fix #130

Author: arnog

CHANGELOG.md

@@ -2,6 +2,16 @@
 
 ### Bug Fixes
 
+- **([#130](https://github.com/cortex-js/compute-engine/issues/130)) Prefix/Postfix
+  Operator LaTeX Serialization**: Fixed incorrect LaTeX output for prefix operators
+  (like `Negate`) and postfix operators (like `Factorial`) when applied to
+  expressions with lower precedence. Previously, `Negate(Add(a, b))` incorrectly
+  serialized as `-a+b` instead of `-(a+b)`, causing round-trip failures where
+  parsing the output produced a mathematically different expression. Similarly,
+  `Factorial(Add(a, b))` now correctly serializes as `(a+b)!` instead of `a+b!`.
+  The fix ensures operands are wrapped in parentheses when their precedence is
+  lower than the operator's precedence.
+
 - **Rules Cache Isolation**: Fixed rules cache building failing with "Invalid
   rule" errors when user expressions had previously polluted the global scope.
   For example, parsing `x(y+z)` would add `x` as a symbol with function type to

src/compute-engine/latex-syntax/dictionary/definitions.ts

@@ -486,13 +486,15 @@ function makeSerializeHandler(
   // We have a LaTeX version of the symbol
   //
   if (latex) {
+    const prec = entry['precedence'] ?? 10000;
+
     if (kind === 'postfix')
       return (serializer, expr) =>
-        joinLatex([serializer.serialize(operand(expr, 1)), latex!]);
+        joinLatex([serializer.wrap(operand(expr, 1), prec), latex!]);
 
     if (kind === 'prefix')
       return (serializer, expr) =>
-        joinLatex([latex!, serializer.serialize(operand(expr, 1))]);
+        joinLatex([latex!, serializer.wrap(operand(expr, 1), prec)]);
 
     if (kind === 'infix') {
       return (serializer, expr) => {
@@ -523,26 +525,28 @@ function makeSerializeHandler(
   // We do not have a LaTeX version of the symbol. Use a string symbol
   //
   const id = idTrigger ?? entry.name ?? 'unknown';
+  const prec = entry['precedence'] ?? 10000;
+
   if (kind === 'postfix')
     return (serializer, expr) =>
       joinLatex([
-        serializer.serialize(operand(expr, 1)),
+        serializer.wrap(operand(expr, 1), prec),
         serializer.serializeSymbol(id),
       ]);
 
   if (kind === 'prefix')
     return (serializer, expr) =>
       joinLatex([
         serializer.serializeSymbol(id),
-        serializer.serialize(operand(expr, 1)),
+        serializer.wrap(operand(expr, 1), prec),
       ]);
 
   if (kind === 'infix')
     return (serializer, expr) =>
       joinLatex([
-        serializer.serialize(operand(expr, 1)),
+        serializer.wrap(operand(expr, 1), prec + 1),
         serializer.serializeSymbol(id),
-        serializer.serialize(operand(expr, 2)),
+        serializer.wrap(operand(expr, 2), prec + 1),
       ]);
 
   // Function, symbol or expression. Depends on the actual shape of the