RIO

Custom Prelude

One of the core features of rio is that it can be used as a Prelude replacement. Therefore it is best to disable the default Prelude with: NoImplicitPrelude pragma:

{-# LANGUAGE NoImplicitPrelude #-}
import RIO

module RIO.Prelude

module RIO.Prelude.Types

The RIO Monad

newtype RIO env a

The Reader+IO monad. This is different from a ReaderT because:

• It's not a transformer, it hardcodes IO for simpler usage and error messages.
• Instances of typeclasses like MonadLogger are implemented using classes defined on the environment, instead of using an underlying monad.

Constructors

RIO

Fields

• unRIO :: ReaderT env IO a

Instances

(Monoid w, HasWriteRef w env) => MonadWriter w (RIO env)

Defined in RIO.Prelude.RIO

Methods

writer :: (a, w) -> RIO env a

tell :: w -> RIO env ()

listen :: RIO env a -> RIO env (a, w)

pass :: RIO env (a, w -> w) -> RIO env a

HasStateRef s env => MonadState s (RIO env)

Defined in RIO.Prelude.RIO

Methods

get :: RIO env s

put :: s -> RIO env ()

state :: (s -> (a, s)) -> RIO env a

MonadReader env (RIO env)

Defined in RIO.Prelude.RIO

Methods

ask :: RIO env env

local :: (env -> env) -> RIO env a -> RIO env a

reader :: (env -> a) -> RIO env a

Monad (RIO env)

Defined in RIO.Prelude.RIO

Methods

(>>=) :: RIO env a -> (a -> RIO env b) -> RIO env b

(>>) :: RIO env a -> RIO env b -> RIO env b

return :: a -> RIO env a

fail :: String -> RIO env a

Functor (RIO env)

Defined in RIO.Prelude.RIO

Methods

fmap :: (a -> b) -> RIO env a -> RIO env b

(<$) :: a -> RIO env b -> RIO env a

Applicative (RIO env)

Defined in RIO.Prelude.RIO

Methods

pure :: a -> RIO env a

(<*>) :: RIO env (a -> b) -> RIO env a -> RIO env b

liftA2 :: (a -> b -> c) -> RIO env a -> RIO env b -> RIO env c

(*>) :: RIO env a -> RIO env b -> RIO env b

(<*) :: RIO env a -> RIO env b -> RIO env a

MonadIO (RIO env)

Defined in RIO.Prelude.RIO

Methods

liftIO :: IO a -> RIO env a

MonadThrow (RIO env)

Defined in RIO.Prelude.RIO

Methods

throwM :: Exception e => e -> RIO env a

PrimMonad (RIO env)

Defined in RIO.Prelude.RIO

Associated Types

type PrimState (RIO env) :: Type

Methods

primitive :: (State# (PrimState (RIO env)) -> (#State# (PrimState (RIO env)), a#)) -> RIO env a

MonadUnliftIO (RIO env)

Defined in RIO.Prelude.RIO

Methods

askUnliftIO :: RIO env (UnliftIO (RIO env))

withRunInIO :: ((forall a. RIO env a -> IO a) -> IO b) -> RIO env b

Semigroup a => Semigroup (RIO env a)

Defined in RIO.Prelude.RIO

Methods

(<>) :: RIO env a -> RIO env a -> RIO env a

sconcat :: NonEmpty (RIO env a) -> RIO env a

stimes :: Integral b => b -> RIO env a -> RIO env a

Monoid a => Monoid (RIO env a)

Defined in RIO.Prelude.RIO

Methods

mempty :: RIO env a

mappend :: RIO env a -> RIO env a -> RIO env a

mconcat :: [RIO env a] -> RIO env a

type PrimState (RIO env)

Defined in RIO.Prelude.RIO

type PrimState (RIO env) = PrimState IO

runRIO :: MonadIO m => env -> RIO env a -> m a

Using the environment run in IO the action that requires that environment.

Since: 0.0.1.0

liftRIO :: (MonadIO m, MonadReader env m) => RIO env a -> m a

Abstract RIO to an arbitrary MonadReader instance, which can handle IO.

Since: 0.0.1.0

SimpleApp

If all you need is just some default environment that does basic logging and allows spawning processes, then you can use SimpleApp:

{-# LANGUAGE OverloadedStrings #-}
module Main where

main :: IO ()
main =
  runSimpleApp $ do
    logInfo "Hello World!"

Note the OverloadedStrings extension, which is enabled to simplify logging.

module RIO.Prelude.Simple

MonadIO and MonadUnliftIO

module Control.Monad.IO.Unlift

Logger

Running with logging

withLogFunc :: MonadUnliftIO m => LogOptions -> (LogFunc -> m a) -> m a

Given a LogOptions value, run the given function with the specified LogFunc. A common way to use this function is:

let isVerbose = False -- get from the command line instead
logOptions' <- logOptionsHandle stderr isVerbose
let logOptions = setLogUseTime True logOptions'
withLogFunc logOptions $ \lf -> do
  let app = App -- application specific environment
        { appLogFunc = lf
        , appOtherStuff = ...
        }
  runRIO app $ do
    logInfo "Starting app"
    myApp

Since: 0.0.0.0

newLogFunc :: (MonadIO n, MonadIO m) => LogOptions -> n (LogFunc, m ())

Given a LogOptions value, returns both a new LogFunc and a sub-routine that disposes it.

Intended for use if you want to deal with the teardown of LogFunc yourself, otherwise prefer the withLogFunc function instead.

Since: 0.1.3.0

data LogFunc

A logging function, wrapped in a newtype for better error messages.

An implementation may choose any behavior of this value it wishes, including printing to standard output or no action at all.

Since: 0.0.0.0

Instances

Semigroup LogFunc

Perform both sets of actions per log entry.

Since: 0.0.0.0

Defined in RIO.Prelude.Logger

Methods

(<>) :: LogFunc -> LogFunc -> LogFunc

sconcat :: NonEmpty LogFunc -> LogFunc

stimes :: Integral b => b -> LogFunc -> LogFunc

Monoid LogFunc

mempty peforms no logging.

Since: 0.0.0.0

Defined in RIO.Prelude.Logger

Methods

mempty :: LogFunc

mappend :: LogFunc -> LogFunc -> LogFunc

mconcat :: [LogFunc] -> LogFunc

HasLogFunc LogFunc

Defined in RIO.Prelude.Logger

Methods

logFuncL :: Lens' LogFunc LogFunc

class HasLogFunc env where

Environment values with a logging function.

Since: 0.0.0.0

Methods

logFuncL :: Lens' env LogFunc

Instances

HasLogFunc LogFunc

Defined in RIO.Prelude.Logger

Methods

logFuncL :: Lens' LogFunc LogFunc

HasLogFunc LoggedProcessContext

Defined in RIO.Process

Methods

logFuncL :: Lens' LoggedProcessContext LogFunc

HasLogFunc SimpleApp

Defined in RIO.Prelude.Simple

Methods

logFuncL :: Lens' SimpleApp LogFunc

logOptionsHandle

Arguments

:: MonadIO m

=> Handle

-> Bool

Verbose Flag

-> m LogOptions

Create a LogOptions value from the given Handle and whether to perform verbose logging or not. Individiual settings can be overridden using appropriate set functions.

When Verbose Flag is True, the following happens:

• setLogVerboseFormat is called with True
• setLogUseColor is called with True (except on Windows)
• setLogUseLoc is called with True
• setLogUseTime is called with True
• setLogMinLevel is called with Debug log level

Since: 0.0.0.0

Log options

data LogOptions

Configuration for how to create a LogFunc. Intended to be used with the withLogFunc function.

Since: 0.0.0.0

setLogMinLevel :: LogLevel -> LogOptions -> LogOptions

Set the minimum log level. Messages below this level will not be printed.

Default: in verbose mode, LevelDebug. Otherwise, LevelInfo.

Since: 0.0.0.0

setLogMinLevelIO :: IO LogLevel -> LogOptions -> LogOptions

Refer to setLogMinLevel. This modifier allows to alter the verbose format value dynamically at runtime.

Default: in verbose mode, LevelDebug. Otherwise, LevelInfo.

Since: 0.1.3.0

setLogVerboseFormat :: Bool -> LogOptions -> LogOptions

Use the verbose format for printing log messages.

Default: follows the value of the verbose flag.

Since: 0.0.0.0

setLogVerboseFormatIO :: IO Bool -> LogOptions -> LogOptions

Refer to setLogVerboseFormat. This modifier allows to alter the verbose format value dynamically at runtime.

Default: follows the value of the verbose flag.

Since: 0.1.3.0

setLogTerminal :: Bool -> LogOptions -> LogOptions

Do we treat output as a terminal. If True, we will enabled sticky logging functionality.

Default: checks if the Handle provided to logOptionsHandle is a terminal with hIsTerminalDevice.

Since: 0.0.0.0

setLogUseTime :: Bool -> LogOptions -> LogOptions

Include the time when printing log messages.

Default: True in debug mode, False otherwise.

Since: 0.0.0.0

setLogUseColor :: Bool -> LogOptions -> LogOptions

Use ANSI color codes in the log output.

Default: True if in verbose mode and the Handle is a terminal device.

Since: 0.0.0.0

setLogUseLoc :: Bool -> LogOptions -> LogOptions

Use code location in the log output.

Default: True if in verbose mode, False otherwise.

Since: 0.1.2.0

Standard logging functions

logDebug :: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack) => Utf8Builder -> m ()

Log a debug level message with no source.

Since: 0.0.0.0

logInfo :: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack) => Utf8Builder -> m ()

Log an info level message with no source.

Since: 0.0.0.0

logWarn :: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack) => Utf8Builder -> m ()

Log a warn level message with no source.

Since: 0.0.0.0

logError :: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack) => Utf8Builder -> m ()

Log an error level message with no source.

Since: 0.0.0.0

logOther

Arguments

:: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack)

=> Text

level

-> Utf8Builder

-> m ()

Log a message with the specified textual level and no source.

Since: 0.0.0.0

Advanced logging functions

Sticky logging

logSticky :: (MonadIO m, HasCallStack, MonadReader env m, HasLogFunc env) => Utf8Builder -> m ()

Write a "sticky" line to the terminal. Any subsequent lines will overwrite this one, and that same line will be repeated below again. In other words, the line sticks at the bottom of the output forever. Running this function again will replace the sticky line with a new sticky line. When you want to get rid of the sticky line, run logStickyDone.

Note that not all LogFunc implementations will support sticky messages as described. However, the withLogFunc implementation provided by this module does.

Since: 0.0.0.0

logStickyDone :: (MonadIO m, HasCallStack, MonadReader env m, HasLogFunc env) => Utf8Builder -> m ()

This will print out the given message with a newline and disable any further stickiness of the line until a new call to logSticky happens.

Since: 0.0.0.0

With source

logDebugS :: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack) => LogSource -> Utf8Builder -> m ()

Log a debug level message with the given source.

Since: 0.0.0.0

logInfoS :: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack) => LogSource -> Utf8Builder -> m ()

Log an info level message with the given source.

Since: 0.0.0.0

logWarnS :: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack) => LogSource -> Utf8Builder -> m ()

Log a warn level message with the given source.

Since: 0.0.0.0

logErrorS :: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack) => LogSource -> Utf8Builder -> m ()

Log an error level message with the given source.

Since: 0.0.0.0

logOtherS

Arguments

:: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack)

=> Text

level

-> LogSource

-> Utf8Builder

-> m ()

Log a message with the specified textual level and the given source.

Since: 0.0.0.0

Generic log function

logGeneric :: (MonadIO m, MonadReader env m, HasLogFunc env, HasCallStack) => LogSource -> LogLevel -> Utf8Builder -> m ()

Generic, basic function for creating other logging functions.

Since: 0.0.0.0

Advanced running functions

mkLogFunc :: (CallStack -> LogSource -> LogLevel -> Utf8Builder -> IO ()) -> LogFunc

Create a LogFunc from the given function.

Since: 0.0.0.0

logOptionsMemory :: MonadIO m => m (IORef Builder, LogOptions)

Create a LogOptions value which will store its data in memory. This is primarily intended for testing purposes. This will return both a LogOptions value and an IORef containing the resulting Builder value.

This will default to non-verbose settings and assume there is a terminal attached. These assumptions can be overridden using the appropriate set functions.

Since: 0.0.0.0

Data types

data LogLevel

The log level of a message.

Since: 0.0.0.0

Constructors

LevelDebug

LevelInfo

LevelWarn

LevelError

LevelOther !Text

Instances

Eq LogLevel

Defined in RIO.Prelude.Logger

Methods

(==) :: LogLevel -> LogLevel -> Bool

(/=) :: LogLevel -> LogLevel -> Bool

Ord LogLevel

Defined in RIO.Prelude.Logger

Methods

compare :: LogLevel -> LogLevel -> Ordering

(<) :: LogLevel -> LogLevel -> Bool

(<=) :: LogLevel -> LogLevel -> Bool

(>) :: LogLevel -> LogLevel -> Bool

(>=) :: LogLevel -> LogLevel -> Bool

max :: LogLevel -> LogLevel -> LogLevel

min :: LogLevel -> LogLevel -> LogLevel

Read LogLevel

Defined in RIO.Prelude.Logger

Methods

readsPrec :: Int -> ReadS LogLevel

readList :: ReadS [LogLevel]

readPrec :: ReadPrec LogLevel

readListPrec :: ReadPrec [LogLevel]

Show LogLevel

Defined in RIO.Prelude.Logger

Methods

showsPrec :: Int -> LogLevel -> ShowS

show :: LogLevel -> String

showList :: [LogLevel] -> ShowS

type LogSource = Text

Where in the application a log message came from. Used for display purposes only.

Since: 0.0.0.0

data CallStack

CallStacks are a lightweight method of obtaining a partial call-stack at any point in the program.

A function can request its call-site with the HasCallStack constraint. For example, we can define

putStrLnWithCallStack :: HasCallStack => String -> IO ()

as a variant of putStrLn that will get its call-site and print it, along with the string given as argument. We can access the call-stack inside putStrLnWithCallStack with callStack.

putStrLnWithCallStack :: HasCallStack => String -> IO ()
putStrLnWithCallStack msg = do
  putStrLn msg
  putStrLn (prettyCallStack callStack)

Thus, if we call putStrLnWithCallStack we will get a formatted call-stack alongside our string.

>>> putStrLnWithCallStack "hello"
hello
CallStack (from HasCallStack):
  putStrLnWithCallStack, called at <interactive>:2:1 in interactive:Ghci1

GHC solves HasCallStack constraints in three steps:

1. If there is a CallStack in scope -- i.e. the enclosing function has a HasCallStack constraint -- GHC will append the new call-site to the existing CallStack.
2. If there is no CallStack in scope -- e.g. in the GHCi session above -- and the enclosing definition does not have an explicit type signature, GHC will infer a HasCallStack constraint for the enclosing definition (subject to the monomorphism restriction).
3. If there is no CallStack in scope and the enclosing definition has an explicit type signature, GHC will solve the HasCallStack constraint for the singleton CallStack containing just the current call-site.

CallStacks do not interact with the RTS and do not require compilation with -prof. On the other hand, as they are built up explicitly via the HasCallStack constraints, they will generally not contain as much information as the simulated call-stacks maintained by the RTS.

A CallStack is a [(String, SrcLoc)]. The String is the name of function that was called, the SrcLoc is the call-site. The list is ordered with the most recently called function at the head.

NOTE: The intrepid user may notice that HasCallStack is just an alias for an implicit parameter ?callStack :: CallStack. This is an implementation detail and should not be considered part of the CallStack API, we may decide to change the implementation in the future.

Since: base-4.8.1.0

Instances

IsList CallStack

Be aware that 'fromList . toList = id' only for unfrozen CallStacks, since toList removes frozenness information.

Since: base-4.9.0.0

Defined in GHC.Exts

Associated Types

type Item CallStack :: Type

Methods

fromList :: [Item CallStack] -> CallStack

fromListN :: Int -> [Item CallStack] -> CallStack

toList :: CallStack -> [Item CallStack]

Show CallStack

Since: base-4.9.0.0

Defined in GHC.Show

Methods

showsPrec :: Int -> CallStack -> ShowS

show :: CallStack -> String

showList :: [CallStack] -> ShowS

NFData CallStack

Since: deepseq-1.4.2.0

Defined in Control.DeepSeq

Methods

rnf :: CallStack -> ()

type Item CallStack

Defined in GHC.Exts

type Item CallStack = (String, SrcLoc)

Convenience functions

displayCallStack :: CallStack -> Utf8Builder

Convert a CallStack value into a Utf8Builder indicating the first source location.

TODO Consider showing the entire call stack instead.

Since: 0.0.0.0

noLogging :: (HasLogFunc env, MonadReader env m) => m a -> m a

Disable logging capabilities in a given sub-routine

Intended to skip logging in general purpose implementations, where secrets might be logged accidently.

Since: 0.1.5.0

Accessors

logFuncUseColorL :: HasLogFunc env => SimpleGetter env Bool

Is the log func configured to use color output?

Intended for use by code which wants to optionally add additional color to its log messages.

Since: 0.1.0.0

Display

newtype Utf8Builder

A builder of binary data, with the invariant that the underlying data is supposed to be UTF-8 encoded.

Since: 0.1.0.0

Constructors

Utf8Builder

Fields

• getUtf8Builder :: Builder

Instances

IsString Utf8Builder

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

fromString :: String -> Utf8Builder

Semigroup Utf8Builder

Defined in RIO.Prelude.Display

Methods

(<>) :: Utf8Builder -> Utf8Builder -> Utf8Builder

sconcat :: NonEmpty Utf8Builder -> Utf8Builder

stimes :: Integral b => b -> Utf8Builder -> Utf8Builder

Monoid Utf8Builder

Defined in RIO.Prelude.Display

Methods

mempty :: Utf8Builder

mappend :: Utf8Builder -> Utf8Builder -> Utf8Builder

mconcat :: [Utf8Builder] -> Utf8Builder

Display Utf8Builder

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Utf8Builder -> Utf8Builder

textDisplay :: Utf8Builder -> Text

class Display a where

A typeclass for values which can be converted to a Utf8Builder. The intention of this typeclass is to provide a human-friendly display of the data.

Since: 0.1.0.0

Minimal complete definition

display | textDisplay

Methods

display :: a -> Utf8Builder

textDisplay :: a -> Text

Display data as Text, which will also be used for display if it is not overriden.

Since: 0.1.7.0

Instances

Display Char

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Char -> Utf8Builder

textDisplay :: Char -> Text

Display Double

Defined in RIO.Prelude.Display

Methods

display :: Double -> Utf8Builder

textDisplay :: Double -> Text

Display Float

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Float -> Utf8Builder

textDisplay :: Float -> Text

Display Int

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Int -> Utf8Builder

textDisplay :: Int -> Text

Display Int8

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Int8 -> Utf8Builder

textDisplay :: Int8 -> Text

Display Int16

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Int16 -> Utf8Builder

textDisplay :: Int16 -> Text

Display Int32

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Int32 -> Utf8Builder

textDisplay :: Int32 -> Text

Display Int64

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Int64 -> Utf8Builder

textDisplay :: Int64 -> Text

Display Integer

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Integer -> Utf8Builder

textDisplay :: Integer -> Text

Display Word

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Word -> Utf8Builder

textDisplay :: Word -> Text

Display Word8

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Word8 -> Utf8Builder

textDisplay :: Word8 -> Text

Display Word16

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Word16 -> Utf8Builder

textDisplay :: Word16 -> Text

Display Word32

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Word32 -> Utf8Builder

textDisplay :: Word32 -> Text

Display Word64

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Word64 -> Utf8Builder

textDisplay :: Word64 -> Text

Display IOException

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: IOException -> Utf8Builder

textDisplay :: IOException -> Text

Display SomeException

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: SomeException -> Utf8Builder

textDisplay :: SomeException -> Text

Display Text

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Text -> Utf8Builder

textDisplay :: Text -> Text0

Display Text

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Text -> Utf8Builder

textDisplay :: Text -> Text

Display Utf8Builder

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: Utf8Builder -> Utf8Builder

textDisplay :: Utf8Builder -> Text

Display (ProcessConfig a b c)

Since: 0.1.0.0

Defined in RIO.Prelude.Display

Methods

display :: ProcessConfig a b c -> Utf8Builder

textDisplay :: ProcessConfig a b c -> Text

displayShow :: Show a => a -> Utf8Builder

Use the Show instance for a value to convert it to a Utf8Builder.

Since: 0.1.0.0

utf8BuilderToText :: Utf8Builder -> Text

Convert a Utf8Builder value into a strict Text.

Since: 0.1.0.0

utf8BuilderToLazyText :: Utf8Builder -> Text

Convert a Utf8Builder value into a lazy Text.

Since: 0.1.0.0

displayBytesUtf8 :: ByteString -> Utf8Builder

Convert a ByteString into a Utf8Builder.

NOTE This function performs no checks to ensure that the data is, in fact, UTF8 encoded. If you provide non-UTF8 data, later functions may fail.

Since: 0.1.0.0

writeFileUtf8Builder :: MonadIO m => FilePath -> Utf8Builder -> m ()

Write the given Utf8Builder value to a file.

Since: 0.1.0.0

Lens

view :: MonadReader s m => Getting a s a -> m a

type ASetter s t a b = (a -> Identity b) -> s -> Identity t

ASetter s t a b is something that turns a function modifying a value into a function modifying a structure. If you ignore Identity (as Identity a is the same thing as a), the type is:

type ASetter s t a b = (a -> b) -> s -> t

The reason Identity is used here is for ASetter to be composable with other types, such as Lens.

Technically, if you're writing a library, you shouldn't use this type for setters you are exporting from your library; the right type to use is Setter, but it is not provided by this package (because then it'd have to depend on distributive). It's completely alright, however, to export functions which take an ASetter as an argument.

type ASetter' s a = ASetter s s a a

This is a type alias for monomorphic setters which don't change the type of the container (or of the value inside). It's useful more often than the same type in lens, because we can't provide real setters and so it does the job of both ASetter' and Setter'.

type Getting r s a = (a -> Const r a) -> s -> Const r s

Functions that operate on getters and folds – such as (^.), (^..), (^?) – use Getter r s a (with different values of r) to describe what kind of result they need. For instance, (^.) needs the getter to be able to return a single value, and so it accepts a getter of type Getting a s a. (^..) wants the getter to gather values together, so it uses Getting (Endo [a]) s a (it could've used Getting [a] s a instead, but it's faster with Endo). The choice of r depends on what you want to do with elements you're extracting from s.

type Lens s t a b = forall (f :: Type -> Type). Functor f => (a -> f b) -> s -> f t

Lens s t a b is the lowest common denominator of a setter and a getter, something that has the power of both; it has a Functor constraint, and since both Const and Identity are functors, it can be used whenever a getter or a setter is needed.

• a is the type of the value inside of structure
• b is the type of the replaced value
• s is the type of the whole structure
• t is the type of the structure after replacing a in it with b

type Lens' s a = Lens s s a a

This is a type alias for monomorphic lenses which don't change the type of the container (or of the value inside).

type SimpleGetter s a = forall r. Getting r s a

A SimpleGetter s a extracts a from s; so, it's the same thing as (s -> a), but you can use it in lens chains because its type looks like this:

type SimpleGetter s a =
  forall r. (a -> Const r a) -> s -> Const r s

Since Const r is a functor, SimpleGetter has the same shape as other lens types and can be composed with them. To get (s -> a) out of a SimpleGetter, choose r ~ a and feed Const :: a -> Const a a to the getter:

-- the actual signature is more permissive:
-- view :: Getting a s a -> s -> a
view :: SimpleGetter s a -> s -> a
view getter = getConst . getter Const

The actual Getter from lens is more general:

type Getter s a =
  forall f. (Contravariant f, Functor f) => (a -> f a) -> s -> f s

I'm not currently aware of any functions that take lens's Getter but won't accept SimpleGetter, but you should try to avoid exporting SimpleGetters anyway to minimise confusion. Alternatively, look at microlens-contra, which provides a fully lens-compatible Getter.

Lens users: you can convert a SimpleGetter to Getter by applying to . view to it.

lens :: (s -> a) -> (s -> b -> t) -> Lens s t a b

lens creates a Lens from a getter and a setter. The resulting lens isn't the most effective one (because of having to traverse the structure twice when modifying), but it shouldn't matter much.

A (partial) lens for list indexing:

ix :: Int -> Lens' [a] a
ix i = lens (!! i)                                   -- getter
            (\s b -> take i s ++ b : drop (i+1) s)   -- setter

Usage:

>>> [1..9] ^. ix 3
4

>>> [1..9] & ix 3 %~ negate
[1,2,3,-4,5,6,7,8,9]

When getting, the setter is completely unused; when setting, the getter is unused. Both are used only when the value is being modified. For instance, here we define a lens for the 1st element of a list, but instead of a legitimate getter we use undefined. Then we use the resulting lens for setting and it works, which proves that the getter wasn't used:

>>> [1,2,3] & lens undefined (\s b -> b : tail s) .~ 10
[10,2,3]

over :: ASetter s t a b -> (a -> b) -> s -> t

over is a synonym for (%~).

Getting fmap in a roundabout way:

over mapped :: Functor f => (a -> b) -> f a -> f b
over mapped = fmap

Applying a function to both components of a pair:

over both :: (a -> b) -> (a, a) -> (b, b)
over both = \f t -> (f (fst t), f (snd t))

Using over _2 as a replacement for second:

>>> over _2 show (10,20)
(10,"20")

set :: ASetter s t a b -> b -> s -> t

set is a synonym for (.~).

Setting the 1st component of a pair:

set _1 :: x -> (a, b) -> (x, b)
set _1 = \x t -> (x, snd t)

Using it to rewrite (<$):

set mapped :: Functor f => a -> f b -> f a
set mapped = (<$)

sets :: ((a -> b) -> s -> t) -> ASetter s t a b

sets creates an ASetter from an ordinary function. (The only thing it does is wrapping and unwrapping Identity.)

to :: (s -> a) -> SimpleGetter s a

to creates a getter from any function:

a ^. to f = f a

It's most useful in chains, because it lets you mix lenses and ordinary functions. Suppose you have a record which comes from some third-party library and doesn't have any lens accessors. You want to do something like this:

value ^. _1 . field . at 2

However, field isn't a getter, and you have to do this instead:

field (value ^. _1) ^. at 2

but now value is in the middle and it's hard to read the resulting code. A variant with to is prettier and more readable:

value ^. _1 . to field . at 2

(^.) :: s -> Getting a s a -> a infixl 8

(^.) applies a getter to a value; in other words, it gets a value out of a structure using a getter (which can be a lens, traversal, fold, etc.).

Getting 1st field of a tuple:

(^. _1) :: (a, b) -> a
(^. _1) = fst

When (^.) is used with a traversal, it combines all results using the Monoid instance for the resulting type. For instance, for lists it would be simple concatenation:

>>> ("str","ing") ^. each
"string"

The reason for this is that traversals use Applicative, and the Applicative instance for Const uses monoid concatenation to combine “effects” of Const.

A non-operator version of (^.) is called view, and it's a bit more general than (^.) (it works in MonadReader). If you need the general version, you can get it from microlens-mtl; otherwise there's view available in Lens.Micro.Extras.

Concurrency

data ThreadId

A ThreadId is an abstract type representing a handle to a thread. ThreadId is an instance of Eq, Ord and Show, where the Ord instance implements an arbitrary total ordering over ThreadIds. The Show instance lets you convert an arbitrary-valued ThreadId to string form; showing a ThreadId value is occasionally useful when debugging or diagnosing the behaviour of a concurrent program.

Note: in GHC, if you have a ThreadId, you essentially have a pointer to the thread itself. This means the thread itself can't be garbage collected until you drop the ThreadId. This misfeature will hopefully be corrected at a later date.

Instances

Eq ThreadId

Since: base-4.2.0.0

Defined in GHC.Conc.Sync

Methods

(==) :: ThreadId -> ThreadId -> Bool

(/=) :: ThreadId -> ThreadId -> Bool

Ord ThreadId

Since: base-4.2.0.0

Defined in GHC.Conc.Sync

Methods

compare :: ThreadId -> ThreadId -> Ordering

(<) :: ThreadId -> ThreadId -> Bool

(<=) :: ThreadId -> ThreadId -> Bool

(>) :: ThreadId -> ThreadId -> Bool

(>=) :: ThreadId -> ThreadId -> Bool

max :: ThreadId -> ThreadId -> ThreadId

min :: ThreadId -> ThreadId -> ThreadId

Show ThreadId

Since: base-4.2.0.0

Defined in GHC.Conc.Sync

Methods

showsPrec :: Int -> ThreadId -> ShowS

show :: ThreadId -> String

showList :: [ThreadId] -> ShowS

NFData ThreadId

Since: deepseq-1.4.0.0

Defined in Control.DeepSeq

Methods

rnf :: ThreadId -> ()

Hashable ThreadId

Defined in Data.Hashable.Class

Methods

hashWithSalt :: Int -> ThreadId -> Int

hash :: ThreadId -> Int

PrimUnlifted ThreadId

Since: primitive-0.6.4.0

Defined in Data.Primitive.UnliftedArray

Methods

toArrayArray# :: ThreadId -> ArrayArray#

fromArrayArray# :: ArrayArray# -> ThreadId

myThreadId :: MonadIO m => m ThreadId

Lifted version of myThreadId.

Since: unliftio-0.1.1.0

isCurrentThreadBound :: MonadIO m => m Bool

Lifted version of isCurrentThreadBound.

Since: unliftio-0.1.1.0

threadWaitRead :: MonadIO m => Fd -> m ()

Lifted version of threadWaitRead.

Since: unliftio-0.1.1.0

threadWaitWrite :: MonadIO m => Fd -> m ()

Lifted version of threadWaitWrite.

Since: unliftio-0.1.1.0

threadDelay :: MonadIO m => Int -> m ()

Lifted version of threadDelay.

Since: unliftio-0.1.1.0

yieldThread :: MonadIO m => m ()

Async

module UnliftIO.Async

STM

module UnliftIO.STM

Chan

module UnliftIO.Chan

Timeout

module UnliftIO.Timeout

Exceptions

module UnliftIO.Exception

Re-exported from Control.Monad.Catch:

throwM :: (MonadThrow m, Exception e) => e -> m a

Throw an exception. Note that this throws when this action is run in the monad m, not when it is applied. It is a generalization of Control.Exception's throwIO.

Should satisfy the law:

throwM e >> f = throwM e

Files and handles

module UnliftIO.IO

module UnliftIO.Temporary

withLazyFile :: MonadUnliftIO m => FilePath -> (ByteString -> m a) -> m a

Lazily get the contents of a file. Unlike readFile, this ensures that if an exception is thrown, the file handle is closed immediately.

readFileBinary :: MonadIO m => FilePath -> m ByteString

Same as readFile, but generalized to MonadIO

writeFileBinary :: MonadIO m => FilePath -> ByteString -> m ()

Same as writeFile, but generalized to MonadIO

readFileUtf8 :: MonadIO m => FilePath -> m Text

Read a file in UTF8 encoding, throwing an exception on invalid character encoding.

This function will use OS-specific line ending handling.

writeFileUtf8 :: MonadIO m => FilePath -> Text -> m ()

Write a file in UTF8 encoding

This function will use OS-specific line ending handling.

hPutBuilder :: MonadIO m => Handle -> Builder -> m ()

Exit

exitFailure :: MonadIO m => m a

Lifted version of "System.Exit.exitFailure".

@since 0.1.9.0.

exitSuccess :: MonadIO m => m a

Lifted version of "System.Exit.exitSuccess".

@since 0.1.9.0.

exitWith :: MonadIO m => ExitCode -> m a

Lifted version of "System.Exit.exitWith".

@since 0.1.9.0.

data ExitCode

Defines the exit codes that a program can return.

Constructors

ExitSuccess

indicates successful termination;

ExitFailure Int

indicates program failure with an exit code. The exact interpretation of the code is operating-system dependent. In particular, some values may be prohibited (e.g. 0 on a POSIX-compliant system).

Instances

Eq ExitCode

Defined in GHC.IO.Exception

Methods

(==) :: ExitCode -> ExitCode -> Bool

(/=) :: ExitCode -> ExitCode -> Bool

Ord ExitCode

Defined in GHC.IO.Exception

Methods

compare :: ExitCode -> ExitCode -> Ordering

(<) :: ExitCode -> ExitCode -> Bool

(<=) :: ExitCode -> ExitCode -> Bool

(>) :: ExitCode -> ExitCode -> Bool

(>=) :: ExitCode -> ExitCode -> Bool

max :: ExitCode -> ExitCode -> ExitCode

min :: ExitCode -> ExitCode -> ExitCode

Read ExitCode

Defined in GHC.IO.Exception

Methods

readsPrec :: Int -> ReadS ExitCode

readList :: ReadS [ExitCode]

readPrec :: ReadPrec ExitCode

readListPrec :: ReadPrec [ExitCode]

Show ExitCode

Defined in GHC.IO.Exception

Methods

showsPrec :: Int -> ExitCode -> ShowS

show :: ExitCode -> String

showList :: [ExitCode] -> ShowS

Generic ExitCode

Defined in GHC.IO.Exception

Associated Types

type Rep ExitCode :: Type -> Type

Methods

from :: ExitCode -> Rep ExitCode x

to :: Rep ExitCode x -> ExitCode

Exception ExitCode

Since: base-4.1.0.0

Defined in GHC.IO.Exception

Methods

toException :: ExitCode -> SomeException

fromException :: SomeException -> Maybe ExitCode

displayException :: ExitCode -> String

NFData ExitCode

Since: deepseq-1.4.2.0

Defined in Control.DeepSeq

Methods

rnf :: ExitCode -> ()

type Rep ExitCode

Defined in GHC.IO.Exception

type Rep ExitCode = D1 (MetaData "ExitCode" "GHC.IO.Exception" "base" False) (C1 (MetaCons "ExitSuccess" PrefixI False) (U1 :: Type -> Type) :+: C1 (MetaCons "ExitFailure" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 Int)))

Mutable Variables

SomeRef

class HasWriteRef w env | env -> w where

Environment values with writing capabilities to SomeRef

Since: 0.1.4.0

Methods

writeRefL :: Lens' env (SomeRef w)

Instances

HasWriteRef a (SomeRef a)

Identity write reference where the SomeRef is the env

Since: 0.1.4.0

Defined in RIO.Prelude.RIO

Methods

writeRefL :: Lens' (SomeRef a) (SomeRef a)

class HasStateRef s env | env -> s where

Environment values with stateful capabilities to SomeRef

Since: 0.1.4.0

Methods

stateRefL :: Lens' env (SomeRef s)

Instances

HasStateRef a (SomeRef a)

Identity state reference where the SomeRef is the env

Since: 0.1.4.0

Defined in RIO.Prelude.RIO

Methods

stateRefL :: Lens' (SomeRef a) (SomeRef a)

data SomeRef a

Abstraction over how to read from and write to a mutable reference

Since: 0.1.4.0

Instances

HasWriteRef a (SomeRef a)

Identity write reference where the SomeRef is the env

Since: 0.1.4.0

Defined in RIO.Prelude.RIO

Methods

writeRefL :: Lens' (SomeRef a) (SomeRef a)

HasStateRef a (SomeRef a)

Identity state reference where the SomeRef is the env

Since: 0.1.4.0

Defined in RIO.Prelude.RIO

Methods

stateRefL :: Lens' (SomeRef a) (SomeRef a)

readSomeRef :: MonadIO m => SomeRef a -> m a

Read from a SomeRef

Since: 0.1.4.0

writeSomeRef :: MonadIO m => SomeRef a -> a -> m ()

Write to a SomeRef

Since: 0.1.4.0

modifySomeRef :: MonadIO m => SomeRef a -> (a -> a) -> m ()

Modify a SomeRef This function is subject to change due to the lack of atomic operations

Since: 0.1.4.0

newSomeRef :: MonadIO m => a -> m (SomeRef a)

create a new boxed SomeRef

Since: 0.1.4.0

newUnboxedSomeRef :: (MonadIO m, Unbox a) => a -> m (SomeRef a)

create a new unboxed SomeRef

Since: 0.1.4.0

URef

data URef s a

An unboxed reference. This works like an IORef, but the data is stored in a bytearray instead of a heap object, avoiding significant allocation overhead in some cases. For a concrete example, see this Stack Overflow question: https://stackoverflow.com/questions/27261813/why-is-my-little-stref-int-require-allocating-gigabytes.

The first parameter is the state token type, the same as would be used for the ST monad. If you're using an IO-based monad, you can use the convenience IOURef type synonym instead.

Since: 0.0.2.0

type IOURef = URef (PrimState IO)

Helpful type synonym for using a URef from an IO-based stack.

Since: 0.0.2.0

newURef :: (PrimMonad m, Unbox a) => a -> m (URef (PrimState m) a)

Create a new URef

Since: 0.0.2.0

readURef :: (PrimMonad m, Unbox a) => URef (PrimState m) a -> m a

Read the value in a URef

Since: 0.0.2.0

writeURef :: (PrimMonad m, Unbox a) => URef (PrimState m) a -> a -> m ()

Write a value into a URef. Note that this action is strict, and will force evalution of the value.

Since: 0.0.2.0

modifyURef :: (PrimMonad m, Unbox a) => URef (PrimState m) a -> (a -> a) -> m ()

Modify a value in a URef. Note that this action is strict, and will force evaluation of the result value.

Since: 0.0.2.0

IORef

module UnliftIO.IORef

MVar

module UnliftIO.MVar

Memoize

module UnliftIO.Memoize

Deque

module RIO.Deque

Debugging

Trace

Text

trace :: Text -> a -> a

Warning: Trace statement left in code

Since: 0.1.0.0

traceId :: Text -> Text

Warning: Trace statement left in code

Since: 0.1.0.0

traceIO :: MonadIO m => Text -> m ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceM :: Applicative f => Text -> f ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceEvent :: Text -> a -> a

Warning: Trace statement left in code

Since: 0.1.0.0

traceEventIO :: MonadIO m => Text -> m ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceMarker :: Text -> a -> a

Warning: Trace statement left in code

Since: 0.1.0.0

traceMarkerIO :: MonadIO m => Text -> m ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceStack :: Text -> a -> a

Warning: Trace statement left in code

Since: 0.1.0.0

Show

traceShow :: Show a => a -> b -> b

Warning: Trace statement left in code

Since: 0.1.0.0

traceShowId :: Show a => a -> a

Warning: Trace statement left in code

Since: 0.1.0.0

traceShowIO :: (Show a, MonadIO m) => a -> m ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceShowM :: (Show a, Applicative f) => a -> f ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceShowEvent :: Show a => a -> b -> b

Warning: Trace statement left in code

Since: 0.1.0.0

traceShowEventIO :: (Show a, MonadIO m) => a -> m ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceShowMarker :: Show a => a -> b -> b

Warning: Trace statement left in code

Since: 0.1.0.0

traceShowMarkerIO :: (Show a, MonadIO m) => a -> m ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceShowStack :: Show a => a -> b -> b

Warning: Trace statement left in code

Since: 0.1.0.0

Display

traceDisplay :: Display a => a -> b -> b

Warning: Trace statement left in code

Since: 0.1.0.0

traceDisplayId :: Display a => a -> a

Warning: Trace statement left in code

Since: 0.1.0.0

traceDisplayIO :: (Display a, MonadIO m) => a -> m ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceDisplayM :: (Display a, Applicative f) => a -> f ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceDisplayEvent :: Display a => a -> b -> b

Warning: Trace statement left in code

Since: 0.1.0.0

traceDisplayEventIO :: (Display a, MonadIO m) => a -> m ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceDisplayMarker :: Display a => a -> b -> b

Warning: Trace statement left in code

Since: 0.1.0.0

traceDisplayMarkerIO :: (Display a, MonadIO m) => a -> m ()

Warning: Trace statement left in code

Since: 0.1.0.0

traceDisplayStack :: Display a => a -> b -> b

Warning: Trace statement left in code

Since: 0.1.0.0