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Update documentation around non-capturing monadic bind for Action #849

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Update documentation around non-capturing monadic bind for Action #849

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10 changes: 8 additions & 2 deletions src/Development/Shake/Internal/Core/Types.hs
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Expand Up @@ -60,8 +60,14 @@ import Prelude
-- To raise an exception call 'error', 'fail' or @'liftIO' . 'throwIO'@.
--
-- The 'Action' type is both a 'Monad' and 'Applicative'. Anything that is depended upon applicatively
-- will have its dependencies run in parallel. For example @'need' [\"a\"] *> 'need [\"b\"]@ is equivalent
-- to @'need' [\"a\", \"b\"]@.
-- will have its dependencies run in parallel. For example,
-- @'Development.Shake.Internal.Rules.File.need' [\"a\"] '*>' 'Development.Shake.Internal.Rules.File.need' [\"b\"]@
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I needed to fully qualify the path to need here, since it appears that Haddock can't figure it out:

https://hackage.haskell.org/package/shake-0.19.8/docs/Development-Shake.html#t:Action

image

See how the needs on the last line here aren't actually links, since Haddock doesn't seem to know where it should link to? Writing these as fully-qualified references should fix this.

-- is equivalent to @'need' [\"a\", \"b\"]@.
--
-- Note that since Shake 0.18, the non-capturing monadic bind ('>>') will also run its dependencies in parallel.
-- For example,
-- @'Development.Shake.Internal.Rules.File.need' [\"a\"] '>>' 'Development.Shake.Internal.Rules.File.need' [\"b\"]@
-- is also equivalent to @'Development.Shake.Internal.Rules.File.need' [\"a\", \"b\"]@.
newtype Action a = Action {fromAction :: RAW ([String],[Key]) [Value] Global Local a}
deriving (Functor, Applicative, Monad, MonadIO, Typeable, Semigroup, Monoid, MonadFail)

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9 changes: 7 additions & 2 deletions src/Development/Shake/Internal/Rules/File.hs
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Expand Up @@ -371,8 +371,13 @@ fileForward help act = addUserRule $ FileRule help $ fmap ModeForward . act
-- 'Development.Shake.cmd' \"rot13\" [src] \"-o\" [out]
-- @
--
-- Usually @need [foo,bar]@ is preferable to @need [foo] >> need [bar]@ as the former allows greater
-- parallelism, while the latter requires @foo@ to finish building before starting to build @bar@.
-- Note that the following expressions are all equivalent. @foo@ and @bar@ are built in parallel:
--
-- - @need [foo,bar]@
-- - @need [foo] '*>' need [bar]@
-- - @need [foo] '>>' need [bar]@
--
-- In this situation, @need [foo, bar]@ is preferable, since the parallelism is the most obvious.
Comment on lines -374 to +380
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I had also wanted to add a note here saying something like:

If you do require that two separate needs are built sequentially, you can put another (non-need) Action in between, like the following:

do
  need [foo]
  liftIO (putStr "")
  need [bar]

However:

  • I wasn't sure what would be the best way to write this "no-op" Action (liftIO putStr seems kind of hacky)
  • This isn't something that just affects need, it also affects all the other actions that use need internally, like readFileLines.

--
-- This function should not be called with wildcards (e.g. @*.txt@ - use 'getDirectoryFiles' to expand them),
-- environment variables (e.g. @$HOME@ - use 'getEnv' to expand them) or directories (directories cannot be
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