Merge: Extend is_numeric to support negative values and scientific notation

Pull-Request: #1917
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Jean Privat <jean@pryen.org>

Author: privat

lib/core/text/abstract_text.nit

@@ -305,26 +305,32 @@ abstract class Text
 		end
 	end
 
-	# Returns `true` if the string contains only Numeric values (and one "," or one "." character)
+	# Is this string in a valid numeric format compatible with `to_f`?
 	#
 	#     assert "123".is_numeric  == true
 	#     assert "1.2".is_numeric  == true
-	#     assert "1,2".is_numeric  == true
+	#     assert "-1.2".is_numeric == true
+	#     assert "-1.23e-2".is_numeric == true
 	#     assert "1..2".is_numeric == false
+	#     assert "".is_numeric     == false
 	fun is_numeric: Bool
 	do
-		var has_point_or_comma = false
+		var has_point = false
+		var e_index = -1
 		for i in [0..length[ do
 			var c = chars[i]
 			if not c.is_numeric then
-				if (c == '.' or c == ',') and not has_point_or_comma then
-					has_point_or_comma = true
+				if c == '.' and not has_point then
+					has_point = true
+				else if c == 'e' and e_index == -1 and i > 0 and i < length - 1 and chars[i-1] != '-' then
+					e_index = i
+				else if c == '-' and i == e_index + 1 and i < length - 1 then
 				else
 					return false
 				end
 			end
 		end
-		return true
+		return not is_empty
 	end
 
 	# Returns `true` if the string contains only Hex chars

tests/sav/test_string_is_numeric.res

@@ -1,7 +1,7 @@
 false
 true
 true
-true
+false
 false
 false
 false

tests/test_string_is_numeric.nit

@@ -25,7 +25,7 @@ print "45".is_numeric
 #True
 print "45.3".is_numeric
 
-#True
+#False
 print "45,3".is_numeric
 
 #False