Sequence and Eduction produce infinite loop in transducer that appends to the reduction

Description

Example: a transducer that appends :foo to the result of the reduction:

(defn xf []
  (fn [rf]
    (fn
      ([] (rf))
      ([result] (rf result :foo))
      ([result input]
       (rf result input)))))

(sequence (xf) [1 2 3])

In Clojure, the above code yields

'(1 2 3 :foo)

. In ClojureScript, it results in an infinite loop. The same happens with `eduction`.
However,

(into [] (xf) [1 2 3])

doesn't produce an error.

Environment

None

Attachments

CLJS-2034.patch

12 May, 2017

Activity

Mike Fikes

July 18, 2017 at 1:37 PM

See regression in CLJS-2258.

David Nolen

May 12, 2017 at 9:53 PM

fixed https://github.com/clojure/clojurescript/commit/d93c4356e7ab78743ae66d8cffe8df54869f0be3

António Monteiro

May 12, 2017 at 9:46 PM

The implementation of transducers in ClojureScript tracked an old counterpart in
the Clojure codebase. This patch addresses the change introduced in the
following commit to Clojure, which replaced `LazyTransformer` with
`TransformerIterator`, effectively making the transducer behavior akin to the
one in Clojure.

https://github.com/clojure/clojure/commit/c47e1bbcfa227723df28d1c9e0a6df2bcb0fecc1

Attached patch with fix and test.

António Monteiro

May 12, 2017 at 8:13 PM

I'm looking into fixing this one.

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Completed

Details

Assignee

David Nolen

Reporter

António Monteiro

Labels

transducers

Patch

Code and Test

Fix versions

1.9.655

Priority

Minor

Created May 12, 2017 at 6:27 AM

Updated July 18, 2017 at 1:37 PM

Resolved July 18, 2017 at 1:37 PM