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Data analysts should be able to reverse strings using Text.reverse #3377

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merged 4 commits into from
Apr 5, 2022
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Data analysts should be able to reverse strings using Text.reverse #3377

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7b283f3
feat: Add `Text.reverse` extension for string reversal
indiv0 Apr 4, 2022
221a588
style: Add missing whitespace to documentation example for `Text.reve…
indiv0 Apr 5, 2022
2b9425f
style: Indent code block to 4 spaces relative to caption
indiv0 Apr 5, 2022
b6b004f
Merge branch 'develop' into wip/npekin/text-reverse-181265419
indiv0 Apr 5, 2022
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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -92,6 +92,7 @@
- [Added warning handling to `Table.aggregate`][3349]
- [Improved performance of `Table.aggregate` and full warnings implementation]
[3364]
- [Implemented `Text.reverse`][3377]

[debug-shortcuts]:
https://github.com/enso-org/enso/blob/develop/app/gui/docs/product/shortcuts.md#debug
Expand Down Expand Up @@ -140,6 +141,7 @@
[3349]: https://github.com/enso-org/enso/pull/3349
[3361]: https://github.com/enso-org/enso/pull/3361
[3364]: https://github.com/enso-org/enso/pull/3364
[3377]: https://github.com/enso-org/enso/pull/3377

#### Enso Compiler

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23 changes: 23 additions & 0 deletions distribution/lib/Standard/Base/0.0.0-dev/src/Data/Text/Extensions.enso
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Expand Up @@ -25,6 +25,7 @@ export Standard.Base.Data.Text.Line_Ending_Style

polyglot java import com.ibm.icu.lang.UCharacter
polyglot java import com.ibm.icu.text.BreakIterator
polyglot java import java.lang.StringBuilder
polyglot java import org.enso.base.Text_Utils

## UNSTABLE
Expand Down Expand Up @@ -58,6 +59,28 @@ Text.length =
@Tail_Call count (accum + 1) iterator.next
count 0 iterator.next

## Returns a new `Text` object with the characters in the reverse order of the input.

! What is a Character?
A character is defined as an Extended Grapheme Cluster, see Unicode
Standard Annex 29. This is the smallest unit that still has semantic
meaning in most text-processing applications.

> Example
Reverse the text "Hello, world!".
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"Hello, world!".reverse
Text.reverse : Text
Text.reverse =
reverseStringBuilder = StringBuilder.new this.length
iterator = BreakIterator.getCharacterInstance
iterator.setText this

iterate prev next = if next == -1 then reverseStringBuilder.toString else
reverseStringBuilder.append (Text_Utils.substring this next prev)
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Using a StringBuilder works, but I'm wondering if using our + wouldn't be more idiomatic - for example our Vector.join does in fact use +.

Performance-wise it should be quite comparable, because our + uses ropes under the hood to achieve O(1) amortized append time. Still, probably StringBuilder has a bit less of an overhead, so likely still a bit faster.

So I'm not really saying to change it - because this definitely works and is fast, but wondering what best practices we should adopt - because I think it would be good to have consistent approach to this between this function, Vector.join and possibly other ones.

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Yes, Text ropes cache collapsed strings - see ToJavaStringNode::inplaceFlatten.

As for Vector.join - I'm talking about the function which concatenates a vector of texts into a single text, did you mean Vector.+ instead?

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@indiv0 indiv0 Apr 5, 2022 •
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Idiomatically, + does seem like the right choice.

When I was implementing this, I actually did compare both approaches and the + was ~2-3x slower for a 10000 length string. Though that may be due to me making some other error in the implementation. I can re-draft that benchmark and include it in the PR if you'd like to compare for yourself. I didn't include the benchmark in the commit because it didn't seem like this is something likely to change, performance-wise, over time.

Not sure if I follow the Vector.join and Vector.+ comments.

StringBuilder impl:

Text.reverse 10000 characters/iteration:0: 595.53ms                                                                                                                                     
Text.reverse 10000 characters/iteration:1: 405.00ms                                                                                                                                     
Text.reverse 10000 characters/iteration:2: 402.30ms                                                                                                                                     
Text.reverse 10000 characters/iteration:3: 402.01ms                                                                                                                                     
Text.reverse 10000 characters/iteration:4: 400.68ms                                                                                                                                     
Text.reverse 10000 characters/iteration:5: 401.56ms                                                                                                                                     
Text.reverse 10000 characters/iteration:6: 409.98ms                                                                                                                                     
Text.reverse 10000 characters/iteration:7: 417.73ms                                                                                                                                     
Text.reverse 10000 characters/iteration:8: 408.80ms                                                                                                                                     
Text.reverse 10000 characters/iteration:9: 400.80ms

+ impl:

Text.reverse 10000 characters/iteration:0: 1083.13ms                                        
Text.reverse 10000 characters/iteration:1: 1274.55ms                                        
Text.reverse 10000 characters/iteration:2: 1267.65ms                                        
Text.reverse 10000 characters/iteration:3: 1195.36ms                                        
Text.reverse 10000 characters/iteration:4: 1140.85ms                                        
Text.reverse 10000 characters/iteration:5: 1167.93ms                                        
Text.reverse 10000 characters/iteration:6: 1162.50ms                                        
Text.reverse 10000 characters/iteration:7: 1199.97ms                                        
Text.reverse 10000 characters/iteration:8: 1203.35ms                                        
Text.reverse 10000 characters/iteration:9: 1242.65ms

Naive (StringBuilder.new this).reverse (not really a fair comparison because not extended-grapheme-cluster-aware):

Text.reverse 10000 characters/iteration:0: 6.57ms                                           
Text.reverse 10000 characters/iteration:1: 3.47ms                                           
Text.reverse 10000 characters/iteration:2: 3.96ms                                           
Text.reverse 10000 characters/iteration:3: 3.45ms                                           
Text.reverse 10000 characters/iteration:4: 4.05ms                                           
Text.reverse 10000 characters/iteration:5: 4.81ms                                           
Text.reverse 10000 characters/iteration:6: 6.69ms                                           
Text.reverse 10000 characters/iteration:7: 6.56ms                                           
Text.reverse 10000 characters/iteration:8: 7.33ms                                           
Text.reverse 10000 characters/iteration:9: 8.02ms

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@radeusgd ping ^

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Hmm, then I think you are right that it may be better to keep the stringbuilder. I guess the difference is because the ropes still have some more allocation overhead.

As for Vector.join and Vector.+ - no worry it was a reply to a later deleted comment, please ignore 😅

@Tail_Call iterate next iterator.previous
iterate iterator.last iterator.previous

## Applies the provided `function` to each character in `this`.

Arguments:
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11 changes: 11 additions & 0 deletions test/Tests/src/Data/Text_Spec.enso
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Expand Up @@ -496,6 +496,17 @@ spec =
str.at -6 . should_fail_with Index_Out_Of_Bounds_Error
str.at 5 . should_fail_with Index_Out_Of_Bounds_Error

Test.specify "should be able to reverse characters" <|
"Hello World!".reverse . should_equal "!dlroW olleH"

"".reverse . should_equal ""
'e\u{301}'.reverse . should_equal 'e\u{301}'
'e\u{301}\u00E9'.reverse . should_equal '\u00E9e\u{301}'
'e\u{321}\u{360}'.reverse . should_equal 'e\u{321}\u{360}'
'Iñtërnâtiônàlizætiøn☃💩'.reverse . should_equal '💩☃nøitæzilànôitânrëtñI'
'ほげほげ'.reverse . should_equal 'げほげほ'
'\u{10000}'.reverse . should_equal '\u{10000}'

Test.specify "should allow to iterate over characters" <|
str = kshi + accent_1 + accent_2 + 'abc'
builder = Vector.new_builder
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