Store full MOS config for reconstruction

src/context.ts

@@ -2,8 +2,7 @@ import {SonicWeaveValue} from './stdlib';
 import {Interval} from './interval';
 import {TimeMonzo} from './monzo';
 import {ZERO} from './utils';
-import {MosConfig, scaleMonzos} from './diamond-mos';
-import {stepString} from './words';
+import {MosConfig} from './diamond-mos';
 
 /**
  * Root context of a SonicWeave runtime containing the scale title, root pitch, value of the 'up' inflection etc.
@@ -168,18 +167,9 @@ export class RootContext {
       lines.push(`/ = ${this.lift.toString()}`);
     }
     if (this.mosConfig) {
-      const monzos = scaleMonzos(this.mosConfig);
-      const ss = stepString(monzos);
-      let large: TimeMonzo;
-      let small: TimeMonzo;
-      if (ss.startsWith('L')) {
-        large = monzos[0];
-        small = large.div(this.mosConfig.am) as TimeMonzo;
-      } else {
-        small = monzos[0];
-        large = small.mul(this.mosConfig.am) as TimeMonzo;
-      }
-      lines.push(`MOS {${ss};L=${large};s=${small}}`);
+      lines.push(
+        `MOS {${this.mosConfig.pattern};L=${this.mosConfig.large};s=${this.mosConfig.small}}`
+      );
     }
     return lines.join('\n');
   }

src/diamond-mos.ts

@@ -58,6 +58,18 @@ export type MosConfig = {
    * Intervals for relative notation. Use period to reach larger intervals.
    */
   degrees: MosDegree[];
+  /**
+   * Pattern for reconstructing the MOS declaration.
+   */
+  pattern: string;
+  /**
+   * Value of the large step.
+   */
+  large: TimeMonzo;
+  /**
+   * Value of the small step.
+   */
+  small: TimeMonzo;
 };
 
 /**

src/parser/__tests__/source.spec.ts

@@ -1652,4 +1652,72 @@ describe('SonicWeave parser', () => {
       145.94801056814464, 165.55065597696213, 176.31825099920434, 200,
     ]);
   });
+
+  it('allows you to call the smaller step L in MOS declaration', () => {
+    const scale = expand(`
+      MOS {
+        3L 2s
+        L = 9/8
+      }
+      automos()
+      relative
+      linear
+    `);
+    expect(scale).toEqual([
+      'MOS {LLsLs;L=9/8;s=32/27}',
+      '9/8',
+      '81/64',
+      '3/2',
+      '27/16',
+      '2',
+    ]);
+  });
+
+  it('allows you to create negative steps', () => {
+    const scale = expand(`
+      MOS {
+        6L 1s
+        L = 9/8
+      }
+      automos()
+      relative
+      linear
+    `);
+    expect(scale).toEqual([
+      'MOS {LLLLLLs;L=9/8;s=524288/531441}',
+      '9/8',
+      '81/64',
+      '729/512',
+      '6561/4096',
+      '59049/32768',
+      '531441/262144',
+      '2',
+    ]);
+  });
+
+  it('preserves equalized MOS declaration', () => {
+    const scale = expand(`
+      MOS {
+        5L 2s
+        L = 1\\7
+      }
+      M1ms
+      M2ms
+      P3ms
+      P4ms
+      M5ms
+      M6ms
+      P7ms
+    `);
+    expect(scale).toEqual([
+      'MOS {LLLsLLs;L=2^1/7;s=2^1/7}',
+      'M1ms',
+      'M2ms',
+      'P3ms',
+      'P4ms',
+      'M5ms',
+      'M6ms',
+      'P7ms',
+    ]);
+  });
 });

src/parser/mos.ts

@@ -148,6 +148,9 @@ export class Tardigrade {
       period: r(notation.period),
       scale,
       degrees,
+      pattern: this.pattern,
+      large,
+      small,
     };
   }