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Quotations - Equality active pattern and constructs relative to imperative prog.
f#parsingweb

Hi all,

I don't get exactly the purpose of the Raw.Equality active pattern. Why is it needed?

eg.

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[<ReflectedDefinition>]
let foo x =
  let y = if(x = 0.2f) then 0 else 1
  y

It appears that when parsing the AST of this expr, you'll find for the c expr of Raw.Cond(c, a, b) an Equality active pattern inside that compares a Raw.Bool (wich has the true value in this case) with the Raw.GenericTopDefnApp <@@ ( = ) @@> (ty, a::b::[]) recognizing the "x = 0.2f" expr

It ends up looking like a bit to if( true = (x = 0.2f)) then 0 else 1 wich contain redundancy.

Secondly I don't get the full picture on how tomasp did the job of writing web applications in F# since some constructs related to imperative programming (mutable, assignments to locals) may not be quoted. Maybe you just have to forget them for the moment ?

Many thanks

Russell Bell

.

Hi,
I'm not sure about the Raw.Equality pattern, but regarding your second question about constructs not supported by quotations - You're right that some of them aren't supported, but there are not so many of them (aside from mutable locals, there are also exceptions, but that should be probably all from the core langauge). Hopefuly, this will change in the future :-).

In F# WebTools, exceptions are currently handled quite poorly (it could be emulated using "primitive" functions that the translator would understand: catch (fun () -> ... ) (fun ex -> ...)). Mutable locals have to be written using "ref" type, which can be quoted without any troubles:

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<@ let a = ref 0 in a := 1; a @>;;

T.

By on 8/25/2008 5:34 AM ()

Thanks Tomáลก!

Apparently the Raw.Equality active pattern is now gone in the CTP... So we will never know, exactly just like what the Grand Gallery inside the Great Pyramid was for [:)]

stringer

By on 9/3/2008 3:08 PM ()

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