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Compiler bug?
f#compiler

Can anyone explain to me why this compiles (and does what it is supposed to do):

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            member this.GetTemplate template = 
                
                let ctx = ref (this)
                let setterWrapper manager =
                    ctx := new Context(manager, externalContext, variables, managerSetter)
                    managerSetter(manager)
                let a = setterWrapper
                !ctx :> IContext, (manager :?> Manager).GetTemplate template setterWrapper

and this one gives a compiler error "The value or constructor 'setterWrapper' is not defined."

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            member this.GetTemplate template = 
                
                let ctx = ref (this)
                let setterWrapper manager =
                    ctx := new Context(manager, externalContext, variables, managerSetter)
                    managerSetter(manager)
                //let a = setterWrapper
                !ctx :> IContext, (manager :?> Manager).GetTemplate template setterWrapper
.

The precedence of the upcast operators :> and :?> in the language grammar is rather unexpected; the fix is to put parens around the upcast expression:

(!ctx :> IContext), ...

By on 7/6/2009 9:15 PM ()

Thanks for the response. Adding the parens did fix it.

I am still lost though as to how in the world missing parens can cause the compiler to loose the binding? In other words the next time I see the message how am I to guess that the problem is in the parens?

By on 7/7/2009 5:12 PM ()

I think that it must be parsing it in a way such that it swallows the previous 'let', e.g.

let a = blah

let b = blah

foo :> Type, b

parses as

let a = blah

(let b = blah

foo :> Type), b

but I haven't studied the language grammar carefully to verify it.

I would recommend always surrounding upcast expressions with parens.

By on 7/7/2009 5:50 PM ()

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