Copyright | (c) 2019 Kowainik |
---|---|

License | MPL-2.0 |

Maintainer | Kowainik <xrom.xkov@gmail.com> |

Safe Haskell | None |

Language | Haskell2010 |

This module contains logging effect which can be interpreted in terms of
`LogAction`

from the `co-log-core`

package.

## Synopsis

- data Log (msg :: Type) (m :: Type -> Type) (a :: Type) where
- log :: forall msg r. Member (Log msg) r => msg -> Sem r ()
- runLogAction :: forall m msg r a. Member (Lift m) r => LogAction m msg -> Sem (Log msg ': r) a -> Sem r a
- runLogAsTrace :: forall r a. Member Trace r => Sem (Log String ': r) a -> Sem r a
- runLogAsOutput :: forall msg r a. Member (Output msg) r => Sem (Log msg ': r) a -> Sem r a
- runTraceAsLog :: forall r a. Member (Log String) r => Sem (Trace ': r) a -> Sem r a
- runOutputAsLog :: forall msg r a. Member (Log msg) r => Sem (Output msg ': r) a -> Sem r a

# Effect

data Log (msg :: Type) (m :: Type -> Type) (a :: Type) where Source #

Effect responsible for logging messages of type `msg`

. Has similar
structure to `LogAction`

.

You can think of this effect in the following way in terms of the existing
effects in `polysemy`

:

# Actions

# Interpretations

runLogAction :: forall m msg r a. Member (Lift m) r => LogAction m msg -> Sem (Log msg ': r) a -> Sem r a Source #

Run a `Log`

effect in terms of the given `LogAction`

. The idea behind this
function is the following: if you have

then you can use this
action to tell how to io interpret effect `LogAction`

m msg`Log`

. However, this is only possible
if you also have

effect because running log action requires access to
monad `Lift`

m`m`

.

This function allows to use extensible effects provided by the `polysemy`

library with logging provided by `co-log`

. You can construct `LogAction`

independently and then just pass to this function to tell how to log messages.

Several examples:

: interprets the`runLogAction`

mempty`Log`

effect by ignoring all messages.

: interprets`runLogAction`

`logStringStdout`

`Log`

effect by allowing to log`String`

to`stdout`

.