Publish a post about reraising continuations

content/posts/reraising_continuations/note.md

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+X-Date: 2024-10-15T22:54:31Z
+X-Note-Id: e2abd2ec-c537-4e15-a4a1-7eb374d48a06
+Subject: Reraising continuations
+X-Slug: reraising_continuations
+
+Reraising errors/continuations caused me some serious head-scratching, but now it's complete.
+You can reraise errors from the guard handler, and the continuation will be reattached to
+the place where it's been taken from as if nothing has happened, and the stack unwinding will
+proceed from the current guard handler and up.
+
+An example:
+
+```
+(fn main()
+    (println "one")
+    (println "two")
+    (error "three")
+    )
+
+(guard main
+       (fn handler (err cont)
+           (if (task? err)
+               (reraise cont)
+               (println "caught error" err)
+           )))
+```
+
+Here, `main` calls 2 functions that cause side-effects and raise continuations. But the
+guard handler checks if this is a task and just reraises it, pretending that the handler
+never happened. It only will return from the handler upon receiving an error.
+
+The `reraise` building block will be very important when I start implementing a better-looking
+`try` macro. But for now it's already pretty convenient to be able to let the debug prints
+"fall through" the error handler.
+
+Check out [Valeri language](https://git.knazarov.com/knazarov/valeri) if you're interested.