Henning Thielemann wrote:

What is the reason for the definition

ReadS a = [(a, String)]

not being

ReadS a = Maybe (a, String)

? The latter one reflects that either one or no value is read, whereas the first definition allows an arbitrary number of read values which is confusing and unsafe in my opinion.

List is a backtracking monad, while Maybe is merely an error monad. You have to have backtracking to bet better than LL(1) or LR(1) parsing, and LL(1) is not an acceptable restriction for a fundamental function like read. Jonathan Cast