Re: [web-devel] Hamlet variable interpolation syntax [previously: A few questions about Yesod]

On Fri, Dec 31, 2010 at 3:45 AM, Mark Bradley wrote:

On Fri, Dec 31, 2010 at 11:58 AM, Felipe Almeida Lessa wrote:

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On Thu, Dec 30, 2010 at 6:45 PM, Michael Snoyman wrote:

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I'm beginning to lean that direction as well. As far as forall/maybe syntax, I propose adding a comma:

$forall foo bar baz, bin

What about something like

$forall bin <- foo bar baz

I like this syntax, but the comma also works for me.

I too could go either way, and neither is particularly complicated to implement. A separate question, since it's bugged me for a bit now: there's a minor inconsistency, since maybe is paired with nothing. In theory, it should be just/nothing. However, it still "feels" like maybe is a better choice, though this could just be because I got used to it. Any other thoughts?

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We could even support pattern matches, which would be very useful on some cases:

$forall Person name age address <- people

I know, I know, bad example, it's just to get the idea across. =)

I know it is possible, but the difficulty of bringing in more haskell features into hamlet is that hamlet's interpreter is written from scratch.  So unless someone gets an itch to grab a chunk of ghcs source code so we can run it at compile time in a template haskell context.  There has to be a better way than reinventing that wheel.

I concur on this one. The one place where I've really considered using pattern match syntax is for tuples, which maybe *should* be implemented now. With proper datatypes, the record accessors are usually very clear. Michael