fix(HF-268): support consecutive percent operators

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ### Fixed
 
+- Fixed parsing of consecutive percent operators, such as `=5%%`. [#1773](https://github.com/handsontable/hyperformula/pull/1773)
 - Fixed the `AVERAGEIF` function returning a division-by-zero error when the calculated average was `0`. [#1733](https://github.com/handsontable/hyperformula/pull/1733)
 - Fixed the localized names of `VSTACK` and `HSTACK` in 14 language packs to match Microsoft Excel. [#1748](https://github.com/handsontable/hyperformula/pull/1748)
 - Fixed the MAXPOOL and MEDIANPOOL functions throwing an uncaught `TypeError` instead of returning the `#VALUE!` error when the range dimensions are not a whole multiple of the window size and the stride. [#1718](https://github.com/handsontable/hyperformula/pull/1718)

docs/guide/types-of-operators.md

@@ -38,7 +38,11 @@ returns the negative value of that number.
 | :--- | :--- | :--- | :--- |
 | - | Unary minus | -a | Returns the negative of its argument. |
 | + | Unary plus | +a | Returns the positive of its argument. |
-| % | Percent | a% | Calculate the percent of an argument. |
+| % | Percent | a% | Divides its argument by 100. |
+
+HyperFormula supports consecutive percent operators. Each `%` divides the
+preceding result by `100`. For example, `=5%%` is equivalent to `=(5%)%`
+and returns `0.0005`, while `=5%%%` returns `0.000005`.
 
 ## Binary arithmetic operators
 

src/parser/FormulaParser.ts

@@ -561,18 +561,18 @@ export class FormulaParser extends EmbeddedActionsParser {
     ])) as Ast
   })
 
+  /**
+   * Rule for atomic expressions followed by zero or more percent operators.
+   */
   private rightUnaryOpAtomicExpression: AstRule = this.RULE('rightUnaryOpAtomicExpression', () => {
-    const positiveAtomicExpression = this.SUBRULE(this.positiveAtomicExpression)
-
-    const percentage = this.OPTION(() => {
-      return this.CONSUME(PercentOp)
-    }) as Maybe<ExtendedToken>
+    let expression: Ast = this.SUBRULE(this.positiveAtomicExpression)
 
-    if (percentage) {
-      return buildPercentOpAst(positiveAtomicExpression, percentage.leadingWhitespace)
-    }
+    this.MANY(() => {
+      const percentage = this.CONSUME(PercentOp) as ExtendedToken
+      expression = buildPercentOpAst(expression, percentage.leadingWhitespace)
+    })
 
-    return positiveAtomicExpression
+    return expression
   })
 
   /**