[web-devel] style for html IDs in hamlet

[Michael Snoyman]

On Fri, Apr 8, 2011 at 5:03 PM, Max Cantor <mxcantor at gmail.com> wrote:

> In an effort to get more type-checked goodness in hamlet, I started using
> string constants for all my dom IDs and classes.  We're not using the
> newIdent function because I want control over what the IDs and classes will
> be named.
>
> I wrote up a little typeclass as such:
>
> class CustomIdentString a where jqVal :: a -> String; idVal :: a -> String
>
> newtype CustomIdentCls = MkCls String
> instance CustomIdentString CustomIdentCls where
>  jqVal (MkCls s) = "." ++ s; idVal (MkCls s) = s;
>
> newtype CustomIdentId = MkId String
> instance CustomIdentString CustomIdentId where
>  jqVal (MkId s) = "#" ++ s; idVal (MkId s) = s;
>
> This way, I can refer to divs in javascript using:
> $("#{jqVal myId}").foo..
>
> And create the elements in hamlet using
> <div ##{idVal myId}> ...
>
> I'm wondering is there a datatype for IDs and Classes that I can use to
> make the IDs and Classes directly so that:
> <div .#{foo myId}> and <div ##{foo myCls}>
> would fail to typecheck?
>
> In general, are there any good, safe ways to do this instead of just
> unwrapping to strings?
>
>
It's entirely possible to provide separate datatypes for IDs and classes at
the Hamlet level. The problem is, you will either always need to use them in
place of String/Text, or we'll need to have a separate typeclass for each
and triple the number of instance declarations. My opinion: it's a good idea
in theory, but will be more trouble than it's worth in practice.

One recommendation for your existing code: instead of calling jqVal and
idVal directly, declare instances of ToHtml and ToJavascript.

Michael
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