mod -package:base

Not on Stackage, so not searched. Fast type-safe modular arithmetic

pattern synonym for remainder %

pattern synonym for remainder %

A different MonadError analogue to the withExceptT function. Modify the value (and possibly the type) of an error in an ExceptT-transformed monad, while stripping the ExceptT layer. This is useful for adapting the MonadError constraint of a computation. For example:

data DatabaseError = ...

performDatabaseQuery :: (MonadError DatabaseError m, ...) => m PersistedValue

data AppError
= MkDatabaseError DatabaseError
| ...

app :: (MonadError AppError m, ...) => m ()

Given these types, performDatabaseQuery cannot be used directly inside app, because the error types don't match. Using modifyError, an equivalent function with a different error type can be constructed:

performDatabaseQuery' :: (MonadError AppError m, ...) => m PersistedValue
performDatabaseQuery' = modifyError MkDatabaseError performDatabaseQuery

Since the error types do match, performDatabaseQuery' _can_ be used in app, assuming all other constraints carry over. This works by instantiating the m in the type of performDatabaseQuery to ExceptT DatabaseError m', which satisfies the MonadError DatabaseError constraint. Immediately, the ExceptT DatabaseError layer is unwrapped, producing Either a DatabaseError or a PersistedValue. If it's the former, the error is wrapped in MkDatabaseError and re-thrown in the inner monad, otherwise the result value is returned.

Monadic state transformer. Maps an old state to a new state inside a state monad. The old state is thrown away.

Main> :t modify ((+1) :: Int -> Int)
modify (...) :: (MonadState Int a) => a ()

This says that modify (+1) acts over any Monad that is a member of the MonadState class, with an Int state.

A variant of modify in which the computation is strict in the new state.

modify f is an action that updates the state to the result of applying f to the current state.

• modify f = get >>= (put .
  f)

modify f is an action that updates the state to the result of applying f to the current state.

• modify f = get >>= (put .
  f)

modify f is an action that updates the state to the result of applying f to the current state.

• modify f = get >>= (put .
  f)

A variant of modify in which the computation is strict in the new state.

• modify' f = get >>= (($!)
  put . f)

A variant of modify in which the new state is generated by a monadic action.

A variant of modify in which the computation is strict in the new state.

• modify' f = get >>= (($!)
  put . f)

Note that this is only strict in the top level of the state. Lazy components of the state will not be evaluated unless f evaluates them.

Apply a destructive operation to a vector. The operation may be performed in place if it is safe to do so and will modify a copy of the vector otherwise (see New for details).

Examples

>>> import qualified Data.Vector as V

>>> import qualified Data.Vector.Mutable as MV

>>> V.modify (\v -> MV.write v 0 'x') $ V.replicate 4 'a'
"xaaa"

Apply a destructive operation to a vector. The operation may be performed in place if it is safe to do so and will modify a copy of the vector otherwise (see New for details).

Examples

>>> import qualified Data.Vector.Strict as V

>>> import qualified Data.Vector.Strict.Mutable as MV

>>> V.modify (\v -> MV.write v 0 'x') $ V.replicate 4 'a'
"xaaa"

Modify the element at the given position.

Modify the element at the given position using a monadic function.

Modify the element at the given position.

Modify the element at the given position using a monadic function.

Apply a destructive operation to a vector. The operation may be performed in place if it is safe to do so and will modify a copy of the vector otherwise (see New for details).

Examples

>>> import qualified Data.Vector.Primitive as VP

>>> import qualified Data.Vector.Primitive.Mutable as MVP

>>> VP.modify (\v -> MVP.write v 0 'x') $ VP.replicate 4 'a'
"xaaa"

Modify the element at the given position.