Method join

chapter21/src/main/java/com/seaofnodes/simple/type/Type.java:187–190

(Type t)

    // Our lattice is defined with a MEET and a DUAL.
    // JOIN is dual of meet of both duals.
    public final Type join(Type t) {
        if( this==t ) return this;
        return dual().meet(t.dual()).dual();
    }

    // True if this "isa" t; e.g. 17 isa TypeInteger.BOT
    public boolean isa( Type t ) { return meet(t)==t; }