The Rel Forum

The <substitute> operator does not always parse correctly.

Example:
UPDATE S (STATUS := 17)

The opening parenthesis is interpreted as being part of the expression to perform substitution on rather than the beginning of the assignment. It is taken as denoting the opening parenthesis for a user-defined operator invocation, until it reaches the := token and then it gives up and incorrectly reports a syntax error.

Adrian

Yup, this is a known bug documented at http://dbappbuilder.sourceforge.net/Rel.php in the "Limitations" section. Thanks for reminding me of it, though; I meant to tackle it long ago, but forgot!