package net.fortytwo.ripple.libs.math;
import net.fortytwo.flow.Sink;
import net.fortytwo.ripple.RippleException;
import net.fortytwo.ripple.model.ModelConnection;
import net.fortytwo.ripple.model.NumericValue;
import net.fortytwo.ripple.model.PrimitiveStackMapping;
import net.fortytwo.ripple.model.RippleList;
import net.fortytwo.ripple.model.StackMapping;
/**
* A primitive which consumes a number and produces its absolute value.
*
* @author Joshua Shinavier (http://fortytwo.net)
*/
public class Abs extends PrimitiveStackMapping {
private static final int ARITY = 1;
private final StackMapping self = this;
private static final String[] IDENTIFIERS = {
MathLibrary.NS_2013_03 + "abs",
MathLibrary.NS_2008_08 + "abs",
MathLibrary.NS_2007_08 + "abs",
MathLibrary.NS_2007_05 + "abs"};
public String[] getIdentifiers() {
return IDENTIFIERS;
}
public Abs()
throws RippleException {
super();
}
public Parameter[] getParameters() {
return new Parameter[]{
new Parameter("x", null, true)};
}
public String getComment() {
return "x => absolute value of x";
}
public void apply(final RippleList arg,
final Sink<RippleList> solutions,
final ModelConnection mc) throws RippleException {
RippleList stack = arg;
NumericValue a, result;
a = mc.toNumericValue(stack.getFirst());
stack = stack.getRest();
result = a.abs();
solutions.put(
stack.push(result));
}
@Override
public StackMapping getInverse() throws RippleException {
return absInverse;
}
private StackMapping absInverse = new StackMapping() {
public int arity() {
return ARITY;
}
public StackMapping getInverse() throws RippleException {
return self;
}
public boolean isTransparent() {
return true;
}
public void apply(final RippleList arg,
final Sink<RippleList> solutions,
final ModelConnection mc) throws RippleException {
RippleList stack = arg;
NumericValue a;
a = mc.toNumericValue(stack.getFirst());
stack = stack.getRest();
// Negative values are not the absolute value of any number.
if (a.doubleValue() >= 0) {
// Push the number itself.
solutions.put(
stack.push(a));
// If the number is nonzero, also push its negation.
if (a.doubleValue() > 0) {
solutions.put(
stack.push(a.neg()));
}
}
}
};
}