Module

Control.Monad.Except.Checked

Package: purescript-checked-exceptions
Repository: natefaubion/purescript-checked-exceptions

Extensible checked exceptions with polymorphic variants

This module provides helpers for using Variant with ExceptT. When combined, we get a mechanism for extensible, checked exceptions. That is, exceptions can be defined and used anywhere, and handled as needed. Handling an exception eliminates it from the type, giving us proof that it no longer occurs.

#ExceptV Source

type ExceptV exc = ExceptT (Variant exc)

#handleError Source

handleError :: forall a rl excOut excIn excHandled handlers m. RowToList handlers rl => VariantMatchCases rl excHandled (ExceptV excOut m a) => Union excHandled excOut excIn => Monad m => Record handlers -> ExceptV excIn m a -> ExceptV excOut m a

Catches and eliminates exceptions given a record of handlers. Unhandled exceptions are re-propragated. Record fields map to the label for the exception being handled.

An example for handling HTTP exceptions might be:

request # handleError
  { httpNotFound: \_ -> ...
  , httpServerError: \error -> ...
  }

#safe Source

safe :: forall a m. Functor m => ExceptV () m a -> m a

Safely removes the ExceptT layer when all exceptions have been handled.

Modules: Control.Monad.Except.Checked