2 ms·

Non-termination makes perfect sense, but would you mind sharing a layman explanation of what you mean by the effects of partiality?

• nandemo 13y ago
  Roughly speaking, partial functions are functions that might crash -- or that might throw exceptions, if you prefer. So even if it always terminates, it might to do so at the cost of not returning a value of the expected type. A bit more precisely, a partial function is a function that is not defined for some values of its domain (its input). A well-known instance is the division operator, which is not defined when the divisor is zero. Other common examples are head and last: -- this promises to receive a list of elements of some type t and return the first element head :: [t] -> t head (first:rest) = first head [] = error "that list has no head, yo!" Where error is analogous to throwing an unchecked Throwable (eg RuntimeException) in Java. One solution is to use a safer version that returns Maybe a instead of a. This is analogous to using checked exceptions. safeHead :: [a] -> Maybe a safeHead (first:rest) = Just first safeHead [] = Nothing The solution above is common and idiomatic. Another option is to accept only arguments of a different list type that's guaranteed to be non-empty.