4.15.4.4 Domain Errors

A domain error occurs when an input argument is of the right type but there is something wrong with its value. For example, the second argument to open/[3,4] is supposed to be an atom that represents a valid mode for opening a file, such as read or write. If a number or a compound term is given instead, then that is a type error. If an atom is given that is not a valid mode, then that is a domain error.

The main reason that we distinguish between type errors and domain errors is that they usually represent different sorts of mistakes in your program. A type error usually indicates that you have passed the wrong argument to a command, whereas a domain error usually indicates that you passed the argument you meant to check, but you hadn’t checked it enough.

The SICStus_Error term associated with a domain error is

domain_error(Goal, ArgNo, DomainName, Culprit)

The arguments correspond to those of the SICStus_Error term for a type error, except that DomainName is not in general the name of a unary predicate: it needn’t even be an atom. For example, if some command requires an argument to be an integer in the range 1..99, then it might use between(1,99) as the DomainName. With respect to the date_plus example under Type Errors, if the month had been given as 13, then it would have passed the type test but would throw a domain error.

For example, the goal

open(somefile,rread,S)

throws the exception

error(domain_error(io_mode,rread),
      domain_error(open(somefile,rread,_A),2,io_mode,rread))

The Message argument is used to provide extra information about the problem.