Effect.Ref
- Package
- purescript-refs
- Repository
- purescript/purescript-refs
This module defines the Ref type for mutable value references, as well
as actions for working with them.
You'll notice that all of the functions that operate on a Ref (e.g.
new, read, write) return their result wrapped in an Effect.
Working with mutable references is considered effectful in PureScript
because of the principle of purity: functions should not have side
effects, and should return the same result when called with the same
arguments. If a Ref could be written to without using Effect, that
would cause a side effect (the effect of changing the result of subsequent
reads for that Ref). If there were a function for reading the current
value of a Ref without the result being wrapped in Effect, the result
of calling that function would change each time a new value was written to
the Ref. Even creating a new Ref is effectful: if there were a
function for creating a new Ref with the type forall s. s -> Ref s,
then calling that function twice with the same argument would not give the
same result in each case, since you'd end up with two distinct references
which could be updated independently of each other.
Note: Control.Monad.ST provides a pure alternative to Ref when
mutation is restricted to a local scope.
#newWithSelf Source
newWithSelf :: forall s. (Ref s -> s) -> Effect (Ref s)Create a new mutable reference containing a value that can refer to the
Ref being created.
- Modules
- Effect.
Ref