Awesome! I've googled high and low for exactly this functionality in
the past. +1 for getting this into core or contrib if it could work
there. Can you wrap a require to make a whole library debuggable?
(with-lexical-frames (require 'foo.bar))
It would be very handy to have a debug mode where exceptions
automatically drop you into a repl with all of the associated
environment for you to explore. I guess something ala Smalltalk
systems...
-Jeff
On Dec 7, 9:37 pm, George Jahad <cloj...@blackbirdsystems.net> wrote:
> Every time I stick a println into some Clojure code to debug it, I
> think to myself, "This is Lisp! I should be able to insert a repl
> here!"
>
> The problem is of course that Clojure's eval function doesn't know
> about the surrounding lexical scope. So I started asking myself, what
> is the simplest change I could make to Clojure to support an eval that
> understands that scope? Then I tried to implement it.
>
> Basically, here's what I came up with.
>
> 1. Modify the Clojure compiler so that when a flag is turned on, it
> stores references to the lexical scope in a dynamic var. Thus, each
> time the compiler creates a new lexical scope, it also emits the byte
> code to push a hash-map with the details onto the var. When that scope
> ends, the byte code for popping the hash-map off the var is emitted.
>
> 2. Then in Clojure proper, add a special version of eval that uses
> that var. It wraps the form being eval'ed in a "let" that emulates the
> original lexical scope, something like this:
>
> `(eval
> (let [~@(make-let-bindings
> (:lexical-frames (var-get (resolve context))))]
> ~form))
>
> With those two pieces, it's straight-forward creating a "debug-repl"
> that understands the surrounding lexical scope.
>
> I'm pretty pleased with the results and wanted to show them off. More
> details here:http://georgejahad.com/clojure/debug-repl.html
>
> Thanks to the my coworkers, the "Sonian-Clojure Brain Trust", for
> their support and encouragement!
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