shake-0.10.6: Build system library, like Make, but more accurate dependencies.

Safe HaskellNone




This module is used for defining Shake build systems. As a simple example of a Shake build system, let us build the file result.tar from the files listed by result.txt:

import Development.Shake
import Development.Shake.FilePath

main = shakeArgs shakeOptions $ do
    want ["result.tar"]
    "*.tar" *> \out -> do
        contents <- readFileLines $ out -<.> "txt"
        need contents
        cmd "tar -cf" [out] contents

We start by importing the modules defining both Shake and routines for manipulating FilePath values. We define main to call shake with the default shakeOptions. As the second argument to shake, we provide a set of rules. There are two common forms of rules, want to specify target files, and *> to define a rule which builds a FilePattern. We use want to require that after the build completes the file result.tar should be ready.

The *.tar rule describes how to build files with the extension .tar, including result.tar. We readFileLines on result.txt, after changing the .tar extension to .txt. We read each line into the variable contents -- being a list of the files that should go into result.tar. Next, we depend (need) all the files in contents. If any of these files change, the rule will be repeated. Finally we call the tar program. If either result.txt changes, or any of the files listed by result.txt change, then result.tar will be rebuilt.

When writing a Shake build system, start by defining what you want, then write rules with *> to produce the results. Before calling cmd you should ensure that any files the command requires are demanded with calls to need. We offer the following advice to Shake users:

  • If ghc --make or cabal is capable of building your project, use that instead. Custom build systems are necessary for many complex projects, but many projects are not complex.
  • The shakeArgs function automatically handles command line arguments. To define non-file targets use phony.
  • Put all result files in a distinguished directory, for example _make. You can implement a clean command by removing that directory, using removeFilesAfter "_make" ["//*"].
  • To obtain parallel builds set shakeThreads to a number greater than 1. You may also need to compile with -threaded.
  • Lots of compilers produce .o files. To avoid overlapping rules, use .c.o for C compilers, .hs.o for Haskell compilers etc.
  • Do not be afraid to mix Shake rules, system commands and other Haskell libraries -- use each for what it does best.
  • The more accurate the dependencies are, the better. Use additional rules like doesFileExist and getDirectoryFiles to track information other than just the contents of files. For information in the environment that you suspect will change regularly (perhaps ghc version number), either write the information to a file with alwaysRerun and writeFileChanged, or use addOracle.

The theory behind Shake is described in an ICFP 2012 paper, Shake Before Building -- Replacing Make with Haskell The associated talk forms a short overview of Shake

Acknowledgements: Thanks to Austin Seipp for properly integrating the profiling code.



shake :: ShakeOptions -> Rules () -> IO ()Source

Main entry point for running Shake build systems. For an example see the top of the module Development.Shake. Use ShakeOptions to specify how the system runs, and Rules to specify what to build. The function will throw an exception if the build fails.

To use command line flags to modify ShakeOptions see shakeArgs.

type ShakeValue a = (Show a, Typeable a, Eq a, Hashable a, Binary a, NFData a)Source

Define an alias for the six type classes required for things involved in Shake Rules. This alias is only available in GHC 7.4 and above, and requires the ConstraintKinds extension.

To define your own values meeting the necessary constraints it is convenient to use the extensions GeneralizedNewtypeDeriving and DeriveDataTypeable to write:

 newtype MyType = MyType (String, Bool) deriving (Show,Typeable,Eq,Hashable,Binary,NFData)

class (ShakeValue key, ShakeValue value) => Rule key value whereSource

Define a pair of types that can be used by Shake rules. To import all the type classes required see Development.Shake.Classes.


storedValue :: key -> IO (Maybe value)Source

Retrieve the value associated with a key, if available.

As an example for filenames/timestamps, if the file exists you should return Just the timestamp, but otherwise return Nothing. For rules whose values are not stored externally, storedValue should return Nothing.

data Rules a Source

Define a set of rules. Rules can be created with calls to rule, defaultRule or action. Rules are combined with either the Monoid instance, or (more commonly) the Monad instance and do notation.

defaultRule :: Rule key value => (key -> Maybe (Action value)) -> Rules ()Source

Like rule, but lower priority, if no rule exists then defaultRule is checked. All default rules must be disjoint.

rule :: Rule key value => (key -> Maybe (Action value)) -> Rules ()Source

Add a rule to build a key, returning an appropriate Action. All rules must be disjoint. To define lower priority rules use defaultRule.

action :: Action a -> Rules ()Source

Run an action, usually used for specifying top-level requirements.

withoutActions :: Rules () -> Rules ()Source

Remove all actions specified in a set of rules, usually used for implementing command line specification of what to build.

data Action a Source

The Action monad, use liftIO to raise IO actions into it, and need to execute files. Action values are used by rule and action.

apply :: Rule key value => [key] -> Action [value]Source

Execute a rule, returning the associated values. If possible, the rules will be run in parallel. This function requires that appropriate rules have been added with rule or defaultRule.

apply1 :: Rule key value => key -> Action valueSource

Apply a single rule, equivalent to calling apply with a singleton list. Where possible, use apply to allow parallelism.

traced :: String -> IO a -> Action aSource

Write an action to the trace list, along with the start/end time of running the IO action. The cmd and command functions automatically call traced. The trace list is used for profile reports (see shakeReport).

liftIO :: MonadIO m => forall a. IO a -> m a

Lift a computation from the IO monad.

actionOnException :: Action a -> IO b -> Action aSource

If an exception is raised by the Action, perform some IO.

actionFinally :: Action a -> IO b -> Action aSource

After an Action, perform some IO, even if there is an exception.

data ShakeException Source

Error representing all expected exceptions thrown by Shake. Problems when executing rules will be raising using this exception type.




shakeExceptionTarget :: String

The target that was being built when the exception occured.

shakeExceptionStack :: [String]

The stack of targets, where the shakeExceptionTarget is last.

shakeExceptionInner :: SomeException

The underlying exception that was raised.


data ShakeOptions Source

Options to control the execution of Shake, usually specified by overriding fields in shakeOptions:

 shakeOptions{shakeThreads=4, shakeReport=Just "report.html"}

The Data instance for this type reports the shakeProgress and shakeOutput fields as having the abstract type Function, because Data cannot be defined for functions.




shakeFiles :: FilePath

Defaults to .shake. The prefix of the filename used for storing Shake metadata files. All metadata files will be named shakeFiles.extension, for some extension.

shakeThreads :: Int

Defaults to 1. Maximum number of rules to run in parallel, similar to make --jobs=N. To enable parallelism you may need to compile with -threaded. For many build systems, a number equal to or slightly less than the number of physical processors works well.

shakeVersion :: String

Defaults to 1. The version number of your build rules. Change the version number to force a complete rebuild, such as when making significant changes to the rules that require a wipe. The version number should be set in the source code, and not passed on the command line.

shakeVerbosity :: Verbosity

Defaults to Normal. What level of messages should be printed out.

shakeStaunch :: Bool

Defaults to False. Operate in staunch mode, where building continues even after errors, similar to make --keep-going.

shakeReport :: Maybe FilePath

Defaults to Nothing. Write an HTML profiling report to a file, showing which rules rebuilt, why, and how much time they took. Useful for improving the speed of your build systems.

shakeLint :: Bool

Defaults to False. Perform basic sanity checks during building, checking the current directory is not modified and that output files are not modified by multiple rules. These sanity checks do not check for missing or redundant dependencies.

shakeFlush :: Maybe Double

Defaults to Just 10. How often to flush Shake metadata files in seconds, or Nothing to never flush explicitly. It is possible that on abnormal termination (not Haskell exceptions) any rules that completed in the last shakeFlush seconds will be lost.

shakeAssume :: Maybe Assume

Defaults to Nothing. Assume all build objects are clean/dirty, see Assume for details. Can be used to implement make --touch.

shakeAbbreviations :: [(String, String)]

Defaults to []. A list of substrings that should be abbreviated in status messages, and their corresponding abbreviation. Commonly used to replace the long paths (e.g. .make/i586-linux-gcc/output) with an abbreviation (e.g. $OUT).

shakeStorageLog :: Bool

Defaults to False. Write a message to whenever a storage event happens which may impact on the current stored progress. Examples include database version number changes, database compaction or corrupt files.

shakeLineBuffering :: Bool

Defaults to True. Change stdout and stderr to line buffering while running Shake.

shakeTimings :: Bool

Default to False. Print timing information for each stage at the end.

shakeProgress :: IO Progress -> IO ()

Defaults to no action. A function called on a separate thread when the build starts, allowing progress to be reported. For applications that want to display progress messages, progressSimple is often sufficient, but more advanced users should look at the Progress data type.

shakeOutput :: Verbosity -> String -> IO ()

Defaults to writing using putStrLn. A function called to output messages from Shake, along with the Verbosity at which that message should be printed. This function will be called atomically from all other shakeOutput functions. The Verbosity will always be greater than or higher than shakeVerbosity.

data Assume Source

The current assumptions made by the build system, used by shakeAssume. These options allow the end user to specify that any rules run are either to be treated as clean, or as dirty, regardless of what the build system thinks.

These assumptions only operate on files reached by the current action commands. Any other files in the database are left unchanged.



Assume that all rules reached are dirty and require rebuilding, equivalent to storedValue always returning Nothing. Useful to undo the results of AssumeClean, for benchmarking rebuild speed and for rebuilding if untracked dependencies have changed. This assumption is safe, but may cause more rebuilding than necessary.


This assumption is unsafe, and may lead to incorrect build results in this run, and in future runs. Assume and record that all rules reached are clean and do not require rebuilding, provided the rule has a storedValue and has been built before. Useful if you have modified a file in some inconsequential way, such as only the comments or whitespace, and wish to avoid a rebuild.


This assumption is unsafe, and may lead to incorrect build results in this run. Assume that all rules reached are clean in this run. Only useful for benchmarking, to remove any overhead from running storedValue operations.

Command line

shakeArgs :: ShakeOptions -> Rules () -> IO ()Source

Run a build system using command line arguments for configuration. The available flags are those from shakeOptDescrs, along with a few additional make compatible flags that are not represented in ShakeOptions, such as --print-directory. If there are no file arguments then the Rules are used directly, otherwise the file arguments are wanted (after calling withoutActions). As an example:

 main = shakeArgs shakeOptions{shakeFiles = "_make/", shakeProgress = progressSimple} $ do
     phony "clean" $ removeFilesAfter "_make" ["//*"]
     want ["_make/neil.txt","_make/emily.txt"]
     "_make/*.txt" *> \out ->
         ... build action here ...

This build system will default to building neil.txt and emily.txt, while showing progress messages, and putting the Shake files in locations such as _make/.database. Some example command line flags:

  • main --no-progress will turn off progress messages.
  • main -j6 will build on 6 threads.
  • main --help will display a list of supported flags.
  • main clean will not build anything, but will remove the _make directory, including the any shakeFiles.
  • main _make/henry.txt will not build neil.txt or emily.txt, but will instead build henry.txt.

shakeArgsWith :: ShakeOptions -> [OptDescr (Either String a)] -> ([a] -> [String] -> IO (Maybe (Rules ()))) -> IO ()Source

A version of shakeArgs with more flexible handling of command line arguments. The caller of shakeArgsWith can add additional flags (the second argument) and chose how to convert the flags/arguments into rules (the third argument). Given:

 shakeArgsWith opts flags (\flagValues argValues -> result)
  • opts is the initial ShakeOptions value, which may have some fields overriden by command line flags. This argument is usually shakeOptions, perhaps with a few fields overriden.
  • flags is a list of flag descriptions, which either produce a String containing an error message (typically for flags with invalid arguments, .e.g. Left "could not parse as int"), or a value that is passed as flagValues. If you have no custom flags, pass [].
  • flagValues is a list of custom flags that the user supplied. If flags == [] then this list will be [].
  • argValues is a list of non-flag arguments, which are often treated as files and passed to want.
  • result should produce a Nothing to indicate that no building needs to take place, or a Just providing the rules that should be used.

As an example of a build system that can use either gcc or distcc for compiling:

import System.Console.GetOpt

data Flags = DistCC deriving Eq
flags = [Option "" ["distcc"] (NoArg $ Right DistCC) "Run distributed."]

main = shakeArgsWith shakeOptions flags $ \flags targets -> return $ Just $ do
     if null targets then want ["result.exe"] else want targets
     let compiler = if DistCC `elem` flags then "distcc" else "gcc"
     "*.o" *> \out -> do
         need ...
         cmd compiler ...

Now you can pass --distcc to use the distcc compiler.

shakeOptDescrs :: [OptDescr (Either String (ShakeOptions -> ShakeOptions))]Source

A list of command line options that can be used to modify ShakeOptions. Each option returns either an error message (invalid argument to the flag) or a function that changes some fields in ShakeOptions. The command line flags are make compatible where possbile, but additional flags have been added for the extra options Shake supports.

Progress reporting

data Progress Source

Information about the current state of the build, obtained by passing a callback function to shakeProgress. Typically a program will use progressDisplay to poll this value and produce status messages, which is implemented using this data type.




isRunning :: !Bool

Starts out True, becomes False once the build has completed.

isFailure :: !(Maybe String)

Starts out Nothing, becomes Just if a rule fails.

countSkipped :: !Int

Number of rules which were required, but were already in a valid state.

countBuilt :: !Int

Number of rules which were have been built in this run.

countUnknown :: !Int

Number of rules which have been built previously, but are not yet known to be required.

countTodo :: !Int

Number of rules which are currently required (ignoring dependencies that do not change), but not built.

timeSkipped :: !Double

Time spent building countSkipped rules in previous runs.

timeBuilt :: !Double

Time spent building countBuilt rules.

timeUnknown :: !Double

Time spent building countUnknown rules in previous runs.

timeTodo :: !(Double, Int)

Time spent building countTodo rules in previous runs, plus the number which have no known time (have never been built before).

progressSimple :: IO Progress -> IO ()Source

A simple method for displaying progress messages, suitable for using as shakeProgress. This function writes the current progress to the titlebar every five seconds. The function is defined as:

progressSimple = progressDisplay 5 progressTitlebar

progressDisplay :: Double -> (String -> IO ()) -> IO Progress -> IO ()Source

Given a sampling interval (in seconds) and a way to display the status message, produce a function suitable for using as shakeProgress. This function polls the progress information every n seconds, produces a status message and displays it using the display function.

Typical status messages will take the form of 1m25s (15%), indicating that the build is predicted to complete in 1 minute 25 seconds (85 seconds total), and 15% of the necessary build time has elapsed. This function uses past observations to predict future behaviour, and as such, is only guessing. The time is likely to go up as well as down, and will be less accurate from a clean build (as the system has fewer past observations).

The current implementation is to predict the time remaining (based on timeTodo) and the work already done (timeBuilt). The percentage is then calculated as remaining / (done + remaining), while time left is calculated by scaling remaining by the observed work rate in this build, roughly done / time_elapsed.

progressTitlebar :: String -> IO ()Source

Set the title of the current console window to the given text. If the environment variable $TERM is set to xterm this uses xterm escape sequences. On Windows, if not detected as an xterm, this function uses the SetConsoleTitle API.


data Verbosity Source

The verbosity data type, used by shakeVerbosity.



Don't print any messages.


Only print essential messages, typically errors.


Print errors and # command-name file-name when running a traced command.


Print errors and full command lines when running a system' command.


Print errors, full command line and status messages when starting a rule.


Print messages for virtually everything (mostly for debugging).

getVerbosity :: Action VerbositySource

Get the current verbosity level, as set by shakeVerbosity. If you want to output information to the console, you are recommended to use putLoud / putNormal / putQuiet, which ensures multiple messages are not interleaved.

putLoud :: String -> Action ()Source

Write a message to the output when the verbosity (shakeVerbosity) is appropriate. The output will not be interleaved with any other Shake messages (other than those generated by system commands).

putNormal :: String -> Action ()Source

Write a message to the output when the verbosity (shakeVerbosity) is appropriate. The output will not be interleaved with any other Shake messages (other than those generated by system commands).

putQuiet :: String -> Action ()Source

Write a message to the output when the verbosity (shakeVerbosity) is appropriate. The output will not be interleaved with any other Shake messages (other than those generated by system commands).

quietly :: Action a -> Action aSource

Run an action with Quiet verbosity, in particular messages produced by traced (including from cmd or command) will not be printed to the screen.

Running commands

command :: CmdResult r => [CmdOption] -> String -> [String] -> Action rSource

Execute a system command. Before running command make sure you need any files that are required by the command.

This function takes a list of options (often just [], see CmdOption for the available options), the name of the executable (either a full name, or a program on the $PATH) and a list of arguments. The result is often (), but can be a tuple containg any of Stdout, Stderr and Exit. Some examples:

 command_ [] "gcc" ["-c","myfile.c"]                          -- compile a file, throwing an exception on failure
 Exit c <- command [] "gcc" ["-c",myfile]                     -- run a command, recording the exit code
 (Exit c, Stderr err) <- command [] "gcc" ["-c","myfile.c"]   -- run a command, recording the exit code and error output
 Stdout out <- command [] "gcc" ["-MM","myfile.c"]            -- run a command, recording the output
 command_ [Cwd "generated"] "gcc" ["-c",myfile]               -- run a command in a directory

Unless you retrieve the ExitCode using Exit, any ExitFailure will throw an error, including the Stderr in the exception message. If you capture the Stdout or Stderr, that stream will not be echoed to the console, unless you use the option EchoStdout or EchoStderr.

If you use command inside a do block and do not use the result, you may get a compile-time error about being unable to deduce CmdResult. To avoid this error, use command_.

command_ :: [CmdOption] -> String -> [String] -> Action ()Source

A version of command where you do not require any results, used to avoid errors about being unable to deduce CmdResult.

cmd :: CmdArguments args => args :-> Action rSource

A variable arity version of command.

  • String arguments are treated as whitespace separated arguments.
  • [String] arguments are treated as literal arguments.
  • CmdOption arguments are used as options.

To take the examples from command:

 () <- cmd "gcc -c myfile.c"                                  -- compile a file, throwing an exception on failure
 Exit c <- cmd "gcc -c" [myfile]                              -- run a command, recording the exit code
 (Exit c, Stderr err) <- cmd "gcc -c myfile.c"                -- run a command, recording the exit code and error output
 Stdout out <- cmd "gcc -MM myfile.c"                         -- run a command, recording the output
 cmd (Cwd "generated") "gcc -c" [myfile] :: Action ()         -- run a command in a directory

When passing file arguments we use [myfile] so that if the myfile variable contains spaces they are properly escaped.

If you use cmd inside a do block and do not use the result, you may get a compile-time error about being unable to deduce CmdResult. To avoid this error, bind the result to (), or include a type signature.

newtype Stdout Source

Collect the stdout of the process. If you are collecting the stdout, it will not be echoed to the terminal, unless you include EchoStdout.




fromStdout :: String


newtype Stderr Source

Collect the stderr of the process. If you are collecting the stderr, it will not be echoed to the terminal, unless you include EchoStderr.




fromStderr :: String


newtype Exit Source

Collect the ExitCode of the process. If you do not collect the exit code, any ExitFailure will cause an exception.




fromExit :: ExitCode


class CmdResult a Source

A class for specifying what results you want to collect from a process. Values are formed of Stdout, Stderr, Exit and tuples of those.

data CmdOption Source

Options passed to command or cmd to control how processes are executed.


Cwd FilePath

Change the current directory in the spawned process. By default uses this processes current directory.

Env [(String, String)]

Change the environment variables in the spawned process. By default uses this processes environment.

Stdin String

Given as the stdin of the spawned process. By default no stdin is given.


Pass the command to the shell without escaping - any arguments will be joined with spaces. By default arguments are escaped properly.


Treat the stdin/stdout/stderr messages as binary. By default streams use text encoding.

Traced String

Name to use with traced, or "" for no tracing. By default traces using the name of the executable.

WithStderr Bool

Should I include the stderr in the exception if the command fails? Defaults to True.

EchoStdout Bool

Should I echo the stdout? Defaults to True unless a Stdout result is required.

EchoStderr Bool

Should I echo the stderr? Defaults to True unless a Stderr result is required.

Utility functions

system' :: FilePath -> [String] -> Action ()Source

Execute a system command. This function will raise an error if the exit code is non-zero. Before running system' make sure you need any required files.

systemCwd :: FilePath -> FilePath -> [String] -> Action ()Source

Deprecated: Please use command or cmd instead, with Cwd. This function will be removed in a future version.

Execute a system command with a specified current working directory (first argument). This function will raise an error if the exit code is non-zero. Before running systemCwd make sure you need any required files.

 systemCwd "/usr/MyDirectory" "pwd" []

systemOutput :: FilePath -> [String] -> Action (String, String)Source

Deprecated: Please use command or cmd instead, with Stdout or Stderr. This function will be removed in a future version.

Execute a system command, returning (stdout,stderr). This function will raise an error if the exit code is non-zero. Before running systemOutput make sure you need any required files.

copyFile' :: FilePath -> FilePath -> Action ()Source

copyFile' old new copies the existing file from old to new. The old file is has need called on it before copying the file.

readFile' :: FilePath -> Action StringSource

Read a file, after calling need.

readFileLines :: FilePath -> Action [String]Source

A version of readFile' which also splits the result into lines.

writeFile' :: FilePath -> String -> Action ()Source

Write a file, lifted to the Action monad.

writeFileLines :: FilePath -> [String] -> Action ()Source

A version of writeFile' which writes out a list of lines.

writeFileChanged :: FilePath -> String -> Action ()Source

Write a file, but only if the contents would change.

removeFiles :: FilePath -> [FilePattern] -> IO ()Source

Remove all empty directories and files that match any of the patterns beneath a directory. Some examples:

 removeFiles "output" ["//*"]
 removeFiles "." ["//*.hi","//*.o"]

This function is often useful when writing a clean action for your build system, often as a phony rule.

removeFilesAfter :: FilePath -> [FilePattern] -> Action ()Source

Remove files, like removeFiles, but executed after the build completes successfully. Useful for implementing clean actions that delete files Shake may have open for building.

File rules

need :: [FilePath] -> Action ()Source

Require that the following files are built before continuing. Particularly necessary when calling cmd or command. As an example:

 "//*.rot13" *> \out -> do
     let src = dropExtension out
     need [src]
     cmd "rot13" [src] "-o" [out]

want :: [FilePath] -> Rules ()Source

Require that the following are built by the rules, used to specify the target.

 main = shake shakeOptions $ do
    want ["Main.exe"]

This program will build Main.exe, given sufficient rules.

(*>) :: FilePattern -> (FilePath -> Action ()) -> Rules ()Source

Define a rule that matches a FilePattern. No file required by the system must be matched by more than one pattern. For the pattern rules, see ?==.

 "*.asm.o" *> \out -> do
     let src = dropExtension out
     need [src]
     cmd "as" [src] "-o" [out]

To define a build system for multiple compiled languages, we recommend using .asm.o, .cpp.o, .hs.o, to indicate which language produces an object file. I.e., the file foo.cpp produces object file foo.cpp.o.

Note that matching is case-sensitive, even on Windows.

(**>) :: [FilePattern] -> (FilePath -> Action ()) -> Rules ()Source

Define a set of patterns, and if any of them match, run the associated rule. See *>.

(?>) :: (FilePath -> Bool) -> (FilePath -> Action ()) -> Rules ()Source

Define a rule to build files. If the first argument returns True for a given file, the second argument will be used to build it. Usually *> is sufficient, but ?> gives additional power. For any file used by the build system, only one rule should return True.

 (all isUpper . takeBaseName) ?> \out -> do
     let src = replaceBaseName out $ map toLower $ takeBaseName out
     writeFile' out . map toUpper =<< readFile' src

phony :: String -> Action () -> Rules ()Source

Declare a phony action, this is an action that does not produce a file, and will be rerun in every execution that requires it. You can demand phony rules using want / need.

Phony actions are intended to define command-line abbreviations. You should not need phony actions as dependencies of rules, as that will cause excessive rebuilding.

(?>>) :: (FilePath -> Maybe [FilePath]) -> ([FilePath] -> Action ()) -> Rules ()Source

Define a rule for building multiple files at the same time, a more powerful and more dangerous version of *>>.

Given an application test ?>> ..., test should return Just if the rule applies, and should return the list of files that will be produced. This list must include the file passed as an argument and should obey the invariant:

 forAll $ \x ys -> test x == Just ys ==> x `elem` ys && all ((== Just ys) . test) ys

As an example of a function satisfying the invariaint:

test x | takeExtension x `elem` [".hi",".o"]
        = Just [dropExtension x <.> "hi", dropExtension x <.> "o"]
test _ = Nothing

Regardless of whether Foo.hi or Foo.o is passed, the function always returns [Foo.hi, Foo.o].

(*>>) :: [FilePattern] -> ([FilePath] -> Action ()) -> Rules ()Source

Define a rule for building multiple files at the same time. As an example, a single invokation of GHC produces both .hi and .o files:

 ["*.o","*.hi"] *>> \[o,hi] -> do
     let hs = o -<.> "hs"
     need ... -- all files the .hs import
     cmd "ghc -c" [hs]

However, in practice, it's usually easier to define rules with *> and make the .hi depend on the .o. When defining rules that build multiple files, all the FilePattern values must have the same sequence of // and * wildcards in the same order.

type FilePattern = StringSource

A type synonym for file patterns, containing // and *. For the syntax and semantics of FilePattern see ?==.

(?==) :: FilePattern -> FilePath -> BoolSource

Match a FilePattern against a FilePath, There are only two special forms:

  • * matches an entire path component, excluding any separators.
  • // matches an arbitrary number of path components.

Some examples that match:

 "//*.c" ?== "foo/bar/baz.c"
 "*.c" ?== "baz.c"
 "//*.c" ?== "baz.c"
 "test.c" ?== "test.c"

Examples that don't match:

 "*.c" ?== "foo/bar.c"
 "*/*.c" ?== "foo/bar/baz.c"

An example that only matches on Windows:

 "foo/bar" ?== "foo\\bar"

Directory rules

doesFileExist :: FilePath -> Action BoolSource

Returns True if the file exists.

doesDirectoryExist :: FilePath -> Action BoolSource

Returns True if the directory exists.

getDirectoryContents :: FilePath -> Action [FilePath]Source

Get the contents of a directory. The result will be sorted, and will not contain the entries . or .. (unlike the standard Haskell version). The resulting paths will be relative to the first argument.

It is usually simpler to call either getDirectoryFiles or getDirectoryDirs.

getDirectoryFiles :: FilePath -> [FilePattern] -> Action [FilePath]Source

Get the files anywhere under a directory that match any of a set of patterns. For the interpretation of the patterns see ?==. All results will be relative to the FilePath argument. Some examples:

 getDirectoryFiles "Config" ["//*.xml"]
     -- All .xml files anywhere under the Config directory
     -- If Config/foo/bar.xml exists it will return ["foo/bar.xml"]
 getDirectoryFiles "Modules" ["*.hs","*.lhs"]
     -- All .hs or .lhs in the Modules directory
     -- If Modules/foo.hs and Modules/foo.lhs exist, it will return ["foo.hs","foo.lhs"]

If you require a qualified file name it is often easier to use "" as FilePath argument, for example the following two expressions are equivalent:

 fmap (map ("Config" </>)) (getDirectoryFiles "Config" ["//*.xml"])
 getDirectoryFiles "" ["Config//*.xml"]

getDirectoryDirs :: FilePath -> Action [FilePath]Source

Get the directories in a directory, not including . or ... All directories are relative to the argument directory.

 getDirectoryDirs "/Users"
    -- Return all directories in the /Users directory
    -- e.g. ["Emily","Henry","Neil"]

Environment rules

getEnv :: String -> Action (Maybe String)Source

Return Just the value of the environment variable, or Nothing if the variable is not set.

Oracle rules

addOracle :: (ShakeValue q, ShakeValue a) => (q -> Action a) -> Rules (q -> Action a)Source

Add extra information which rules can depend on. An oracle is a function from a question type q, to an answer type a. As an example, we can define an oracle allowing you to depend on the current version of GHC:

 newtype GhcVersion = GhcVersion () deriving (Show,Typeable,Eq,Hashable,Binary,NFData)
 rules = do
     addOracle $ \(GhcVersion _) -> fmap (last . words . fromStdout) $ cmd "ghc --version"
     ... rules ...

If a rule calls askOracle (GhcVersion ()), that rule will be rerun whenever the GHC version changes. Some notes:

  • We define GhcVersion with a newtype around (), allowing the use of GeneralizedNewtypeDeriving. All the necessary type classes are exported from Development.Shake.Classes.
  • Each call to addOracle must use a different type of question.
  • Actions passed to addOracle will be run in every build they are required, but if their value does not change they will not invalidate any rules depending on them. To get a similar behaviour using data stored in files, see alwaysRerun.
  • If the value returned by askOracle is ignored then askOracleWith may help avoid ambiguous type messages. Alternatively, use the result of addOracle, which is askOracle restricted to the correct type.

As a more complex example, consider tracking Haskell package versions:

newtype GhcPkgList = GhcPkgList () deriving (Show,Typeable,Eq,Hashable,Binary,NFData)
newtype GhcPkgVersion = GhcPkgVersion String deriving (Show,Typeable,Eq,Hashable,Binary,NFData)

rules = do
    getPkgList <- addOracle $ \GhcPkgList{} -> do
        Stdout out <- cmd "ghc-pkg list --simple-output"
        return [(reverse b, reverse a) | x <- words out, let (a,_:b) = break (== '-') $ reverse x]
    getPkgVersion <- addOracle $ \(GhcPkgVersion pkg) -> do
        pkgs <- getPkgList $ GhcPkgList ()
        return $ lookup pkg pkgs
    "myrule" *> \_ -> do
        getPkgVersion $ GhcPkgVersion "shake"
        ... rule using the shake version ...

Using these definitions, any rule depending on the version of shake should call getPkgVersion $ GhcPkgVersion "shake" to rebuild when shake is upgraded.

askOracle :: (ShakeValue q, ShakeValue a) => q -> Action aSource

Get information previously added with addOracle. The question/answer types must match those provided to addOracle.

askOracleWith :: (ShakeValue q, ShakeValue a) => q -> a -> Action aSource

Get information previously added with addOracle. The second argument is not used, but can be useful to fix the answer type, avoiding ambiguous type error messages.

Special rules

alwaysRerun :: Action ()Source

Always rerun the associated action. Useful for defining rules that query the environment. For example:

 "ghcVersion.txt" *> \out -> do
     Stdout stdout <- cmd "ghc --version"
     writeFileChanged out stdout

Finite resources

data Resource Source

A type representing a finite resource, which multiple build actions should respect. Created with newResource and used with withResource when defining rules.

As an example, only one set of calls to the Excel API can occur at one time, therefore Excel is a finite resource of quantity 1. You can write:

 shake shakeOptions{shakeThreads=2} $ do
    want ["a.xls","b.xls"]
    excel <- newResource "Excel" 1
    "*.xls" *> \out ->
        withResource excel 1 $
            cmd "excel" out ...

Now the two calls to excel will not happen in parallel. Using Resource is better than MVar as it will not block any other threads from executing. Be careful that the actions run within withResource do not themselves require further quantities of this resource, or you may get a "thread blocked indefinitely in an MVar operation" exception. Typically only system commands (such as cmd) should be run inside withResource, not commands such as need. If an action requires multiple resources, use withResources to avoid deadlock.

As another example, calls to compilers are usually CPU bound but calls to linkers are usually disk bound. Running 8 linkers will often cause an 8 CPU system to grid to a halt. We can limit ourselves to 4 linkers with:

 disk <- newResource "Disk" 4
 want [show i <.> "exe" | i <- [1..100]]
 "*.exe" *> \out ->
     withResource disk 1 $
         cmd "ld -o" [out] ...
 "*.o" *> \out ->
     cmd "cl -o" [out] ...

newResource :: String -> Int -> Rules ResourceSource

Create a new finite resource, given a name (for error messages) and a quantity of the resource that exists. For an example see Resource.

newResourceIO :: String -> Int -> IO ResourceSource

A version of newResource that runs in IO, and can be called before calling shake. Most people should use newResource instead.

withResource :: Resource -> Int -> Action a -> Action aSource

Run an action which uses part of a finite resource. For an example see Resource.

withResources :: [(Resource, Int)] -> Action a -> Action aSource

Run an action which uses part of several finite resources. Acquires the resources in a stable order, to prevent deadlock. If all rules requiring more than one resource acquire those resources with a single call to withResources, resources will not deadlock.

Cached file contents

newCache :: (FilePath -> IO a) -> Rules (FilePath -> Action a)Source

Given a way of loading information from a file, produce a cached version that will load each file at most once. Using the cached function will still result in a dependency on the original file. The argument function should not access any files other than the one passed as its argument. Each call to newCache creates a separate cache that is independent of all other calls to newCache.

This function is useful when creating files that store intermediate values, to avoid the overhead of repeatedly reading from disk, particularly if the file requires expensive parsing. As an example:

 digits <- newCache $ \file -> do
     src <- readFile file
     return $ length $ filter isDigit src
 "*.digits" *> \x -> do
     v1 <- digits (dropExtension x)
     v2 <- digits (dropExtension x)
     writeFile' x $ show (v1,v2)

To create the result MyFile.txt.digits the file MyFile.txt will be read and counted, but only at most once per execution.

newCacheIO :: (FilePath -> IO a) -> IO (FilePath -> Action a)Source

A version of newCache that runs in IO, and can be called before calling shake. Most people should use newCache instead.