[erlang-questions] Infix function and user-defined operators

Richard O'Keefe <>
Tue Jan 8 14:53:01 CET 2019

The Haskell convention for user-defined operators is `name`  .
I don't see any point in inventing a new one.
I note that
(a) http://mlton.org/InfixingOperators shows a relatively simple
scheme for ML that would fit Erlang without too much strain.  It
starts with a warning that operator properties are not part of
module interfaces.  This was a problem in Prolog too, and I
surmise that it may have been the reason for not having user-
declared operators in Erlang.
(b) In F#, the type and precedence of a user-defined operator
are determined by its first character.  See
(c) ECMA Eiffel 8.28.5 puts all unary user-defined operators at the
same precedence level and all binary user-defined operators at another
precedence level.  Some other Eiffel dialects followed the same rule as
F#.  The (b) and (c) rules appear to also be related to not having
operator properties in signatures/classes/modules/whatever.

More years ago than I care to admit, I wrote an extended
Prolog parser that allowed user-defined "operators" like
"N of L are V" or "at least N of L are V".  It was based
on Vaughan Pratt's CGOL; see

On Tue, 8 Jan 2019 at 04:56, Dmitry Kolesnikov <>

> Hello Community,
> Now and then, I am missing an infix notation in Erlang. There was a great
> discussion about this subject decade and half ago but I do not think
> anything is changed [1].
> I am testing and stretching limits of functional abstracts in Erlang as
> part of my pure functional and generic programming exercises [2]. I’ve
> decided to experiment with Infix function via parse-transform.
> The parse_transform feature implements a syntax sugar for infix, which is
> compiled into valid Erlang code using corresponding function at
> compile-time. To apply a function using infix notation, we enclose its name
> in slash characters (/). This allows us to use any arity 2 functions as
> infix operators.
> ```
> -compile({parse_transform, infix}).
> 1 /plus/ 1.
> F /lists:map/ [1, 2, 3].
> ```
> Right now, I am working on this feature here
> https://github.com/fogfish/datum/pull/64, you can find more detailed
> description there, code, etc.
> I would appreciate for any feedback, suggestion from the community.
> Does it sounds any usable, still desired or total braindead?
> What other use-case/applications you might imagine for infix notation?
> Best Regards,
> Dmitry
> References
> 1. http://erlang.org/pipermail/erlang-questions/2004-March/011929.html
> 2. https://github.com/fogfish/datum
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