import ceylon.ast.core {

"""A utility function to create a [[BaseType]] directly from a string,
   without having to use [[TypeNameWithTypeArguments]] (a rather verbose name).
   This function is not suitable in all cases; if the following restrictions affect you,
   you should instead use the regular constructors:
   - the type arguments will all be invariant, use-site variance is unavailable
   - empty [[typeArguments]] mean the absence of a type argument list;
     an empty but present [[type argument list|TypeArguments]] is unavailable
   Usage examples:
       baseType("String") // String
       baseType("Sequence", "Integer") // Sequence<Integer>"""
shared BaseType baseType(IdentifierIsh name, IdentifierIsh|Type* typeArguments) {
    Type toType(IdentifierIsh|Type typeArgument) {
        switch (typeArgument)
        case (is IdentifierIsh) { return baseType(typeArgument); }
        case (is Type) { return typeArgument; }
    TypeArguments? args;
    if (typeArguments nonempty) { // non-narrowing check because the narrowing would be useless; collect() loses nonemptiness info, so we have to assert below anyways
        assert (nonempty ta =;
        args = TypeArguments(ta);
    } else {
        args = null;
    return BaseType(TypeNameWithTypeArguments(uidentifier(name), args));