Err package:lens

Make a Monoid out of Either for error handling.

errno leading to this error, if any.

What type of error it is

This is thrown when the user calls error.

A class method without a definition (neither a default definition, nor a definition in the appropriate instance) was called.

An uninitialised record field was used.

A record selector was applied to a constructor without the appropriate field. This can only happen with a datatype with multiple constructors, where some fields are in one constructor but not another.

A record update was performed on a constructor without the appropriate field. This can only happen with a datatype with multiple constructors, where some fields are in one constructor but not another.

An expression that didn't typecheck during compile time was called. This is only possible with -fdefer-type-errors.

Retrieve the argument given to error. ErrorCall is isomorphic to a String.

>>> catching _ErrorCall (error "touch down!") return
"touch down!"

_ErrorCall :: Prism' ErrorCall     String
_ErrorCall :: Prism' SomeException String

Extract a description of the missing method.

_NoMethodError :: Prism' NoMethodError String
_NoMethodError :: Prism' SomeException String