// atom_codes/2 see ISO §8.16.5
func BuiltinAtomCodes2(m Machine, args []term.Term) ForeignReturn {
if !term.IsVariable(args[0]) {
atom := args[0].(*term.Atom)
list := term.NewCodeList(atom.Name())
return ForeignUnify(args[1], list)
} else if !term.IsVariable(args[1]) {
runes := make([]rune, 0)
list := args[1].(term.Callable)
for {
switch list.Arity() {
case 2:
if list.Name() == "." {
args := list.Arguments()
code := args[0].(*term.Integer)
runes = append(runes, code.Code())
list = args[1].(term.Callable)
}
case 0:
if list.Name() == "[]" {
atom := term.NewAtom(string(runes))
return ForeignUnify(args[0], atom)
}
default:
msg := fmt.Sprintf("unexpected code list %s", args[1])
panic(msg)
}
}
}
msg := fmt.Sprintf("atom_codes/2: error with the arguments %s and %s", args[0], args[1])
panic(msg)
}
// var(?X) is semidet.
//
// True if X is a variable.
func BuiltinVar1(m Machine, args []term.Term) ForeignReturn {
x := args[0]
if term.IsVariable(x) {
return ForeignTrue()
}
return ForeignFail()
}
// downcase_atom(+AnyCase, -LowerCase)
//
// Converts the characters of AnyCase into lowercase and unifies the
// lowercase atom with LowerCase.
func BuiltinDowncaseAtom2(m Machine, args []term.Term) ForeignReturn {
if term.IsVariable(args[0]) {
panic("downcase_atom/2: instantiation_error")
}
anycase := args[0].(term.Callable)
if anycase.Arity() != 0 {
msg := fmt.Sprintf("downcase_atom/2: type_error(atom, %s)", anycase)
panic(msg)
}
lowercase := term.NewAtom(strings.ToLower(anycase.Name()))
return ForeignUnify(args[1], lowercase)
}
// atom_number/2 as defined in SWI-Prolog
func BuiltinAtomNumber2(m Machine, args []term.Term) (ret ForeignReturn) {
number := args[1]
if !term.IsVariable(args[0]) {
atom := args[0].(term.Callable)
defer func() { // convert parsing panics into fail
if x := recover(); x != nil {
ret = ForeignFail()
}
}()
if strings.Contains(atom.Name(), ".") {
number = term.NewFloat(atom.Name())
} else {
number = term.NewInt(atom.Name())
}
return ForeignUnify(args[1], number)
} else if !term.IsVariable(number) {
atom := term.NewAtom(number.String())
return ForeignUnify(args[0], atom)
}
msg := fmt.Sprintf("atom_number/2: Arguments are not sufficiently instantiated: %s and %s", args[0], args[1])
panic(msg)
}