package org.simantics.scl.compiler.types.kinds;

import org.simantics.scl.compiler.types.util.TypeUnparsingContext;

/**
 * This is an abstract base class for type kinds. It has three child classes:
 * KCon for constants, KArrow for kind arrows and KMetaVar for kind meta-variables.
 * 
 * Child classes need to implement the method {@link #contains(KMetaVar)}, which
 * returns true, if a given kind meta-variable points to this instance.
 * 
 * The default implementation of {@link #toString()} is infinitely recursive, with
 * {@link #toString(TypeUnparsingContext, StringBuilder)} and {@link #toStringPar(TypeUnparsingContext, StringBuilder)}
 * both calling each other. 
 */
public abstract class Kind {
    public static final Kind[] EMPTY_ARRAY = new Kind[0];
    
    @Override
    public String toString() {
        return toString(new TypeUnparsingContext());
    }

    public String toString(TypeUnparsingContext tuc) {
        StringBuilder b = new StringBuilder();
        toString(tuc, b);
        return b.toString();
    }

    /**
     * Write this kind to a string builder as an unparenthesized expression.
     * If a subclass does not need parenthesis, it can implement the
     * {@link #toStringPar(TypeUnparsingContext, StringBuilder)} method instead.
     */
    protected void toString(TypeUnparsingContext tuc, StringBuilder b) {
        toStringPar(tuc, b);
    }
    
    /**
     * Write this kind to a string builder as an atomic expression. The default implementation
     * encloses the output of {@link #toString(TypeUnparsingContext, StringBuilder)} in parenthesis.
     */
    protected void toStringPar(TypeUnparsingContext tuc, StringBuilder b) {
        b.append("(");
        toString(tuc, b);
        b.append(")");
    }

    /**
     * Return true, if this kind has been unified with the given kind meta-variable.
     */
    public abstract boolean contains(KMetaVar var);
}