ASTTId.java

import java.util.HashSet;
import java.util.Set;

public class ASTTId implements ASTType	{	

    String id;	
    
    public ASTTId(String id)	{
        this.id = id;
    }

    @Override
    public String toStr() {
        return id;
    }

    @Override
    public boolean eqt(ASTType t)
    {
        return (id.equals(t.toStr()));
    }

    @Override
    public boolean subtypeOf(ASTType t, Environment<ASTType> e, Set<String> seen)
            throws InterpreterError {

        if (t instanceof ASTTId other && this.id.equals(other.id))
            return true;

        Set<String> nextSeen = new HashSet<>(seen);
        String pair = this.toStr() + "<:" + t.toStr();

        if (nextSeen.contains(pair)) return true;
        nextSeen.add(pair);

        ASTType resolvedThis = ASTTypeDef.unfold(this, e);
        ASTType resolvedTarget = ASTTypeDef.unfold(t, e);

        if (resolvedThis instanceof ASTTId || resolvedTarget instanceof ASTTId) {
            return resolvedThis.toStr().equals(resolvedTarget.toStr());
        }

        return resolvedThis.subtypeOf(resolvedTarget, e, nextSeen);
    }

}