Parse N-of-EDO with missing numerators

ref xenharmonic-devs/scale-workshop#537

src/__tests__/parser.spec.ts

@@ -151,8 +151,21 @@ describe('Line parser', () => {
     expect(result.type).toBe('equal temperament');
   });
 
-  it('rejects N-of-EDO without a numerator', () => {
-    expect(() => parseLine('\\8')).toThrow();
+  it('accepts N-of-EDO without a numerator', () => {
+    const result = parseLine('\\8');
+    expect(
+      result.equals(
+        new Interval(
+          ExtendedMonzo.fromEqualTemperament(
+            0,
+            2,
+            DEFAULT_NUMBER_OF_COMPONENTS
+          ),
+          'equal temperament'
+        )
+      )
+    ).toBeTruthy();
+    expect(result.type).toBe('equal temperament');
   });
 
   it('parses monzos', () => {

src/parser.ts

@@ -45,7 +45,7 @@ type FractionLiteral = {
 
 type EdjiFraction = {
   type: 'EdjiFraction';
-  numerator: number;
+  numerator?: number;
   denominator: number;
   equave: null | PlainLiteral | FractionLiteral;
 };
@@ -199,7 +199,7 @@ function evaluateAst(
       );
   }
   if (ast.type === 'EdjiFraction') {
-    const fractionOfEquave = new Fraction(ast.numerator, ast.denominator);
+    const fractionOfEquave = new Fraction(ast.numerator ?? 0, ast.denominator);
     let equave: Fraction | undefined;
     if (ast.equave?.type === 'PlainLiteral') {
       equave = new Fraction(ast.equave.value);

src/sw2.pegjs

@@ -132,7 +132,7 @@ EquaveExpression
   = '<' _ @(SlashFraction / PlainNumber) _ '>'
 
 BackslashFraction
-  = numerator:Integer '\\' denominator:SignedInteger equave:EquaveExpression? { return EdjiFraction(numerator, denominator, equave) }
+  = numerator:Integer? '\\' denominator:SignedInteger equave:EquaveExpression? { return EdjiFraction(numerator, denominator, equave) }
 
 Component
   = $([+-]? (SlashFraction / PlainNumber))