fix: lenient parse "foo"

Author: arnog

src/compute-engine/latex-syntax/parse.ts

@@ -1552,6 +1552,11 @@ export class _Parser implements Parser {
 
     const start = this.index;
 
+    // Word boundary: if the preceding token is a letter, we're in the
+    // middle of a word that was partially consumed — don't match.
+    if (start > 0 && /^[a-zA-Z]$/.test(this._tokens[start - 1]))
+      return null;
+
     // Collect consecutive letter tokens to form a potential function name
     let name = '';
     while (!this.atEnd && /^[a-zA-Z]$/.test(this.peek)) {
@@ -1711,6 +1716,11 @@ export class _Parser implements Parser {
 
     const start = this.index;
 
+    // Word boundary: if the preceding token is a letter, we're in the
+    // middle of a word that was partially consumed — don't match.
+    if (start > 0 && /^[a-zA-Z]$/.test(this._tokens[start - 1]))
+      return null;
+
     // Collect consecutive letter tokens
     let name = '';
     while (!this.atEnd && /^[a-zA-Z]$/.test(this.peek)) {

test/compute-engine/latex-syntax/parsing.test.ts

@@ -215,9 +215,9 @@ describe('NON-STRICT MODE (Math-ASCII/Typst-like syntax)', () => {
     });
 
     test('Unknown function names are rejected', () => {
-      // 'foo' is not a recognized function: 'f' is a symbol, 'oo' is infinity
+      // 'foo' is not a recognized function, should parse as individual symbols
       expect(ce.parse('foo(x)', { strict: false })).toMatchInlineSnapshot(
-        `["Triple", "f", "PositiveInfinity", "x"]`
+        `["Tuple", "f", "o", "o", "x"]`
       );
     });
   });