Formalize grammar

.eslintignore

@@ -1,2 +1,3 @@
 dist/
 docs/
+src/sw2-ast.js

.gitignore

@@ -106,3 +106,7 @@ dist
 # Typedoc
 
 docs/
+
+# Generated grammars
+
+src/sw2-ast.js

package.json

@@ -37,6 +37,8 @@
   "scripts": {
     "lint": "gts lint",
     "clean": "gts clean",
+    "compile-parser": "peggy src/sw2.pegjs -o src/sw2-ast.js",
+    "precompile": "npm run compile-parser",
     "compile": "tsc",
     "fix": "gts fix",
     "prepare": "npm run compile",
@@ -46,6 +48,7 @@
     "doc": "typedoc --entryPointStrategy packages . --name scale-workshop-core"
   },
   "dependencies": {
+    "peggy": "^3.0.2",
     "xen-dev-utils": "^0.1.4"
   }
 }

src/__tests__/parser.spec.ts

@@ -44,6 +44,10 @@ describe('Line parser', () => {
     ).toThrow();
   });
 
+  it('rejects fractions without a numerator', () => {
+    expect(() => parseLine('/5')).toThrow();
+  });
+
   it('parses N-of-EDO (negative)', () => {
     const result = parseLine('-2\\5');
     expect(
@@ -114,6 +118,10 @@ describe('Line parser', () => {
     expect(result.type).toBe('equal temperament');
   });
 
+  it('rejects N-of-EDO without a numerator', () => {
+    expect(() => parseLine('\\8')).toThrow();
+  });
+
   it('parses monzos', () => {
     const result = parseLine('[-1, 2, 3/2, 0>');
     const components = [new Fraction(-1), new Fraction(2), new Fraction(3, 2)];
@@ -127,7 +135,8 @@ describe('Line parser', () => {
     expect(result.type).toBe('monzo');
   });
 
-  it('parses composites (positive offset)', () => {
+  // Skipped because disappearing cents have mostly caused confusion
+  it.skip('parses composites (positive offset)', () => {
     const result = parseLine('3\\5 + 5.');
     expect(result.monzo.cents).toBeCloseTo(5);
     expect(result.name).toBe('3\\5');
@@ -144,7 +153,8 @@ describe('Line parser', () => {
     expect(result.equals(expected)).toBeTruthy();
   });
 
-  it('parses composites (negative offset)', () => {
+  // See above for why this is skipped
+  it.skip('parses composites (negative offset)', () => {
     const result = parseLine('3/2 - 1.955');
     expect(result.monzo.cents).toBeCloseTo(-1.955);
     expect(result.name).toBe('3/2');

src/__tests__/sw2-ast.spec.ts

@@ -0,0 +1,96 @@
+import {describe, it, expect} from 'vitest';
+import {parse} from '../sw2-ast';
+
+describe('Scale Workshop 2 Abstract Syntax Tree Parser', () => {
+  it('parses plain numbers as plain literals ', () => {
+    const ast = parse('81');
+    expect(ast.type).toBe('PlainLiteral');
+    expect(ast.value).toBe(81);
+  });
+
+  it('parses dot-separated numbers as cents literals', () => {
+    const ast = parse('81.80');
+    expect(ast.type).toBe('CentsLiteral');
+    expect(ast.whole).toBe(81);
+    expect(ast.fractional).toBe('80');
+  });
+
+  it('parses comma-separated numbers as numeric literals', () => {
+    const ast = parse('81,80');
+    expect(ast.type).toBe('NumericLiteral');
+    expect(ast.whole).toBe(81);
+    expect(ast.fractional).toBe('80');
+  });
+
+  it('parses leading zeroes in the fractional part of cents literals', () => {
+    const ast = parse('.00123');
+    expect(ast.type).toBe('CentsLiteral');
+    expect(ast.whole).toBe(null);
+    expect(ast.fractional).toBe('00123');
+  });
+
+  it('parses leading zeroes in the fractional part of numeric literals', () => {
+    const ast = parse(',00123');
+    expect(ast.type).toBe('NumericLiteral');
+    expect(ast.whole).toBe(null);
+    expect(ast.fractional).toBe('00123');
+  });
+
+  it('parses slash-separated numbers as fraction literals', () => {
+    const ast = parse('81/80');
+    expect(ast.type).toBe('FractionLiteral');
+    expect(ast.numerator).toBe(81);
+    expect(ast.denominator).toBe(80);
+  });
+
+  it('parses backslash-separated numbers as EDJI fractions', () => {
+    const ast = parse('5\\7');
+    expect(ast.type).toBe('EdjiFraction');
+    expect(ast.numerator).toBe(5);
+    expect(ast.denominator).toBe(7);
+    expect(ast.equave).toBe(null);
+  });
+
+  it('parses EDJI fractions with explicit equaves', () => {
+    const ast = parse('6\\13<3>');
+    expect(ast.type).toBe('EdjiFraction');
+    expect(ast.numerator).toBe(6);
+    expect(ast.denominator).toBe(13);
+    expect(ast.equave.type).toBe('PlainLiteral');
+    expect(ast.equave.value).toBe(3);
+  });
+
+  it('parses space-separated numbers between a square and an angle bracket as monzos', () => {
+    const ast = parse('[-4 4 -1>');
+    expect(ast.type).toBe('Monzo');
+    expect(ast.components).toEqual(['-4', '4', '-1']);
+  });
+
+  it('parses comma-separated numbers between a square and an angle bracket as monzos', () => {
+    const ast = parse('[-4, 4, -1>');
+    expect(ast.type).toBe('Monzo');
+    expect(ast.components).toEqual(['-4', '4', '-1']);
+  });
+
+  it('parses unary negated EDJI', () => {
+    const ast = parse('-1\\12');
+    expect(ast.type).toBe('UnaryExpression');
+    expect(ast.operator).toBe('-');
+    expect(ast.operand.type).toBe('EdjiFraction');
+    expect(ast.operand.numerator).toBe(1);
+    expect(ast.operand.denominator).toBe(12);
+    expect(ast.operand.equave).toBe(null);
+  });
+
+  it('parses binary added numbers and cents', () => {
+    const ast = parse('2 + 1.23');
+    expect(ast.type).toBe('BinaryExpression');
+    expect(ast.operator).toBe('+');
+  });
+
+  it('parses binary subtracted numbers and cents', () => {
+    const ast = parse('2 - 1.23');
+    expect(ast.type).toBe('BinaryExpression');
+    expect(ast.operator).toBe('-');
+  });
+});

src/monzo.ts

@@ -145,6 +145,9 @@ export class ExtendedMonzo {
     while (vector.length < numberOfComponents) {
       vector.push(new Fraction(0));
     }
+    if (value === 0) {
+      return new ExtendedMonzo(vector, new Fraction(0), 0);
+    }
     return new ExtendedMonzo(vector, undefined, valueToCents(value));
   }