Remove lest assignment due to no change possible

Add a note about lest associativity.
xenharmonic-devs · Apr 30, 2024 · 051ac69 · 051ac69
1 parent 565684c
commit 051ac69
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diff --git a/documentation/technical.md b/documentation/technical.md
@@ -51,10 +51,12 @@ All operations are left-associative except exponentiation, recipropower, and log
 | `and`, `vand`                                    | Boolean and, vector and                                                 |
 | `or`, `vor`, `??`                                | Boolean or, vector or, niente coalescing                                |
 | `x if y else z`                                  | Ternary conditional                                                     |
-| `lest`                                           | Fallback                                                                |
+| `lest`                                           | Fallback[^1]                                                                |
 
 Parenthesis, `^`, `×`, `÷`, `+`, `-` follow [PEMDAS](https://en.wikipedia.org/wiki/Order_of_operations). The fraction slash `/` represents vertically aligned fractions similar to `$\frac{3}{2}^\frac{1}{2}$` in LaTeX e.g. `3/2 ^ 1/2` evaluates to `sqrt(3 ÷ 2)`.
 
+[^1]: `lest` is a fully associative operation, thus `a() lest b() lest c()` = `(a() lest b()) lest c()` = `a() lest (b() lest c())`. This means that one can always treat a sequence `a() lest b() lest ... lest c()` as if the evaluations occurred from left to right. Any possible parenthesis may be ignored in such a sequence.
+
 ## Interval subtypes
 
 TODO: List all interval subtypes

diff --git a/src/grammars/sonic-weave.pegjs b/src/grammars/sonic-weave.pegjs
@@ -552,8 +552,7 @@ Expression
   = LestExpression
 
 AssigningOperator
-  = LestOperator
-  / CoalescingOperator
+  = CoalescingOperator
   / ConjunctOperator
   / RoundingOperator
   / ExtremumOperator

diff --git a/src/parser/__tests__/expression.spec.ts b/src/parser/__tests__/expression.spec.ts
@@ -1472,20 +1472,31 @@ describe('SonicWeave expression evaluator', () => {
     expect(pi.valueOf()).toBeCloseTo(Math.PI);
   });
 
-  it('has an inline analogue of try..catch (right failure)', () => {
-    const pi = evaluate('fraction(E) lest fraction(PI) lest PI') as Interval;
-    expect(pi.value.isFractional()).toBe(false);
-    expect(pi.valueOf()).toBeCloseTo(Math.PI);
+  it('has an inline analogue of try..catch (ternary fail.fail.fail)', () => {
+    expect(() =>
+      evaluate('fraction(E) lest fraction(PI) lest fraction(LN2)')
+    ).toThrow('Input is irrational and no tolerance given.');
   });
 
-  it('has inline analogue of assignment inside try..catch', () => {
-    const pi = evaluate(
-      'let halfTau = PI;halfTau lest= fraction(halfTau);halfTau'
-    ) as Interval;
-    expect(pi.value.isFractional()).toBe(false);
-    expect(pi.value.isFractional()).toBe(false);
-    expect(pi.valueOf()).toBeCloseTo(Math.PI);
-    expect(pi.valueOf()).toBeCloseTo(Math.PI);
+  it('has an inline analogue of try..catch (ternary fail.fail.success)', () => {
+    const {fraction} = parseSingle(
+      'fraction(E) lest fraction(PI) lest fraction(LN2, 10.)'
+    );
+    expect(fraction).toBe('9/13');
+  });
+
+  it('has an inline analogue of try..catch (ternary fail.success.no-eval)', () => {
+    const {fraction} = parseSingle(
+      'fraction(E) lest fraction(PI, 10.) lest fraction(LN2)'
+    );
+    expect(fraction).toBe('22/7');
+  });
+
+  it('has an inline analogue of try..catch (ternary success.no-eval.no-eval)', () => {
+    const {fraction} = parseSingle(
+      'fraction(E, 10.) lest fraction(PI, 10.) lest fraction(LN2)'
+    );
+    expect(fraction).toBe('19/7');
   });
 
   it('has atan2 with swapped arguments', () => {