# Pipelined filters and operations on iterators.
#
-# This module enhance `Collection`s with some methods that enable a
-# pipeline-like programing that offers the manupulation of
-# collections trough connected filters with reasonable memory constraints.
-#
-# The filters methods return a view bounded on the original collection.
-# Filters can be chained to build complex virtual collections.
-#
-# FIXME: Fix vocabulary (lazy/view/filter)
-# FIXME: Maybe the name of the method should indicate that the method is 'lazy' (or is a filter).
+# This module enhances `Iterator` with some methods that enable a pipeline-like programing.
+# The processing of elements in a pipeline is done trough connected filters that are implemented with reasonable memory constraints.
module pipeline
-redef interface Collection[E]
- # Filter: sort with ComparableSorter.
+redef interface Iterator[E]
+ # Filter: sort with `default_comparator`.
# SEE: `sort_with` for details
# REQUIRE: self isa Iterator[Comparable]
#
- # assert [1,3,2].sort_filter.to_a == [1,2,3]
- fun sort_filter: Collection[E]
+ # assert [1,3,2].iterator.sort.to_a == [1,2,3]
+ fun sort: Iterator[E]
do
- assert self isa Collection[Comparable]
- var sorter = new ComparableSorter[Comparable]
+ assert self isa Iterator[Comparable]
var a = self.to_a
- sorter.sort(a)
- return a
+ default_comparator.sort(a)
+ return a.iterator
end
- # Filter: sort with a given `sorter`.
+ # Filter: sort with a given `comparator`.
# Important: require O(n) memory.
- fun sort_with(sorter: AbstractSorter[E]): Collection[E]
+ #
+ # assert ["a", "c", "b"].iterator.sort_with(alpha_comparator).to_a == ["a", "b", "c"]
+ fun sort_with(comparator: Comparator): Iterator[E]
do
var a = self.to_a
- sorter.sort(a)
- return a
+ comparator.sort(a)
+ return a.iterator
end
# Filter: reject duplicates.
# Important: rely on `==` and `hash`
# Important: require O(m) in memory, where m is the total number of uniq items.
#
- # assert [1,2,1,1,1,3,2].uniq.to_a == [1,2,3]
+ # assert [1,2,1,1,1,3,2].iterator.uniq.to_a == [1,2,3]
#
# REQUIRE: self isa Iterator[Object]
- fun uniq: Collection[E]
+ fun uniq: Iterator[E]
do
- assert self isa Collection[Object]
+ assert self isa Iterator[Object]
return new PipeUniq[E](self)
end
#
# Important: rely on `==`.
#
- # assert [1,2,1,1,1,3,2].seq_uniq.to_a == [1,2,1,3,2]
- fun seq_uniq: Collection[E]
+ # assert [1,2,1,1,1,3,2].iterator.seq_uniq.to_a == [1,2,1,3,2]
+ fun seq_uniq: Iterator[E]
do
return new PipeSeqUniq[E](self)
end
- # The view of two combined collections.
+ # Combine two iterators.
+ #
+ # When the first iterator is terminated, the second is started.
#
- # assert ([1..20[ + [20..40[).to_a == ([1..40[).to_a
- fun +(other: Collection[E]): Collection[E]
+ # assert ([1..20[.iterator + [20..40[.iterator).to_a == ([1..40[).to_a
+ fun +(other: Iterator[E]): Iterator[E]
do
return new PipeJoin[E](self, other)
end
# Alternate each item with `e`.
#
- # assert [1,2,3].alternate(0).to_a == [1,0,2,0,3]
- fun alternate(e: E): Collection[E]
+ # assert [1,2,3].iterator.alternate(0).to_a == [1,0,2,0,3]
+ fun alternate(e: E): Iterator[E]
do
return new PipeAlternate[E](self, e)
end
# Filter: reject a given `item`.
#
- # assert [1,1,2,1,3].skip(1).to_a == [2,3]
- fun skip(item: E): Collection[E]
+ # assert [1,1,2,1,3].iterator.skip(1).to_a == [2,3]
+ fun skip(item: E): Iterator[E]
do
return new PipeSkip[E](self, item)
end
# Filter: keep only the first `length` items.
#
- # assert [1,2,3,4,5].head(2).to_a == [1,2]
- fun head(length: Int): Collection[E]
+ # This filter does not always consume `self'.
+ #
+ # var i = [1,2,3,4,5].iterator
+ # assert i.head(2).to_a == [1,2]
+ # assert i.to_a == [3,4,5]
+ fun head(length: Int): Iterator[E]
do
return new PipeHead[E](self, length)
end
# Filter: reject the first `length` items.
#
- # assert [1,2,3,4,5].skip_head(2).to_a == [3,4,5]
+ # assert [1,2,3,4,5].iterator.skip_head(2).to_a == [3,4,5]
#
# ENSURE: self == return
- fun skip_head(length: Int): Collection[E]
+ fun skip_head(length: Int): Iterator[E]
do
- return new PipeSkipHead[E](self, length)
+ while length > 0 and self.is_ok do
+ length -= 1
+ self.next
+ end
+ return self
end
# Filter: keep only the last `length` items.
#
- # assert [1,2,3,4,5].tail(2).to_a == [4,5]
+ # assert [1,2,3,4,5].iterator.tail(2).to_a == [4,5]
#
# Important: require O(length) in memory
- fun tail(length: Int): Collection[E]
+ fun tail(length: Int): Iterator[E]
do
- return new PipeTail[E](self, length)
+ var lasts = new List[E]
+ while self.is_ok do
+ while lasts.length >= length do lasts.shift
+ lasts.push(self.item)
+ self.next
+ end
+ return lasts.iterator
end
# Filter: reject the last `length` items.
#
- # assert [1,2,3,4,5].skip_tail(2).to_a == [1,2,3]
+ # assert [1,2,3,4,5].iterator.skip_tail(2).to_a == [1,2,3]
#
# Important: require O(length) in memory
- fun skip_tail(length: Int): Collection[E]
+ fun skip_tail(length: Int): Iterator[E]
do
return new PipeSkipTail[E](self, length)
end
+
+ # Filter: reject items that does not meet some criteria.
+ #
+ # class IsEvenFunction
+ # super Function[Int, Bool]
+ # redef fun apply(i) do return i % 2 == 0
+ # end
+ # assert [1,2,3,4,8].iterator.select(new IsEvenFunction).to_a == [2,4,8]
+ fun select(predicate: Function[E, Bool]): Iterator[E]
+ do
+ return new PipeSelect[E](self, predicate)
+ end
end
-### Specific private collection and iterator classes
+# Wraps an iterator to skip nulls.
+#
+# ~~~nit
+# var i: Iterator[Int]
+#
+# i = new NullSkipper[Int]([null, 1, null, 2, null: nullable Int].iterator)
+# assert i.to_a == [1, 2]
+#
+# i = new NullSkipper[Int]([1, null, 2, 3: nullable Int].iterator)
+# assert i.to_a == [1, 2, 3]
+# ~~~
+class NullSkipper[E: Object]
+ super Iterator[E]
-private class PipeUniq[E]
- super NaiveCollection[E]
- var source: Collection[E]
- redef fun iterator do return new PipeUniqIterator[E](source.iterator)
+ # The inner iterator.
+ var inner: Iterator[nullable E]
+
+ redef fun finish do inner.finish
+
+ redef fun is_ok do
+ skip_nulls
+ return inner.is_ok
+ end
+
+ redef fun item do
+ skip_nulls
+ return inner.item.as(E)
+ end
+
+ redef fun next do
+ inner.next
+ skip_nulls
+ end
+
+ private fun skip_nulls do
+ while inner.is_ok and inner.item == null do inner.next
+ end
+end
+
+# Interface that reify a function.
+# Concrete subclasses must implements the `apply` method.
+#
+# This interface helps to manipulate function-like objects.
+#
+# The main usage it as a transformation; that takes an argument and produce a result.
+# See `map` for example.
+#
+# Another usage is as a predicate, with `Function[E, Bool]`.
+# See `Iterator::select` for example.
+#
+# Function with more than one argument can be reified with some uncurification.
+# Eg. `Function[ARG1, Function[ARG2, RES]]`.
+#
+# NOTE: Nit is not a functionnal language, this class is a very basic way to
+# simulate the reification of a simple function.
+interface Function[FROM, TO]
+ # How an element is mapped to another one.
+ fun apply(e: FROM): TO is abstract
+
+ # Filter: produce an iterator which each element is transformed.
+ #
+ # var i = [1,2,3].iterator
+ # assert fun_to_s.map(i).to_a == ["1", "2", "3"]
+ #
+ # Note: because there is no generic method in Nit (yet?),
+ # there is no way to have a better API.
+ # eg. with the Iterator as receiver and the function as argument.
+ # (see `Iterator::select`)
+ fun map(i: Iterator[FROM]): Iterator[TO]
+ do
+ return new PipeMap[FROM, TO](i, self)
+ end
+end
+
+private class FunctionToS
+ super Function[Object, String]
+ redef fun apply(e) do return e.to_s
end
-private class PipeUniqIterator[E]
+### Specific private iterator classes
+
+private class PipeUniq[E]
super Iterator[E]
var source: Iterator[E]
end
private class PipeSeqUniq[E]
- super NaiveCollection[E]
- var source: Collection[E]
- redef fun iterator do return new PipeSeqUniqIterator[E](source.iterator)
-end
-
-private class PipeSeqUniqIterator[E]
super Iterator[E]
var source: Iterator[E]
end
private class PipeJoin[E]
- super NaiveCollection[E]
- var source1: Collection[E]
- var source2: Collection[E]
- redef fun iterator do return new PipeJoinIterator[E](source1.iterator, source2.iterator)
-end
-
-private class PipeJoinIterator[E]
super Iterator[E]
var source1: Iterator[E]
var source2: Iterator[E]
end
private class PipeAlternate[E]
- super NaiveCollection[E]
- var source: Collection[E]
- var odd_item: E
- redef fun iterator do return new PipeAlternateIterator[E](source.iterator, odd_item)
-end
-
-private class PipeAlternateIterator[E]
super Iterator[E]
var source: Iterator[E]
end
private class PipeSkip[E]
- super NaiveCollection[E]
- var source: Collection[E]
- var skip_item: E
- redef fun iterator do return new PipeSkipIterator[E](source.iterator, skip_item)
-end
-
-private class PipeSkipIterator[E]
- super NaiveCollection[E]
super Iterator[E]
var source: Iterator[E]
var skip_item: E
- init(source: Iterator[E], skip_item: E)
- do
- self.source = source
- self.skip_item = skip_item
-
- do_skip
- end
+ init do do_skip
fun do_skip
do
end
private class PipeHead[E]
- super NaiveCollection[E]
- var source: Collection[E]
- var pipe_length: Int
- redef fun iterator do return new PipeHeadIterator[E](source.iterator, pipe_length)
-end
-
-private class PipeHeadIterator[E]
super Iterator[E]
var source: Iterator[E]
end
end
-private class PipeSkipHead[E]
- super NaiveCollection[E]
- var source: Collection[E]
- var pipe_length: Int
- redef fun iterator
- do
- var res = source.iterator
- var length = pipe_length
- while length > 0 and res.is_ok do
- length -= 1
- res.next
- end
- return res
- end
-end
-
-private class PipeTail[E]
- super NaiveCollection[E]
- var source: Collection[E]
- var pipe_length: Int
- redef fun iterator
- do
- var lasts = new List[E]
- var res = source.iterator
- var length = pipe_length
- while res.is_ok do
- while lasts.length >= length do lasts.shift
- lasts.push(res.item)
- res.next
- end
- return lasts.iterator
- end
-end
-
private class PipeSkipTail[E]
- super NaiveCollection[E]
- var source: Collection[E]
- var pipe_length: Int
- redef fun iterator do return new PipeSkipTailIterator[E](source.iterator, pipe_length)
-end
-
-private class PipeSkipTailIterator[E]
super Iterator[E]
var source: Iterator[E]
var lasts = new List[E]
- init(source: Iterator[E], length: Int)
+ init
do
- self.source = source
- self.length = length
var lasts = self.lasts
while source.is_ok and lasts.length < length do
lasts.push(source.item)
source.next
end
end
+
+private class PipeSelect[E]
+ super Iterator[E]
+
+ var source: Iterator[E]
+
+ var predicate: Function[E, Bool]
+
+ init do do_skip
+
+ fun do_skip
+ do
+ while source.is_ok and not predicate.apply(source.item) do source.next
+ end
+
+ redef fun is_ok do return source.is_ok
+
+ redef fun item do return source.item
+
+ redef fun next
+ do
+ source.next
+ do_skip
+ end
+end
+
+private class PipeMap[E, F]
+ super Iterator[F]
+
+ var source: Iterator[E]
+ var function: Function[E, F]
+
+ var item_cache: nullable F = null
+ var item_cached = false
+
+ redef fun is_ok do return source.is_ok
+
+ redef fun item do
+ if item_cached then return item_cache
+ item_cache = function.apply(source.item)
+ item_cached = true
+ return item_cache
+ end
+
+ redef fun next do
+ source.next
+ item_cached = false
+ end
+end
+
+# Stateless singleton that reify to the `to_s` method.
+#
+# assert fun_to_s.apply(5) == "5"
+fun fun_to_s: Function[Object, String] do return once new FunctionToS
nitlanguage / nit.git / blobdiff