Err

The GHC.Err module defines the code for the wired-in error functions, which have a special type in the compiler (with "open tyvars"). We cannot define these functions in a module where they might be used (e.g., GHC.Base), because the magical wired-in type will get confused with what the typechecker figures out.

Make a Monoid out of Either for error handling.

A command-line error message

This is used to report an error. What went wrong, some supplemental docs and a set of things expected at the current location. This does not, however, include the actual location.

ZMQ_POLLERR

The GHC.Err module defines the code for the wired-in error functions, which have a special type in the compiler (with "open tyvars"). We cannot define these functions in a module where they might be used (e.g., GHC.Base), because the magical wired-in type will get confused with what the typechecker figures out.

Unrecoverble-by-default error.

Error value hole