Try is a synonym for Either ShowS. Used for results of partial functions which return either Right something when defined or Left r when there is a problem where r is a (prepending) failure report. Note: ShowS = String -> String makes prepending Strings efficient as composition Note: Either ShowS (and hence Try) is a monad, and this is used frequently for combining partial operations.

onFail s exp - prepends s at the front of a failure report if exp fails with Left report but does nothing otherwise.

nothingFail a s - Converts a Maybe Result (a) into a Try result by treating Nothing as a failure (the String s is used for the failure report on failure). Usually used as infix (exp nothingFail s)

failReport s - creates a failure (Left), prepending s for the failure report

failReports ss - creates a failure (Left), concatenating ss for the failure report

Extract the (Right) result from a Try, raising an error if the Try is Left r. The failure report (from Left r) is converted to a Stirng and passed to error.

ifFail a tr - extracts the (Right) result from tr but returning a if tr is Left _ .

a try result is a failure if it is a Left

Combines a list of Trys into a single Try with failure overriding success. It concatenates all failure reports if there are any and returns a single Left r. Otherwise it produces Right rs where rs is the list of all (successful) results. In particular, concatFails [] = Right [] (so is NOT a fail)

Combines a list of Trys into a list of the successes, ignoring any failures. In particular, ignoreFails [] = []

tryAtLeastOne rs - returns Right with the list of successful results if there are any, but Left with a fail report otherwise. The error report will include the concatenated reports from multiple failures.

atLeastOne rs - returns the list of successful results if there are any, but fails with an error otherwise. The error report will include the concatenated reports from multiple failures.