Package org.organicdesign.fp.xform
Class Xform<A>
- java.lang.Object
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- org.organicdesign.fp.xform.Xform<A>
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- All Implemented Interfaces:
java.lang.Iterable<A>
,UnmodIterable<A>
,Transformable<A>
public abstract class Xform<A> extends java.lang.Object implements UnmodIterable<A>
An immutable description of operations to be performed (a transformation, transform, or x-form). When fold() (or another terminating function) is called, the Xform definition is "compiled" into a one-time mutable transformation which is then carried out. This allows certain performance shortcuts (such as doing a drop with index addition instead of iteration) and also hides the mutability otherwise inherent in a transformation. Xform is an abstract class. Most of the methods on Xform produce immutable descriptions of actions to take at a later time. These are represented by ___Desc classes. When fold() is called (or any of the helper methods that wrap it), that produces a result by first stringing together a bunch of Operations (____Op classes) and then "running" them. This is analogous to compiling a program and running it. The ____Desc classes are like the immutable source, the ____Op classes like the op-codes it's compiled into. Special thanks to Nathan Williams for pointing me toward separating the mutation from the description of a transformation. Also to Paul Phillips (@extempore2) whose lectures provided an outline for what was ideal and also what was important. All errors are my own. -Glen 2015-08-30
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Nested Class Summary
Nested Classes Modifier and Type Class Description protected static class
Xform.RunList
A RunList is a list of Operations "compiled" from an Xform.
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Method Summary
All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description Xform<A>
concat(java.lang.Iterable<? extends A> list)
Add items to the end of this Transformable (precat() adds to the beginning)Xform<A>
drop(long n)
The number of items to drop from the beginning of the output.Xform<A>
dropWhile(Fn1<? super A,java.lang.Boolean> predicate)
The number of items to drop from the beginning of the output.static <T> Xform<T>
empty()
Xform<A>
filter(Fn1<? super A,java.lang.Boolean> f)
Return only the items for which the given predicate returns true.<B> Xform<B>
flatMap(Fn1<? super A,java.lang.Iterable<B>> f)
Transform each item into zero or more new items using the given function.<B> B
fold(B ident, Fn2<? super B,? super A,B> reducer)
Provides a way to collect the results of the transformation.<G,B>
Or<G,B>foldUntil(G accum, Fn2<? super G,? super A,B> terminator, Fn2<? super G,? super A,G> reducer)
Thit implementation should be correct, but could be slow in the case where previous operations are slow and the terminateWhen operation is fast and terminates early.UnmodIterator<A>
iterator()
A one-time use, mutable, not-thread-safe way to get each value of the underling collection in turn.<B> Xform<B>
map(Fn1<? super A,? extends B> f)
Transform each item into exactly one new item using the given function.static <T> Xform<T>
of(java.lang.Iterable<? extends T> list)
Static factory methodsXform<A>
precat(java.lang.Iterable<? extends A> list)
Add items to the beginning of this Transformable ("precat" is a PREpending version of conCAT).Xform<A>
take(long numItems)
Return only the first n items.Xform<A>
takeWhile(Fn1<? super A,java.lang.Boolean> f)
Return items from the beginning until the given predicate returns false.protected abstract Xform.RunList
toRunList()
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Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
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Methods inherited from interface org.organicdesign.fp.xform.Transformable
toImList, toImMap, toImRrbt, toImSet, toImSortedMap, toImSortedSet, toMutableList, toMutableMap, toMutableRrbt, toMutableSet, toMutableSortedMap, toMutableSortedSet
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Methods inherited from interface org.organicdesign.fp.collections.UnmodIterable
head
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Field Detail
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EMPTY
public static final Xform EMPTY
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Method Detail
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empty
public static <T> Xform<T> empty()
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of
public static <T> Xform<T> of(java.lang.Iterable<? extends T> list)
Static factory methods
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iterator
public UnmodIterator<A> iterator()
Description copied from interface:UnmodIterable
A one-time use, mutable, not-thread-safe way to get each value of the underling collection in turn. I experimented with various thread-safe alternatives, but the JVM is optimized around iterators so this is the lowest common denominator of collection iteration, even though iterators are inherently mutable.- Specified by:
iterator
in interfacejava.lang.Iterable<A>
- Specified by:
iterator
in interfaceUnmodIterable<A>
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concat
public Xform<A> concat(java.lang.Iterable<? extends A> list)
Description copied from interface:UnmodIterable
Add items to the end of this Transformable (precat() adds to the beginning)- Specified by:
concat
in interfaceTransformable<A>
- Specified by:
concat
in interfaceUnmodIterable<A>
- Parameters:
list
- the items to add- Returns:
- a new Transformable with the items added.
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precat
public Xform<A> precat(java.lang.Iterable<? extends A> list)
Description copied from interface:UnmodIterable
Add items to the beginning of this Transformable ("precat" is a PREpending version of conCAT).- Specified by:
precat
in interfaceTransformable<A>
- Specified by:
precat
in interfaceUnmodIterable<A>
- Parameters:
list
- the items to add- Returns:
- a new Transformable with the items added.
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drop
public Xform<A> drop(long n)
The number of items to drop from the beginning of the output.- Specified by:
drop
in interfaceTransformable<A>
- Specified by:
drop
in interfaceUnmodIterable<A>
- Parameters:
n
- the number of items at the beginning of this Transformable to ignore- Returns:
- a Transformable with the specified number of items ignored.
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dropWhile
public Xform<A> dropWhile(Fn1<? super A,java.lang.Boolean> predicate)
The number of items to drop from the beginning of the output.- Specified by:
dropWhile
in interfaceTransformable<A>
- Specified by:
dropWhile
in interfaceUnmodIterable<A>
- Parameters:
predicate
- the predicate (test function)- Returns:
- a Transformable with the matching leading items ignored.
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fold
public <B> B fold(B ident, Fn2<? super B,? super A,B> reducer)
Provides a way to collect the results of the transformation.- Specified by:
fold
in interfaceTransformable<A>
- Specified by:
fold
in interfaceUnmodIterable<A>
- Parameters:
ident
- the accumulator and starting value. This will be passed to the function on the first iteration to be combined with the first member of the underlying data source. For some operations you'll need to pass an identity, e.g. for a sum, pass 0, for a product, pass 1 as this parameter.reducer
- combines each value in the list with the result so far. The initial result is u.- Returns:
- an eagerly evaluated result which could be a single value like a sum, or a collection.
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foldUntil
public <G,B> Or<G,B> foldUntil(G accum, Fn2<? super G,? super A,B> terminator, Fn2<? super G,? super A,G> reducer)
Thit implementation should be correct, but could be slow in the case where previous operations are slow and the terminateWhen operation is fast and terminates early. It actually renders items to a mutable List, then runs through the list performing the requested reduction, checking for early termination on the result. If you can to a takeWhile() or take() earlier in the transform chain instead of doing it here, always do that. If you really need early termination based on the *result* of a fold, and the operations are expensive or the input is huge, try using a View instead. If you don't care about those things, then this method is perfect for you. Normally you want to terminate by doing a take(), drop(), or takeWhile() before you get to the fold, but if you need to terminate based on the complete result so far, you can provide your own termination condition to this version of fold(). This function can do anything a loop can do. One use case is to accumulate a map and stop if it finds a duplicate key, before overwriting that element in the map. It could then return the map so far, an error, or whatever you like.- Specified by:
foldUntil
in interfaceTransformable<A>
- Specified by:
foldUntil
in interfaceUnmodIterable<A>
- Parameters:
accum
- the accumulator and starting value. This will be passed to the function on the first iteration to be combined with the first member of the underlying data source. For some operations you'll need to pass an identity, e.g. for a sum, pass 0, for a product, pass 1 as this parameter.terminator
- return null to continue processing. Return non-null to terminate the foldUntil and return Or.bad of this value. This function is called at the beginning of each "loop", thus it's first called with the original value of accum and the first item to process. Returning non-null immediately will prevent the reducer from ever being called.reducer
- combines each value in the list with the result so far. The initial result is u.- Returns:
- an
Or
where theOr.good()
is an eagerly evaluated result andOr.bad()
is whatever terminateWhen returned.
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filter
public Xform<A> filter(Fn1<? super A,java.lang.Boolean> f)
Description copied from interface:UnmodIterable
Return only the items for which the given predicate returns true.- Specified by:
filter
in interfaceTransformable<A>
- Specified by:
filter
in interfaceUnmodIterable<A>
- Parameters:
f
- a function that returns true for items to keep, false for items to drop- Returns:
- a Transformable of only the filtered items.
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flatMap
public <B> Xform<B> flatMap(Fn1<? super A,java.lang.Iterable<B>> f)
Description copied from interface:UnmodIterable
Transform each item into zero or more new items using the given function. One of the two higher-order functions that can produce more output items than input items. fold is the other, but flatMap is lazy while fold is eager.- Specified by:
flatMap
in interfaceTransformable<A>
- Specified by:
flatMap
in interfaceUnmodIterable<A>
- Parameters:
f
- yields a Transformable of 0 or more results for each input item.- Returns:
- a lazily evaluated collection which is expected to be larger than the input collection. For a collection that's the same size, map() is more efficient. If the expected return is smaller, use filter followed by map if possible, or vice versa if not.
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map
public <B> Xform<B> map(Fn1<? super A,? extends B> f)
Description copied from interface:UnmodIterable
Transform each item into exactly one new item using the given function.- Specified by:
map
in interfaceTransformable<A>
- Specified by:
map
in interfaceUnmodIterable<A>
- Parameters:
f
- a function that returns a new value for any value in the input- Returns:
- a Transformable of the same size as the input (may contain duplicates) containing the return values of the given function in the same order as the input values.
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toRunList
protected abstract Xform.RunList toRunList()
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take
public Xform<A> take(long numItems)
Description copied from interface:UnmodIterable
Return only the first n items.- Specified by:
take
in interfaceTransformable<A>
- Specified by:
take
in interfaceUnmodIterable<A>
- Parameters:
numItems
- the maximum number of items in the returned view.- Returns:
- a Transformable containing no more than the specified number of items.
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takeWhile
public Xform<A> takeWhile(Fn1<? super A,java.lang.Boolean> f)
Description copied from interface:UnmodIterable
Return items from the beginning until the given predicate returns false.- Specified by:
takeWhile
in interfaceTransformable<A>
- Specified by:
takeWhile
in interfaceUnmodIterable<A>
- Parameters:
f
- the predicate (test function)- Returns:
- a lazy transformable containing the longest un-interrupted run of items, from the beginning of the transformable, that satisfy the given predicate. This could be 0 items to the entire transformable.
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