Poly/ML

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711 discussions

Type Constraints and Overloading
by Duke Normandin 02 Mar '26

02 Mar '26

Taken from Paulson's book: Chap2.4 A) fun square x = x * x; > Error- Unable to resolve overloading for * I understand the above! B) fun square(x : real) = x * x; I understand: x is declared as a real C) fun square x = x * x : real; I see this as declaring a function w/o parentheses AND that the r_result_ is a 'real' I have a problem with this declaration: D) fun square x : real = x * x; I see this as declaring a function w/o parentheses, AND declaring x to be a 'real' I do NOT see/understand that this syntax indicates that the type of the _result_ is a 'real' I suppose that I'm free to ignore D) and use the more IMHO intuitive C) declaration. I thought that I'd ask to make sure that I wasn't missing something in the D) one. TIA .... -- Duke

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Quick Question About polyml.org and Its Current Status
by Kimmy Trango 24 Feb '26

24 Feb '26

Hello, Kimmy here. I lead Community Outreach at Dotcom Monitor, and I have been exploring long standing programming language implementations and research driven projects. Poly ML really stood out to me. It is impressive to see a mature and high performance implementation of Standard ML that has supported both academic research and real world development for many years. Projects like Poly ML play an important role in advancing language design and functional programming. It clearly reflects deep technical expertise and sustained community effort. I wanted to ask, is polyml.org and the Poly ML project still actively maintained? At Dotcom Monitor and LoadView, we work closely with long running technical and open source projects. We aim to support the community in ways that are practical and genuinely helpful. For context: https://www.dotcom-monitor.com/sponsoring-open-source-projects/ https://www.loadview-testing.com/scholarship/ If the project is still active, we would be glad to explore the possibility of offering a small corporate contribution to help support its continued development. I would love to hear your thoughts. -- Cheers, *Kimmy Trango*Community Outreach Assistant Dotcom-Monitor <https://www.dotcom-monitor.com/> | Monitor > Repair > Optimize LoadView <https://www.loadview-testing.com/> | Flexible Load Testing from the Cloud

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variable shadowing
by Duke Normandin 25 Jan '26

25 Jan '26

I think that I almost understand "shadowing", maybe ... val pi = 3.14159; fun area (r) = pi*r*r; area 2.0; => 12.56636 So far so good ... re-declare pi ... val p1 = 0.0; Here is where things get blurry for me. When/how is the *new* pi available? Is it only available if re-declared in a *block* of code, making it local to that block and therefore usable there and only there? After re-declaring pi above, executing the "area" function uses the original pi. I get that! What I'm not sure of is how to use the re-declared pi. TIA ... -- Duke

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"symbolic" identifier names
by Duke Normandin 21 Jan '26

21 Jan '26

Reading Paulson!! Right ON!! lol [quote] ML also permits symbolic names. These consist of the characters ! % & $ # + - * / : < = > ? @ \ ˜ ‘ ˆ | Names made up of these characters can be as long as you like: ----> $ˆ$ˆ$ˆ$ !!?@**??!! :-|==>-># Certain strings of special characters are reserved for ML’s syntax and should not be used as symbolic names: : | = => -> # :> A symbolic name is allowed wherever an alphabetic name is: val +-+-+ = 1415; > val +-+-+ = 1415 : int [/quote] What purpose would this cryptic-tude serve? Obfuscation? Seeding brain cancer? What? Or do most of you simply ignore this allowance? Enjoying Paulson!! And so far, Poly&Paulson are a team!! :) -- Duke

2 2

Type error in function application
by Duke Normandin 21 Jan '26

21 Jan '26

This function: fun divide (x: real, y: real) = if y = 0.0 then raise DivByZero 5 else x / y; is taken from: "Beginner's Guide to Standard ML" It's part of a "calculator" program included in the document. I'm using: $ poly --use ./calc.sml Poly/ML 5.9.2 Release and it chokes and quits at line 4 on the above function. I made no typo! So! What now? Why doesn't Poly/ML not like that code? TIA ... -- Duke

5 8

First step woes
by Duke Normandin 18 Jan '26

18 Jan '26

From: INTRODUCTION TO POLY D.C.J. Matthews,May 1982 Computer Laboratory, University of Cambridge [quote] > begin # print("Hello"); # print(" again") # end; Hello again [/quote] but I get: [quote] > begin # print("hello"); poly: : error: Value or constructor (begin) has not been declared Found near begin print ("hello") Static Errors > [/quote] if I remove the semi-colon, it lets me enter the rest of the code, but chokes after I enter `end;'. Has the syntax changed since the book was written, or am I doing something wrong? TIA ... -- Duke

3 3

Defining a function
by Duke Normandin 18 Jan '26

18 Jan '26

Noob to SML & PolyML here! Trying to solve "exercism" SML track. Lesson2 wants me to create a function as: fun leapyear blah blah I have a bunch of pdf docs for sml-nj, poly/ml etc and none show that syntax to create a function. What am I missing? TIA ... -- Duke

2 3

ML Basis
by vqn 31 Oct '25

31 Oct '25

Hello, Over the past few months, I have been working on an implementation of the ML Basis system for Poly/ML. It supports the complete mlb spec and is available both as a library and a cli tool: https://github.com/vqns/polymlb On a side note, I have been trying to implement incremental compilation by caching compiled .mlb files (i.e compiler namespaces) and exporting and reimporting them through {save,load}ModuleBasic. I have however been running into the issue that exporting each .mlb to a different on-disk module causes opaque types mismatch when reimporting them. What would be the reason for that? I have managed to work around it by exporting everything to the same file, but that result in a fairly large cache, e.g ~45mb for smlfmt (1.2mb executable, 15k loc). I suppose the reason for that is that I export the basis library as well, but I'm not sure there is a solution for that.

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tuple indexing: 0-based or 1-based?
by Gabriel Scherer 28 Oct '25

28 Oct '25

Dear SML people, There is an OCaml feature proposal by Alistair O'Brien that would finally introduce tuple indexing in OCaml -- we currently have only whole-tuple pattern matching: RFC: https://github.com/johnyob/ocaml-RFCs/blob/tuple-projections/rfcs/tuple_pro… discussion: https://github.com/ocaml/RFCs/pull/57 Of course this raises the Very Important Question of whether indexing should be 0-based or 1-based. The argument in favor of 0-based is that it is what we use for arrays, so more consistent, standard in most programming languages. The argument in favor of 1-based is that it is arguably more intuitive (but the inconsistency with arrays weakens this claim noticeably), and that SML uses it. Question: you have a lot more experience using tuple indexing. In your opinion, if this was to be decided again for a new system (no backward-compatibility concerns), would you still recommend using 1-based indices, or would you be more in favor of 0-based indices? P.S.: You may be amused to learn that OCaml recently introduced "labeled tuples" (looking like `(x:1, y:2)` in expressions and `(x:int * y:int)` in types), which are basically a restricted version of SML structural records -- type inference does not try very hard and requires an annotation in practice. P.P.S: Is there still a mailing-list for the SML/NJ crowd? All I could find were github discussions (https://github.com/orgs/smlnj/discussions) and an invite-only Zulip.

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Reusing PolyML's runtime system
by bloop36＠protonmail.com 26 Sep '25

26 Sep '25

Hello everyone, I have just created an ML compiler to experiment with some ideas. The compiler is missing native compilation and a proper REPL, so I'm thinking of reusing the existing backend and runtime system of PolyML to build a complete compiler system. I believe the design of PolyML is modular enough for new frontends to be attached to the existing backend, but I have no idea where to start. Could someone point me in the right direction please? Shuhan HE

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