io.parsingdata.metal.expression.value

Class Fold

java.lang.Object

io.parsingdata.metal.expression.value.Fold

All Implemented Interfaces:

ValueExpression

Direct Known Subclasses:

FoldLeft, FoldRight

public abstract class Fold
extends Object
implements ValueExpression

Base class for ValueExpression implementations of the Fold operation.

Fold has three operands: values (a ValueExpression), reducer (a Reducer) and initial (a ValueExpression). First initial is evaluated. If it does not return a single value, the final result is an empty list. Next, values is evaluated and its result is passed to the abstract prepareValues(ImmutableList) method. The returned list is prefixed by the value returned by evaluating initial. On this list, the reducer is applied to the first two values until a single value remains, which is then returned.

Field Summary

Fields

Modifier and Type	Field and Description
ValueExpression	initial
Reducer	reducer
ValueExpression	values

Constructor Summary

Constructors

Constructor and Description
Fold(ValueExpression values, Reducer reducer, ValueExpression initial)

Method Summary

Modifier and Type	Method and Description
ImmutableList<OptionalValue>	eval(Environment environment, Encoding encoding)
protected abstract ImmutableList<OptionalValue>	prepareValues(ImmutableList<OptionalValue> values)
protected abstract ValueExpression	reduce(Reducer reducer, Value head, Value tail)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

values

public final ValueExpression values

reducer

public final Reducer reducer

initial

public final ValueExpression initial

Constructor Detail

Fold

public Fold(ValueExpression values,
            Reducer reducer,
            ValueExpression initial)

Method Detail

eval

public ImmutableList<OptionalValue> eval(Environment environment,
                                         Encoding encoding)

Specified by:

eval in interface ValueExpression

prepareValues

protected abstract ImmutableList<OptionalValue> prepareValues(ImmutableList<OptionalValue> values)

reduce

protected abstract ValueExpression reduce(Reducer reducer,
                                          Value head,
                                          Value tail)