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Use deferred execution for Sequence.map and Sequence.where

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The methods Sequence.map and Sequence.where are now implemented using
deferred execution. They return an instance of a new Sequence-derived
class that performs the operation while iterating. This has three main
advantages:

* It can be computationally cheaper when not the whole sequence is
  iterated.

* It consumes less memory since it does not store the result in a newly
  allocated list.

* They can work on infinite sequences.

Some disadvantages are:

* Iterating the returned iterator will be slightly slower due to
  the added indirection.

* You should be aware that modifications made to the original sequence
  will affect the returned sequence.

* If you need the result in a list, you now need to call Sequence.list
  on the result.
This commit is contained in:
Thorbjørn Lindeijer
2015-03-31 22:25:07 +02:00
parent a7fafce265
commit a8ea2a91a6
9 changed files with 160 additions and 44 deletions
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src/vm/wren_core.c
+28 -14
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@@ -72,21 +72,9 @@ static const char* libSource =
" return result\n"
" }\n"
"\n"
" map(f) {\n"
" var result = new List\n"
" for (element in this) {\n"
" result.add(f.call(element))\n"
" }\n"
" return result\n"
" }\n"
" map(transformation) { new MapSequence(this, transformation) }\n"
"\n"
" where(f) {\n"
" var result = new List\n"
" for (element in this) {\n"
" if (f.call(element)) result.add(element)\n"
" }\n"
" return result\n"
" }\n"
" where(predicate) { new WhereSequence(this, predicate) }\n"
"\n"
" all(f) {\n"
" for (element in this) {\n"
@@ -146,6 +134,32 @@ static const char* libSource =
" }\n"
"}\n"
"\n"
"class MapSequence is Sequence {\n"
" new(seq, f) {\n"
" _seq = seq\n"
" _f = f\n"
" }\n"
"\n"
" iterate(n) { _seq.iterate(n) }\n"
" iteratorValue(iterator) { _f.call(_seq.iteratorValue(iterator)) }\n"
"}\n"
"\n"
"class WhereSequence is Sequence {\n"
" new(seq, f) {\n"
" _seq = seq\n"
" _f = f\n"
" }\n"
"\n"
" iterate(n) {\n"
" while (n = _seq.iterate(n)) {\n"
" if (_f.call(_seq.iteratorValue(n))) break\n"
" }\n"
" return n\n"
" }\n"
"\n"
" iteratorValue(iterator) { _seq.iteratorValue(iterator) }\n"
"}\n"
"\n"
"class String is Sequence {\n"
" bytes { new StringByteSequence(this) }\n"
"}\n"