Display Haskell exceptions in browser

[srid]

When rendering a route if the user code throws an exception, display the stacktrace in the browser.

A simple try ... catch around the render function here, with the handler returning the traceback HTML, should do the job:

ema/src/Ema/Server.hs

Lines 64 to 66 in 15eeeb8

	routeHtml :: model -> route -> LByteString
	routeHtml m r = do
	render m r <> emaStatusHtml <> wsClientShim

[srid]

Without handling exceptions the client websocket fails with Invalid frame header error, and this is shown on the server, repeatedly:

Here, "Unknown measure: TAGS" is the exception being thrown.

[srid]

Resolution coming, with a trivial UI. It can be latter be enriched