Handle errors in readExpr

src/runtime/javascript/index.ts

@@ -201,6 +201,9 @@ function newNGF (abstract_name: string, path?: string): PGFGrammar {
 function readExpr (str: string): Expr {
   const txt = PgfText_FromString(str)
   const expr = runtime.pgf_read_expr(txt, unmarshaller.ref())
+  if (ref.isNull(expr)) {
+    throw new PGFError('unable to parse expression')
+  }
   return ref.readObject(expr) as Expr
 }
 

src/runtime/javascript/tests/basic.test.ts

@@ -210,6 +210,13 @@ describe('abstract syntax', () => {
 // ----------------------------------------------------------------------------
 
 describe('expressions', () => {
+  test('invalid', () => {
+    expect(() => {
+      PGF.readExpr('->')
+    }).toThrow(PGF.PGFError)
+  })
+
+  describe('literals', () => {
     test('small integer', () => {
       const e1 = PGF.readExpr('123')
       const e2 = new PGF.ExprLit(123)
@@ -286,3 +293,4 @@ describe('expressions', () => {
       expect(e1).not.toEqual(e3)
     })
   })
+})