feat: add thousands separator

.grit/patterns/thousands_separator.md

@@ -0,0 +1,76 @@
+---
+title: Add thousands separator
+---
+
+Add thousands separator (`1_000_000`) to numbers (ints and floats, positive or negative).
+
+```grit
+engine marzano(0.1)
+language python
+
+
+or { integer(), float() } as $number where {
+    or {
+        and {
+            $number <: r"(-?\d+)(\d{3})(\d{3})(\d{3})(\d{3})((?:\.\d+)?)$"($head, $g1, $g2, $g3, $g4, $fractional),
+            $groups = [$head, $g1, $g2, $g3, $g4],
+        },
+        and {
+            $number <: r"(-?\d+)(\d{3})(\d{3})(\d{3})((?:\.\d+)?)$"($head, $g1, $g2, $g3, $fractional),
+            $groups = [$head, $g1, $g2, $g3],
+        },
+        and {
+            $number <: r"(-?\d+)(\d{3})(\d{3})((?:\.\d+)?)$"($head, $g1, $g2, $fractional),
+            $groups = [$head, $g1, $g2],
+        },
+        and {
+            $number <: r"(-?\d+)(\d{3})((?:\.\d+)?)$"($head, $group, $fractional),
+            $groups = [$head, $group],
+        },
+    },
+    $formatted = join(list = $groups, separator = "_"),
+    $formatted = join(list = [$formatted, $fractional], separator = ""),
+} => `$formatted`
+```
+
+## Add thousands separator to number
+
+```python
+for n in range(1000):
+    pass
+
+n = -1000 - 2000
+n = 1000000000
+n = 123456789123456
+
+x = 1000.123
+x = 1000000000.123
+x = -123456789123456.123
+
+m = 1000000000000000
+
+# Left as is
+
+n = 999
+x = 999.0
+```
+
+```python
+for n in range(1_000):
+    pass
+
+n = -1_000 - 2_000
+n = 1_000_000_000
+n = 123_456_789_123_456
+
+x = 1_000.123
+x = 1_000_000_000.123
+x = -123_456_789_123_456.123
+
+m = 1000_000_000_000_000
+
+# Left as is
+
+n = 999
+x = 999.0
+```