As with a lot of things, I think I know how to write this, but I figured I’d ask around, b/c I can’t find it by googling, and perhaps somebody here knows where to look. I’m translating some Python code to OCaml, and it’s going really well. But I have come across a function that has a complex if-t…

Exceptions will probably make your code most direct-style and easiest to follow, like you pointed out. I think the closest I know to a pre-existing monad for what you want is the result type, and the Result.bind function, although I’m not sure if it fits your use case since the two cases are Ok and…

You can use local exception: let exception Exit in try ... with Exit -> Nice and clean. A bare-bone early exit monad could be: module Pipeline = struct type ('a, 'b) t = Continue of 'a | Terminal of 'b let pure v = Continue v let exit v = Terminal v let bind m f = match m with …

Honestly, I’m surprised at myself that I didn’t just reach for exceptions for nonlocal exit and ref for the updatable variables from the jump, not bothering to post to ask the question. Too much time spent hacking in pure functional OCaml.

You don’t even need ref: let exception Exit of int in try raise (Exit 42) with Exit c -> c

[image] Chet_Murthy: Also, I wondered if there was a “bestiary” of OCaml monad implementations … that might be useful to have. The most extensive collection of algebraic computational structures in OCaml I’m aware of is @xvw ’s preface .

haha yes, that’s what I did: let rec _closure self input (config : AC.t) configs ~currentAltReachedAcceptState ~speculative ~treatEofAsEpsilon = let exception EarlyReturn of bool in let currentAltReachedAcceptState = ref currentAltReachedAcceptState in try .... raise (EarlyRe…

This also exists in JaneStreet’s base library: [image] base v0.17.3 · OCaml Package base v0.17.3: Full standard library replacement for OCaml

I’m reminded of this PR that was submitted to BAP a while back: rewrites knowledge and primus monads by ivg · Pull Request #1361 · BinaryAnalysisPlatform/bap · GitHub The “double-barreled” CPS style here seems like a nice, general way to accomplish this.

Aha, very nice! I am reminded of … John Reppy writing this sort of CPS transformer back in the late 80s as part of SML/NJ. Two continuations, one the normal continuation, one the exception continuation.

I thought Andrew Kennedy came up with the double-barrelled CPS idea and terminology in his “Compiling with Continuations, Continued” paper, but it’s interesting that the idea apparently predates that paper by two decades! I think I probably misremembered the credit from this article, which cites An…

Looking around for a monad for dealing with early "return"

Ecosystem

shonfeder July 16, 2026, 5:41pm 13

I think that must be at What are your feelings about : mlton,mosml,polyml,smlnj - #5 by Chet_Murthy ? I love reading this history

Topic		Replies	Views
What is the programming pattern with multiple if else branching Learning	28	982	December 15, 2025
Early termination in folds Ecosystem design	18	1108	February 17, 2025
IO Monad for OCaml Learning effects	13	7619	November 8, 2019
Pattern matching syntactic sugar Learning	11	640	April 18, 2025
Maybe monad in ocaml Learning	2	2326	July 25, 2022

Looking around for a monad for dealing with early "return"

Related topics