent Haskellusing
@@ -1732,7 +1986,7 @@ f "2" = 2
special option or libraries compiled in a certain way. To get access to
the support libraries for Concurrent Haskell, just import
Control.Concurrent. More information on Concurrent Haskell is provided in the documentation for that module.
+ url="&libraryBaseLocation;/Control-Concurrent.html">Control.Concurrent. More information on Concurrent Haskell is provided in the documentation for that module.
The following RTS option(s) affect the behaviour of Concurrent
Haskell programs:RTS options, concurrent
@@ -1862,6 +2116,10 @@ f "2" = 2
There is no means (currently) by which this value
may vary after the program has started.
+
+ The current value of the option
+ is available to the Haskell program
+ via GHC.Conc.numCapabilities.
@@ -1871,35 +2129,34 @@ f "2" = 2
-
- RTS
+
+ RTS
option
- Disable automatic migration for load balancing.
- Normally the runtime will automatically try to schedule
- threads across the available CPUs to make use of idle
- CPUs; this option disables that behaviour. It is probably
- only of use if you are explicitly scheduling threads onto
- CPUs with GHC.Conc.forkOnIO.
+ Use the OS's affinity facilities to try to pin OS
+ threads to CPU cores. This is an experimental feature,
+ and may or may not be useful. Please let us know
+ whether it helps for you!
-
- RTS
+
+ RTS
option
- Migrate a thread to the current CPU when it is woken
- up. Normally when a thread is woken up after being
- blocked it will be scheduled on the CPU it was running on
- last; this option allows the thread to immediately migrate
- to the CPU that unblocked it.
-
- The rationale for allowing this eager migration is
- that it tends to move threads that are communicating with
- each other onto the same CPU; however there are
- pathalogical situations where it turns out to be a poor
- strategy. Depending on the communication pattern in your
- program, it may or may not be a good idea.
+ Disable automatic migration for load balancing.
+ Normally the runtime will automatically try to schedule
+ threads across the available CPUs to make use of idle
+ CPUs; this option disables that behaviour. Note that
+ migration only applies to threads; sparks created
+ by par are load-balanced separately
+ by work-stealing.
+
+
+ This option is probably only of use for concurrent
+ programs that explicitly schedule threads onto CPUs
+ with GHC.Conc.forkOnIO.
+
@@ -1913,19 +2170,20 @@ f "2" = 2
whether your program got faster by using more CPUs or not. If the user
time is greater than
the elapsed time, then the program used more than one CPU. You should
- also run the program without -N for comparison.
-
- GHC's parallelism support is new and experimental. It may make your
- program go faster, or it might slow it down - either way, we'd be
- interested to hear from you.
-
- One significant limitation with the current implementation is that
- the garbage collector is still single-threaded, and all execution must
- stop when GC takes place. This can be a significant bottleneck in a
- parallel program, especially if your program does a lot of GC. If this
- happens to you, then try reducing the cost of GC by tweaking the GC
- settings (): enlarging the heap or the
- allocation area size is a good start.
+ also run the program without -N for
+ comparison.
+
+ The output of +RTS -s tells you how
+ many “sparks” were created and executed during the
+ run of the program (see ), which
+ will give you an idea how well your par
+ annotations are working.
+
+ GHC's parallelism support has improved in 6.12.1 as a
+ result of much experimentation and tuning in the runtime
+ system. We'd still be interested to hear how well it works
+ for you, and we're also interested in collecting parallel
+ programs to add to our benchmarking suite.
@@ -1942,26 +2200,23 @@ f "2" = 2
- :
+ :
- (iX86 machines)-monly-N-regs
- option (iX86 only) GHC tries to
- “steal” four registers from GCC, for performance
- reasons; it almost always works. However, when GCC is
- compiling some modules with four stolen registers, it will
- crash, probably saying:
-
-
-Foo.hc:533: fixed or forbidden register was spilled.
-This may be due to a compiler bug or to impossible asm
-statements or clauses.
-
-
- Just give some registers back with
- . Try `3' first, then `2'.
- If `2' doesn't work, please report the bug to us.
-
+
+ (x86 only, added in GHC 7.0.1) Use the SSE2 registers and
+ instruction set to implement floating point operations
+ when using the native code generator. This gives a
+ substantial performance improvement for floating point,
+ but the resulting compiled code will only run on
+ processors that support SSE2 (Intel Pentium 4 and later,
+ or AMD Athlon 64 and later).
+
+
+ SSE2 is unconditionally used on x86-64 platforms.
+
+
+
@@ -1975,12 +2230,11 @@ statements or clauses.
GHC can dump its optimized intermediate code (said to be in “Core” format)
to a file as a side-effect of compilation. Non-GHC back-end tools can read and process Core files; these files have the suffix
- .hcr. The Core format is described in
+ .hcr. The Core format is described in An External Representation for the GHC Core Language,
and sample tools
- for manipulating Core files (in Haskell) are in the GHC source distribution
- directory under utils/ext-core.
- Note that the format of .hcr
+ for manipulating Core files (in Haskell) are available in the
+ extcore package on Hackage. Note that the format of .hcr
files is different from the Core output format that GHC generates
for debugging purposes (), though the two formats appear somewhat similar.
@@ -2013,7 +2267,6 @@ statements or clauses.