added substring and simplified get function

For #7876 adds a Text.substring function which supports negative indexes and returns a part of a string from 0-based index 'start' and continuing for 'length'.

Also simplified get function as it looped unnecessarily.

distribution/lib/Standard/Base/0.0.0-dev/src/Data/Text/Extensions.enso

@@ -141,19 +141,14 @@ Text.at self index =
          "건반(Korean)".get 1 == "반"
 Text.get : Integer -> Any -> Any
 Text.get self index ~if_missing=Nothing =
-    case index < 0 of
-        True ->
-            length = self.length
-            new_index = index + length
-            if new_index < 0 then if_missing else
-                self.at new_index
-        False ->
-            iterator = BreakIterator.getCharacterInstance
-            iterator.setText self
-            first = iterator.next index
-            next = if first == -1 then -1 else iterator.next
-            if (next == -1) then if_missing else
-                Text_Utils.substring self first next
+    new_index = if index < 0 then index + self.length else index
+    if new_index < 0 then if_missing else
+        iterator = BreakIterator.getCharacterInstance
+        iterator.setText self
+        first = iterator.next new_index
+        next = if first == -1 then -1 else iterator.next
+        if (next == -1) then if_missing else
+            Text_Utils.substring self first next
 
 ## GROUP Selections
    Returns the first character from the text.
@@ -1791,19 +1786,6 @@ Text.parse_time_of_day self format:Date_Time_Formatter=Date_Time_Formatter.iso_t
 Text.parse_time_zone : Time_Zone ! Time_Error
 Text.parse_time_zone self = Time_Zone.parse self
 
-## PRIVATE
-   Returns the appropriate index for a text object given a negative index.
-   If positive returns index.
-Text.get_position : Integer -> Integer
-Text.get_position self index ~if_missing=Nothing =
-    case index < 0 of
-        True ->
-            length = self.length
-            new_index = index + length
-            if new_index < 0 then if_missing else
-                self.get_position new_index
-        False ->
-            index
 ## ALIAS mid, slice, substring
    GROUP Selections
    Creates a new Text by selecting the specified range of the input.
@@ -1825,11 +1807,13 @@ Text.get_position self index ~if_missing=Nothing =
 
 Text.substring : Integer -> Integer -> Range ! Index_Out_Of_Bounds
 Text.substring self start:Integer length:Integer=self.length =
-    if length <= 0 then Error.throw (Illegal_Argument.Error "length must be greater than 0") else
-        fixed_start = self.get_position start
-        if fixed_start == Nothing then Error.throw (Illegal_Argument.Error "negative start was greater than the total number of characters") else
-            range = fixed_start.up_to fixed_start+length
-            self.take range
+    if length < 0 then Error.throw (Illegal_Argument.Error "length must be greater than or equal to 0") else
+        if length == 0 then "" else
+            self_length = self.length
+            fixed_start = if start < 0 then start + self_length else start
+            if fixed_start < 0 then (Error.throw (Index_Out_Of_Bounds.Error start self.length)) else
+                range = fixed_start.up_to fixed_start+length
+                self.take range
 
 ## PRIVATE
    Returns a new Text constructed by slicing the input according to the provided

test/Tests/src/Data/Text_Spec.enso

@@ -186,10 +186,6 @@ spec =
             str.get 1 . should_equal facepalm
             str.get 2 . should_equal accent_1
             str.get 3 . should_equal accent_2
-            str.get_position 0 . should_equal 0
-            str.get_position 1 . should_equal 1
-            str.get_position 2 . should_equal 2
-            str.get_position 3 . should_equal 3
             str.first . should_equal kshi
             str.second . should_equal facepalm
             str.last . should_equal accent_2
@@ -204,10 +200,6 @@ spec =
             str.get -3 . should_equal facepalm
             str.get -2 . should_equal accent_1
             str.get -1 . should_equal accent_2
-            str.get_position -4 . should_equal 0
-            str.get_position -3 . should_equal 1
-            str.get_position -2 . should_equal 2
-            str.get_position -1 . should_equal 3
 
         Test.specify "should return a dataflow error when accessing characters out of bounds" <|
             str = kshi + facepalm + accent_1 + accent_2
@@ -218,9 +210,6 @@ spec =
             str.get -5 . should_equal Nothing
             str.get 4 . should_equal Nothing
             str.get -5 "?" . should_equal "?"
-            str.get_position -5 . should_equal Nothing
-            str.get_position 4 . should_equal Nothing
-            str.get_position -5 "?" . should_equal "?"
             "".first.should_fail_with Index_Out_Of_Bounds
             "".second.should_fail_with Index_Out_Of_Bounds
             "".last.should_fail_with Index_Out_Of_Bounds
@@ -1665,11 +1654,10 @@ spec =
             "Hello World!".substring 5 7 . should_equal " World!"
             "Hello World!".substring -7 3 . should_equal " Wo"
 
-        Test.specify "should error on length 0 or less" <|
-            "Hello World!".substring 5 0 . should_fail_with Illegal_Argument
+        Test.specify "should error on length less than 0" <|
             "Hello World!".substring 5 -2 . should_fail_with Illegal_Argument
 
         Test.specify "should error if negative start index is too large"
-            "Hello World!".substring -20 5 . should_fail_with Illegal_Argument
+            "Hello World!".substring -20 5 . should_fail_with Index_Out_Of_Bounds
 
 main = Test_Suite.run_main spec