From 2dce6f8c43f9e0115db8838c1544eeae00790b5f Mon Sep 17 00:00:00 2001
From: Lumi Pakkanen <lumi.pakkanen@gmail.com>
Date: Mon, 13 May 2024 19:42:27 +0300
Subject: [PATCH] Admit inf in the universal monzo basis

---
 src/__tests__/cli.spec.ts               | 6 +++---
 src/expression.ts                       | 2 +-
 src/grammars/base.pegjs                 | 2 +-
 src/monzo.ts                            | 7 ++++++-
 src/parser/__tests__/expression.spec.ts | 6 ++++++
 src/warts.ts                            | 3 +++
 6 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/__tests__/cli.spec.ts b/src/__tests__/cli.spec.ts
index cb211ef8..93fd0569 100644
--- a/src/__tests__/cli.spec.ts
+++ b/src/__tests__/cli.spec.ts
@@ -17,9 +17,9 @@ describe('Interchange format', () => {
     expect(result).toContain('nan');
   });
 
-  it('has representation for infinity Hz', () => {
-    const result = toSonicWeaveInterchange('inf * 1 Hz');
-    expect(result).toContain('inf * 1Hz');
+  it('has representation for negative infinity Hz', () => {
+    const result = toSonicWeaveInterchange('-inf * 1 Hz');
+    expect(result).toContain('[1. 1 1>@Hz.-1.inf');
   });
 
   it('has representation for nan Hz (normalizes)', () => {
diff --git a/src/expression.ts b/src/expression.ts
index 02d90c9d..1ab228b5 100644
--- a/src/expression.ts
+++ b/src/expression.ts
@@ -74,7 +74,7 @@ export type WartBasisElement = BasisFraction | '';
 
 export type ValBasisElement = WartBasisElement | 's' | 'Hz' | 'hz';
 
-export type BasisElement = ValBasisElement | 'rc' | 'r¢' | '1°';
+export type BasisElement = ValBasisElement | 'rc' | 'r¢' | 'inf' | '1°';
 
 export type IntegerLiteral = {
   type: 'IntegerLiteral';
diff --git a/src/grammars/base.pegjs b/src/grammars/base.pegjs
index 57ab9cca..1f6c7b29 100644
--- a/src/grammars/base.pegjs
+++ b/src/grammars/base.pegjs
@@ -246,7 +246,7 @@ SecondToken   = @'s'  !IdentifierPart
 
 ValBasisElement = Fraction / SecondToken / HertzToken / LowHertzToken
 
-BasisElement = ValBasisElement / RealCentToken / 'r¢' / '1°' / ''
+BasisElement = ValBasisElement / RealCentToken / 'r¢' / 'inf' / '1°' / ''
 
 ValBasis = (ValBasisElement / '')|.., '.'|
 
diff --git a/src/monzo.ts b/src/monzo.ts
index d9154aa7..2736ce9c 100644
--- a/src/monzo.ts
+++ b/src/monzo.ts
@@ -746,7 +746,7 @@ export class TimeReal {
    * @returns Monzo literal.
    */
   asMonzoLiteral(interchange = false): MonzoLiteral | undefined {
-    if (!isFinite(this.value)) {
+    if (isNaN(this.value)) {
       return undefined;
     }
     const components: VectorComponent[] = [];
@@ -801,6 +801,11 @@ export class TimeReal {
       });
       return {type: 'MonzoLiteral', components, ups: 0, lifts: 0, basis};
     }
+    if (!isFinite(this.value)) {
+      basis.push('inf');
+      components.push({sign: '', left: 1, right: '', exponent: null});
+      return {type: 'MonzoLiteral', components, ups: 0, lifts: 0, basis};
+    }
     basis.push('rc');
     const {sign, whole, fractional, exponent} = numberToDecimalLiteral(
       this.totalCents(true),
diff --git a/src/parser/__tests__/expression.spec.ts b/src/parser/__tests__/expression.spec.ts
index 9ccc65b5..797490c7 100644
--- a/src/parser/__tests__/expression.spec.ts
+++ b/src/parser/__tests__/expression.spec.ts
@@ -2397,4 +2397,10 @@ describe('Poor grammar / Fun with "<"', () => {
     expect(interval.isAbsolute()).toBe(false);
     expect(interval.valueOf()).toBeCloseTo(Math.PI);
   });
+
+  it('parses universal negative infinite frequency', () => {
+    const interval = evaluate('[1. 1 1>@Hz.-1.inf') as Interval;
+    expect(interval.isAbsolute()).toBe(true);
+    expect(interval.valueOf()).toBe(-Infinity);
+  });
 });
diff --git a/src/warts.ts b/src/warts.ts
index 9b5037f2..14c7f10c 100644
--- a/src/warts.ts
+++ b/src/warts.ts
@@ -12,6 +12,7 @@ const TWO_MONZO = new TimeMonzo(ZERO, [ONE]);
 const SECOND_MONZO = new TimeMonzo(ONE, []);
 const HERTZ_MONZO = new TimeMonzo(NEGATIVE_ONE, []);
 const REAL_CENT_MONZO = new TimeReal(0, 1.0005777895065548);
+const INF_MONZO = new TimeReal(0, Infinity);
 
 export const STEP_ELEMENT = Symbol();
 
@@ -57,6 +58,8 @@ export function parseSubgroup(basis: BasisElement[], targetSize?: number) {
     } else if (element === 'rc' || element === 'r¢') {
       subgroup.push(REAL_CENT_MONZO);
       checkSpan();
+    } else if (element === 'inf') {
+      subgroup.push(INF_MONZO);
     } else if (element === '1°') {
       subgroup.push(STEP_ELEMENT);
       checkSpan();