lib.types.either

The following is the current implementation of this function.

either = t1: t2: mkOptionType rec {
      name = "either";
      description =
        if t1.descriptionClass or null == "nonRestrictiveClause"
        then
          # Plain, but add comma
          "${t1.description}, or ${optionDescriptionPhrase (class: class == "noun" || class == "conjunction") t2}"
        else
          "${optionDescriptionPhrase (class: class == "noun" || class == "conjunction") t1} or ${optionDescriptionPhrase (class: class == "noun" || class == "conjunction" || class == "composite") t2}";
      descriptionClass = "conjunction";
      check = x: t1.check x || t2.check x;
      merge = loc: defs:
        let
          defList = map (d: d.value) defs;
        in
          if   all (x: t1.check x) defList
               then t1.merge loc defs
          else if all (x: t2.check x) defList
               then t2.merge loc defs
          else mergeOneOption loc defs;
      typeMerge = f':
        let mt1 = t1.typeMerge (elemAt f'.wrapped 0).functor;
            mt2 = t2.typeMerge (elemAt f'.wrapped 1).functor;
        in
           if (name == f'.name) && (mt1 != null) && (mt2 != null)
           then functor.type mt1 mt2
           else null;
      functor = (defaultFunctor name) // { wrapped = [ t1 t2 ]; };
      nestedTypes.left = t1;
      nestedTypes.right = t2;
    };