branch beam-0500: Updates with the field referenced at the right hand side of the assignment

[gibranrosa]

With the code below:
runUpdate $ update ordersT (\order -> [_orderAmount order <-. (_orderAmount order *100)]) (\order -> _orderTakenBy order ==. (pk tomJones))

It shows the error:
Error: * Couldn't match type QField s Scientific' with QGenExpr QValueContext FirebirdExpressionSyntax s Scientific'
Expected type: QExpr FirebirdExpressionSyntax s Scientific
Actual type: Columnar (QField s) Scientific

• In the first argument of (*)', namely _orderAmount order'
  In the second argument of (<-.)', namely (_orderAmount order * 100)'
  In the expression:
  _orderAmount order <-. (_orderAmount order * 100)
• Relevant bindings include
  order :: OrderT (QField s) (bound at example\EmployeesFB.hs:211:19)

[tathougies]

The problem here is that order in the second argument to update is parameterized over QField, which is conceptually the type of expressions on the 'left-hand side' of the UPDATE ... SET ... assignments. However, you want to use it as both a QField and QExpr -- this is a case I hadn't thought of, but ought to be supported.

We could pass in two tables to the second argument of update (one QField and one QExpr), but then the syntax becomes awkward and obtuse.

Any ideas on a better solution / syntax?

[gibranrosa]

It worked! Thanks!