System.Environment.FromEnv

Core class

class FromEnv a where

Class for things that can be created from environment variables.

Minimal complete definition

Nothing

Methods

fromEnv :: MonadIO m => m (Either FromEnvError a)

default fromEnv :: (MonadIO m, Generic a, GFromEnv' (Rep a)) => m (Either FromEnvError a)

Instances

(FromEnv a, FromEnv b) => FromEnv (a, b)

Defined in System.Environment.FromEnv

Methods

fromEnv :: MonadIO m => m (Either FromEnvError (a, b))

(FromEnv a, FromEnv b, FromEnv c) => FromEnv (a, b, c)

Defined in System.Environment.FromEnv

Methods

fromEnv :: MonadIO m => m (Either FromEnvError (a, b, c))

Options

defaultEnvOpts :: FromEnvOptions

Default FromEnvOptions:

The default options will try to read a field name fieldName from an environment variables FIELD_NAME, as this is the most common naming convention for environment variables.

If you want different behavior, see gFromEnv.

FromEnvOptions
{ optsFieldLabelModifier = Just . screamingSnake
}

data FromEnvOptions

Options to specify how to construct your datatype from environment variables. Options can be set using record update syntax and defaultEnvOpts.

Generic parsing class

class GFromEnv a where

Minimal complete definition

Nothing

Methods

gFromEnv :: MonadIO m => FromEnvOptions -> m (Either FromEnvError a)

Try to construct a value from environment variables.

default gFromEnv :: (MonadIO m, Generic a, GFromEnv' (Rep a)) => FromEnvOptions -> m (Either FromEnvError a)

Instances

(Generic a, GFromEnv' (Rep a)) => GFromEnv a

Defined in System.Environment.FromEnv

Methods

gFromEnv :: MonadIO m => FromEnvOptions -> m (Either FromEnvError a)

Errors

data FromEnvError

Constructors

UnsetVariable String

A field was unset in the environment

FailedToParse String String

Failed to parse a given field from an environment variable

AggregateError [FromEnvError]

There was more than one error.

Instances

Show FromEnvError

Defined in System.Environment.FromEnv

Methods

showsPrec :: Int -> FromEnvError -> ShowS

show :: FromEnvError -> String

showList :: [FromEnvError] -> ShowS

Eq FromEnvError

Defined in System.Environment.FromEnv

Methods

(==) :: FromEnvError -> FromEnvError -> Bool

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