bug117.m:028: In clause for `extract(in) = out(list.non_empty_list)':
bug117.m:028:   mode error: the function result did not get sufficiently
bug117.m:028:   instantiated.
bug117.m:028:   Final instantiatedness of `X' was `ground',
bug117.m:028:   expected final instantiatedness was
bug117.m:028:     named inst list.non_empty_list
bug117.m:028:     which expands to
bug117.m:028:       bound(
bug117.m:028:         '[|]'(ground, ground)
bug117.m:028:       ).