Force-configuration-time Expression

CastExpr := '#' CastExpr

This is a bridging production from the nonterminal CastExpr in C, which is to match expressions with precedence equal or higher than type-casts. Here, it is used to force an expression inside a lambda expression construct to be evaluated at configuration time, i.e. when the lambda expression is constructed as opposed to when it is executed (related to the lambda configuration feature), also it makes the bound to be by-value instead of the default mode of by-reference. More concretely, this feature is used in setting configure parameters in generator configuration construction, and in some array helpers in the body of rule definitions.