fix: support comma as decimal separator (ISO 8601 European format) (#11)

Add support for comma (,) as a decimal separator in fractional seconds
for both time and duration components, as specified in ISO 8601.

Changes:
- Parser now accepts both . and , as decimal separators
- Stringify normalizes all output to canonical . notation
- Added comprehensive test coverage for both formats
- Updated documentation with European format examples

This improves ISO 8601 compliance and enables parsing of temporal
strings from European locales where comma is the standard decimal
separator (e.g., "T10:30:45,123" and "PT1,5S").

Author: lxcid

.changeset/european-decimal-separator.md

@@ -0,0 +1,18 @@
+---
+'@taskade/temporal-parser': patch
+---
+
+fix: Support comma as decimal separator in fractional seconds (European format)
+
+Add support for comma (`,`) as a decimal separator in fractional seconds for both time and duration components, as specified in ISO 8601. This enables parsing of European-formatted temporal strings while maintaining canonical dot (`.`) notation in serialized output.
+
+**Supported formats:**
+- Time with fractional seconds: `T10:30:45,123` → `T10:30:45.123`
+- Duration with fractional seconds: `PT1,5S` → `PT1.5S`
+
+**Behavior:**
+- Parser accepts both `.` and `,` as decimal separators
+- Stringify normalizes all output to use `.` for consistency
+- Full round-trip compatibility maintained
+
+This change improves ISO 8601 compliance and enables parsing of temporal strings from European locales where comma is the standard decimal separator.

README.md

@@ -55,6 +55,7 @@ const range = parseTemporal('2025-01-01/2025-12-31');
 - Hour-Minute: `T10:30`
 - With seconds: `T10:30:45`
 - With fractional seconds: `T10:30:45.123456789`
+- European format (comma): `T10:30:45,123` (normalized to dot in output)
 
 ### Timezones
 - UTC: `Z`
@@ -65,6 +66,7 @@ const range = parseTemporal('2025-01-01/2025-12-31');
 - Date parts: `P1Y2M3D` (1 year, 2 months, 3 days)
 - Time parts: `PT4H5M6S` (4 hours, 5 minutes, 6 seconds)
 - Combined: `P1Y2M3DT4H5M6S`
+- Fractional seconds: `PT1.5S` or `PT1,5S` (comma normalized to dot)
 
 ### IXDTF Annotations
 - Calendar: `[u-ca=gregory]`

src/parser.test.ts

@@ -72,6 +72,24 @@ describe('parseTemporal', () => {
         time: { fraction: '123456789' },
       });
     });
+
+    it('should parse fractional seconds with comma (European format)', () => {
+      const ast = parseTemporal('2025-01-07T10:30:45,123');
+      expect(ast).toMatchObject({
+        kind: 'DateTime',
+        date: { year: 2025, month: 1, day: 7 },
+        time: { hour: 10, minute: 30, second: 45, fraction: '123' },
+        annotations: [],
+      });
+    });
+
+    it('should parse fractional seconds with comma and high precision', () => {
+      const ast = parseTemporal('2025-01-07T10:30:45,123456789');
+      expect(ast).toMatchObject({
+        kind: 'DateTime',
+        time: { fraction: '123456789' },
+      });
+    });
   });
 
   describe('timezone parsing', () => {
@@ -369,6 +387,16 @@ describe('parseTemporal', () => {
       });
     });
 
+    it('should parse fractional seconds with comma (European format)', () => {
+      const ast = parseTemporal('PT1,5S');
+      expect(ast).toMatchObject({
+        kind: 'Duration',
+        seconds: 1,
+        secondsFraction: '5',
+        raw: 'PT1,5S',
+      });
+    });
+
     it('should parse combined time parts', () => {
       const ast = parseTemporal('PT2H30M45S');
       expect(ast).toMatchObject({

src/parser.ts

@@ -175,7 +175,8 @@ class Parser {
       const sTok = this.eat(TokType.Number);
       second = toInt(sTok.value, 'second', this.i);
 
-      if (this.tryEat(TokType.Dot)) {
+      // ISO 8601 allows both . and , as decimal separators for fractional seconds
+      if (this.tryEat(TokType.Dot) || this.tryEat(TokType.Comma)) {
         const fracTok = this.eat(TokType.Number);
         fraction = fracTok.value; // keep raw digits
       }
@@ -332,8 +333,10 @@ class Parser {
       rawParts.push(numTok.value);
 
       let fraction: string | undefined;
-      if (this.tryEat(TokType.Dot)) {
-        rawParts.push('.');
+      // ISO 8601 allows both . and , as decimal separators
+      const dotOrComma = this.tryEat(TokType.Dot) || this.tryEat(TokType.Comma);
+      if (dotOrComma) {
+        rawParts.push(dotOrComma.value); // Preserve the actual separator (. or ,)
         const fracTok = this.eat(TokType.Number);
         rawParts.push(fracTok.value);
         fraction = fracTok.value;

src/stringify.test.ts

@@ -526,6 +526,18 @@ describe('format normalization', () => {
     const result = stringifyTemporal(ast);
     expect(result).toBe('2025-01-12T10:00:00-08:00');
   });
+
+  it('should normalize comma decimal separator to dot', () => {
+    const ast = parseTemporal('2025-01-12T10:30:45,123');
+    const result = stringifyTemporal(ast);
+    expect(result).toBe('2025-01-12T10:30:45.123');
+  });
+
+  it('should normalize comma in duration to dot', () => {
+    const ast = parseTemporal('PT1,5S');
+    const result = stringifyTemporal(ast);
+    expect(result).toBe('PT1.5S');
+  });
 });
 
 describe('edge cases', () => {