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 BinaryOperator) 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
BinaryOperator<ValueExpression>	reducer
ValueExpression	values

Constructor Summary

Constructors

Constructor and Description
Fold(ValueExpression values, BinaryOperator<ValueExpression> reducer, ValueExpression initial)

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object obj)
ImmutableList<Optional<Value>>	eval(ParseState parseState, Encoding encoding)
int	hashCode()
protected abstract ImmutableList<Optional<Value>>	prepareValues(ImmutableList<Optional<Value>> values)
protected abstract ValueExpression	reduce(BinaryOperator<ValueExpression> reducer, Value head, Value tail)
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

values

public final ValueExpression values

reducer

public final BinaryOperator<ValueExpression> reducer

initial

public final ValueExpression initial

Constructor Detail

Fold

public Fold(ValueExpression values,
            BinaryOperator<ValueExpression> reducer,
            ValueExpression initial)

Method Detail

eval

public ImmutableList<Optional<Value>> eval(ParseState parseState,
                                           Encoding encoding)

Specified by:

eval in interface ValueExpression

prepareValues

protected abstract ImmutableList<Optional<Value>> prepareValues(ImmutableList<Optional<Value>> values)

reduce

protected abstract ValueExpression reduce(BinaryOperator<ValueExpression> reducer,
                                          Value head,
                                          Value tail)

toString

public String toString()

Overrides:

toString in class Object

equals

public boolean equals(Object obj)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object