feat:allow other kinds of unicode space as digit group separators

Based on feedback in chat, I added support for several more kinds of
Unicode space character for separating digit groups, both when reading
and when displaying numbers. These are the spaces currently supported,
which are just my best guess at the ones that might show up in CSV files
now and then:

space,
no-break space,
en space,
em space,
punctuation space,
thin space,
narrow no-break space,
medium mathematical space

hledger-lib/Hledger/Read/Common.hs

@@ -1169,7 +1169,20 @@ rawnumberp = label "number" $ do
     pure $ NoSeparators grp1 (Just (decPt, mempty))
 
 isDigitSeparatorChar :: Char -> Bool
-isDigitSeparatorChar c = isDecimalMark c || c == ' '
+isDigitSeparatorChar c = isDecimalMark c || isDigitSeparatorSpaceChar c
+
+-- | Kinds of unicode space character we accept as digit group marks.
+-- See also https://en.wikipedia.org/wiki/Decimal_separator#Digit_grouping .
+isDigitSeparatorSpaceChar :: Char -> Bool
+isDigitSeparatorSpaceChar c =
+     c == ' '  -- space
+  || c == ' '  -- no-break space
+  || c == ' '  -- en space
+  || c == ' '  -- em space
+  || c == ' '  -- punctuation space
+  || c == ' '  -- thin space
+  || c == ' '  -- narrow no-break space
+  || c == ' '  -- medium mathematical space
 
 -- | Some kinds of number literal we might parse.
 data RawNumber

hledger/hledger.m4.md

@@ -1200,13 +1200,23 @@ A *decimal mark* can be written as a period or a comma:
     1,23
 
 In the integer part of the quantity (left of the decimal mark), groups
-of digits can optionally be separated by a *digit group mark* - a
+of digits can optionally be separated by a *digit group mark* -
-space, comma, or period (different from the decimal mark):
+a comma or period (whichever is not used as decimal mark), 
+or a space (any of these Unicode space characters:
+space,
+no-break space,
+en space,
+em space,
+punctuation space,
+thin space,
+narrow no-break space,
+medium mathematical space).
 
          $1,000,000.00
       EUR 2.000.000,00
     INR 9,99,99,999.00
-          1 000 000.9455
+          1 000 000.00   <- ordinary space  
+          1 000 000.00   <- no-break space
 
 hledger is not biased towards [period or comma decimal marks][international number formats],
 so a number containing just one period or comma, like `1,000` or `1.000`, is ambiguous.

hledger/test/journal/numbers.test

@@ -36,14 +36,27 @@ $ hledger bal -f -
 >2 //
 >= 1
 
-# ** 5. Space between digits groups
+# ** 5. Spaces between digit groups, any of the 8 unicode space characters we support.
 <
-2017/1/1
+2000-01-01
-	a   1 000.00 EUR
+  (a)  1 000. A  ; space                    
-	b  -1 000.00 EUR
+  (b)  1 000. B  ; no-break space           
-$ hledger bal -f - --no-total
+  (c)  1 000. C  ; en space                 
-        1 000.00 EUR  a
+  (d)  1 000. D  ; em space                 
-       -1 000.00 EUR  b
+  (e)  1 000. E  ; punctuation space        
+  (f)  1 000. F  ; thin space               
+  (g)  1 000. G  ; narrow no-break space    
+  (h)  1 000. H  ; medium mathematical space
+
+$ hledger bal -f - -N
+             1 000 A  a
+             1 000 B  b
+             1 000 C  c
+             1 000 D  d
+             1 000 E  e
+             1 000 F  f
+             1 000 G  g
+             1 000 H  h
 
 # ** 6. Space between digits groups in commodity directive
 <
@@ -203,3 +216,24 @@ Balance changes in 2021:
 ===++===================================
  a || -0.12345678901234567890123456 EUR 
 
+# ** 21. When spaces are used inconsistently, what happens ? The usual, first one seen sets commodity style.
+<
+2000-01-01
+  (a)  1 000. A  ; no-break space           
+  (a)  1 000. A  ; space                    
+  (a)  1 000. A  ; en space                 
+
+$ hledger bal -f - -N
+             3 000 A  a
+
+# ** 22. And a commodity directive can enforce consistency as usual.
+<
+commodity 1 000. A  ; narrow no-break space
+
+2000-01-01
+  (a)  1 000. A  ; space                    
+  (a)  1 000. A  ; no-break space           
+  (a)  1 000. A  ; en space                 
+
+$ hledger bal -f - -N
+             3 000 A  a