Stream: Archive Mirror: Isabelle Users Mailing List

Topic: [isabelle] Why is Monad_Syntax.bind right and not left as...


view this post on Zulip Email Gateway (Aug 22 2022 at 20:07):

From: Martin Desharnais <martin.desharnais@gmail.com>
Dear Isabelle users,

I recently discovered the HOL-Library.Monad_Syntax theory with its
(>>=) and do-notation. While defining an inductive predicate using
multiple bind operations, I encountered the following error message.

Unresolved adhoc overloading of constant bind

I minimized the my code until I noticed that the error only occurs with
two or more binds and can be resolved by adding parenthesis on the left
operands.

theory Scratch
imports Main "HOL-Library.Monad_Syntax"
begin

context
fixes f :: "nat ⇒ 'a ⇒ 'a option" and x :: "'a"
begin

declare [[show_variants]]

term "Some x >>= f 0"
(* "Option.bind (Some x) (f 0)" :: "'a option" *)

term "Some x >>= f 0 >>= f 1"
(* Unresolved adhoc overloading of constant bind *)

term "((Some x) >>= f 0) >>= f 1"
(* "Option.bind (Option.bind (Some x) (f 0)) (f 1)" *)

end

end

I checked the source code of Monad_Syntax and noticed that it is
declared as infixr ">>=" 54. I was quite surprised because such a
choice requires one to add extra parenthesis in what seem to be common
cases and the traditional Haskell (>>=) operator itself is left associative.

What is the reasoning for the Isabelle (>>=) to be right and not left
associative? What are situations where it makes more sense?

Best regards,
Martin Desharnais
signature.asc

view this post on Zulip Email Gateway (Aug 22 2022 at 20:09):

From: Christian Sternagel <c.sternagel@gmail.com>
Just as another data point: I also don't remember any specific reasons
for >>= being infixr.

And, like sel4, in IsaFoR we mostly use do-notation (683 occurrences)
over explicit binds (20 occurrences).

cheers

chris

view this post on Zulip Email Gateway (Aug 22 2022 at 20:10):

From: Tobias Nipkow <nipkow@in.tum.de>
Dear Martin,

We have made "bind" left-associative now, which is customary and makes more
sense. Thank you for notifying us.

Tobias
smime.p7s


Last updated: Mar 29 2024 at 01:04 UTC