4.15.4.2 Uninstantiation Errors

An uninstantiation error occurs when a predicate or command is called with one of its input arguments instantiated when an unbound variable was expected.

The SICStus_Error term associated with an instantiation error is

uninstantiation_error(Goal,ArgNo,Culprit)

For example, the goal

open(f, write, bar)

throws the exception

error(uninstantiation_error(bar),
      uninstantiation_error(open(f,write,bar),3,bar))

because the third argument was not a variable.