start new implementation

.gitignore

@@ -6,4 +6,5 @@ examples/simple
 generated-docs
 package/InternalGBPGen
 package/GraphemeTestGen
+package/GraphemeTestGen2
 package/InternalEmojiGen

package/Grapheme2.roc

@@ -0,0 +1,88 @@
+interface Grapheme2
+    exposes [
+        Grapheme,
+        split,
+    ]
+    imports [
+        CodePoint.{ CodePoint, Utf8ParseErr },
+        InternalGBP.{ GBP },
+        InternalCP.{fromU32Unchecked},
+        InternalEmoji,
+    ]
+
+## Extended Grapheme Cluster
+Grapheme : InternalGBP.GBP
+
+## Split a string into extended grapheme clusters
+split : Str -> Result (List Str) Utf8ParseErr
+split = \str ->
+
+    # Note I'm not sure if we should return an error here or just crash. 
+    # A Roc Str should be be valid utf8 and so in theory it should not be possible 
+    # for split to have invalid utf8 in it. To be discussed.
+    codePoints <- str |> Str.toUtf8 |> CodePoint.parseUtf8 |> Result.map
+
+    breakPoints = codePoints |> List.map InternalGBP.fromCP
+
+    splitHelp Start codePoints breakPoints |> toListStr
+
+# Refer to https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundary_Rules
+Rule : [GB1, GB2, GB3, GB4, GB5, GB6, GB7, GB8, GB9, GB9a, GB9b, GB9c, GB11, GB12, GB13, GB999]
+
+OutState : List [
+    BR Rule,
+    NB Rule, 
+    CP CodePoint,
+]
+
+toListStr : OutState -> List Str 
+toListStr = \outState ->
+    List.walk outState { acc : [], cps : [] } \state, curr ->
+        when curr is 
+            NB _ -> state 
+            BR _ -> { acc : [], cps: List.append state.cps state.acc}
+            CP cp -> { acc : List.append state.acc cp, cps: state.cps}
+    |> .cps
+    |> List.map \cpList -> 
+        # Again I'm not sure if we should crash here... I dont think CodePoint.toStr
+        # should be returning a result... to be discussed.
+        when CodePoint.toStr cpList is 
+            Ok str -> str
+            Err _ -> crash "unreachable got invalid utf8 when converting CodePoints to Str"
+
+splitHelp : State, List CodePoint, List GBP -> OutState
+splitHelp = \state, codePoints, breakPoints ->
+    next = List.dropFirst combined 1
+    when (state, code) is 
+        [] -> [BR GB2] # base case
+        [T cp _, ..] -> List.concat [CP cp, BR GB999] (splitHelp next) 
+
+State : [
+    Start,
+]
+
+expect 
+    a = testHelp "abc"
+    b = [
+        BR GB1, 
+        CP (cpFromU8 'a'), 
+        BR GB999, 
+        CP (cpFromU8 'b'), 
+        BR GB999, 
+        CP (cpFromU8 'c'), 
+        BR GB999, 
+        BR GB2,
+    ]
+    a == b
+
+
+cpFromU8 : U8 -> CodePoint
+cpFromU8 = \b -> b |> Num.toU32 |> fromU32Unchecked
+
+testHelp : Str -> OutState
+testHelp = \str -> 
+    when str |> Str.toUtf8 |> CodePoint.parseUtf8 is 
+        Err _ -> crash "expected valid Utf8"
+        Ok codePoints -> 
+            breakPoints = (List.map codePoints InternalGBP.fromCP)
+            splitHelp Start codecodePoints breakPoints