Standard ML of New Jersey Release Notes

SML/NJ HOME: https://smlnj.org
FILES: https://smlnj.org/dist/working/2026.3/

Summary

This release contains over 100 (mostly minor) bug fixes for issues identified by Claude and reported by Skye Soss. There are also a number of other bug fixes and improvements.

Details

Compiler

Added constant folding for the rotation operators
Switch to using mixed records for live variables in InvokeGC.
Switch to using mixed records to represent closures that contain both uniform and raw free variables.
Switch to using mixed records when spilling excess function arguments to the heap.
Add sanity checking for the various integer controls in the Control.Print structure. For example, the REPL will now always print the top-most part of a value, even when the Control.Print.printDepth flag is less than 1.
for the amd64 (a.k.a. x86-64) target, we now assume a Haswell processor.

Runtime System

Changed the heap layout to include an arena for "mixed" records.
The codegen library now zeros the padding in the object-file, which should make builds more deterministic (and fixes the problem of not being able to compile to a fixed point).

Basis Library

A large number of *Basis Library bugs were fixed (see the list below for details).

SML/NJ Library

A large number of SML/NJ Library bugs were fixed (see the list below or the smlnj-lib/CHANGES file for details).

The original HTML library has been renamed to HTML3 (the CM tilf is now html3-lib.cm). The modules in the library have not been renamed.
Added listKeys function to HASH_TABLE and MONO_HASH_TABLE signatures.
Added the Timestamp module to the Utility library. This module supports generating timestamps that respect the SOURCE_DATE_EPOCH environment variable.

ML-LPT

Fixed regression in ml-lex-mode (Issue #463)
Fixed a bug in handling grammars where there is no %start declaration, but the first nonterminal is declared as an %entry.
Fixed a bug where the code generated by ml-antlr is invalid

Concurrent ML

Fixes to the Barrier module.
Fixed a scheduling issue in recv.
Fixed several issues in the TraceCML module.
Fixed the behavior of CML's OS.Process.terminate to match the Basis Library specification.
Fixed TextIO.input1, TextIO.inputLine, and BinIO.input1 to restore the mVar on end of file.

Installation

A number of changes have been made to improve reproducibility of builds.

Bugs

Here is a list of the issues and pull requests that are closed with this release.

Issue	Description
142	Vector pattern causes integer variables to be printed as abstract types
232	Spurious use of polyEqual
339	Build failure - unable to find PerID
361	Make `build.sh` script more portable
364	Fix `Word.countTrailingZeros`
365	Fix position calculation of `funsig` token
366	Fix the printing of vector patterns
367	Fix the pattern match to reference `REF` dcon
368	compiler throws an error upon invalid opaque signature match
370	The SExp parser re-parses top-level quoted symbols
371	The SExp parser parses negative numbers as symbols
373	JSONParser.parse does not ensure `0` is not followed by a digit
375	`UnixEnv.addToEnv` does not replace existing keys
376	ThompsonEngine does not implement `^`
377	ThompsonEngine can’t match `Interval (r, m, SOME m)`
378	`UTF8.map` does not do anything
379	`UTF8.exists` always returns `true`
380	`CharMap.mkCharMap` creates a too-small array
381	Rand48’s incorrect implementation results in periodic results
382	`HashSetFn.filter` does not reset the number of elements if it removes everything
383	`ListMapFn.all` always return `false`
384	`IntervalSetFn.add` operation doesn’t properly merge consecutive ranges
385	`Hash2TableFn.insert` can corrupt the table
386	`EditDistance.distance` uses the wrong stride
387	`Controls.mkOptionFlag` evaluates toggled value eagerly
388	`Format.LEFT` justifies text to the right
389	`Format.format` raises `Option` instead of `BadFormat` on invalid format
390	line break cutoff is one character too strict in PP library
391	pretty-printing `maxDepth` is controlled by `maxIndent`
392	ANSI background color styles are not properly popped
393	`Posix.ProcEnv.uname` crashes on syscall failure
394	`Int64.int` value is sometimes corrupted
398	`IntListMap.findAndRemove` raises exception on failure
399	`HashTable.findAndRemove` does not update `numItems`
400	`Word8Buffer.sub` allows invalid indices and throws on valid indices
401	`Word8Buffer.copy` throws exception on valid input
402	`Array.tabulate` calls its function even on invalid input
403	`Substring.isSubstring` returns false when given empty strings
404	`Date.fmt` ignores `%%` if followed by a letter
405	`Real.rem` produces incorrect results for non-finite arguments
406	`CharVectorSlice.getVec` returns a slice containing the entire underlying vector
432	`Hash.string'` does not hash the first character
433	The hash table in the `Atom` module is never resized
434	`EditDistance.distance` treats transposition as free
437	Calling `OS.IO.poll` function with duplicate descriptors can result in a crash
438	Socket `recv` can trigger runtime crash
440	`ParserComb.skipBefore` returns `NONE` when it reaches EOF
440	`Time.scan` doesn’t backtrack after seeing `.`
442	`Int64.div` constant folding suppresses `Overflow` exception
443	`NetHostDB.scan` raises `Overflow` on parse error instead of returning `NONE`
444	`Int32.abs` of `Int32.minInt` should raise `Overflow`
445	`IntInf.scan StringCvt.BIN` accepts hex prefix
446	`Real.toDecimal`/`Real.fromDecimal` don’t round-trip
447	`StringCvt.skipWS` does not skip form feeds, returns, or vertical tabs
448	`Vector.update` does not raise `Subscript` on out-of-bounds index
449	`TextIO.inputAll` fails with 'divide by zero' error on empty stream
450	`LargeInt.fmt StringCvt.HEX` produces lowercase hex digits
451	`Date.fromString` does not skip leading whitespace
452	`Date.fromTimeUniv o Date.toTime` adds 12 hours to the date
453	`Math.pow` is unusually inaccurate
454	`IntInf.pow` does not handle negative exponents correctly
456	`Timer.checkCPUTimer` double-counts garbage collector time
463	`ml-ulex --ml-lex-mode` generates duplicate `yystart_state` datatype declaration
465	Unbound exception identifier causes compiler bug
466	Add type info in `FLINT/fcontract` to generate well-formed FLINT
470	Ignore inherited `SMLNJ_HOME` during source builds

We also fixed the following bugs that did not have issues associated with them (or were bug fixes ported from the legacy repository):

updated the unused-variable checker for changes to the Absyn.exp datatype
avoid Overflow exceptions when #line comments are very large (there is now an upper bound on the allowed line/column numbers)
fixed various boundary cases in the Array2 structure.
Socket.Ctl.getRCVBUF and Socket.Ctl.setRCVBUF controlled the SNDBUF
the PackReal64 structures had the byte orders backwards
Word.-(0wx7FFFFFFFFFFFFFFF, x) produced incorrect results
The Real.scan function was too permissive
Fixed dangling pointer bug when SetVMCache frees memory objects
Fixed "unbounded" traversal of cyclic values when the printDepth < 0
Rewrote Real64.rem to produce exact results.
The compiler no longer raises overflow when checking real literals with excessively large exponents
The order of the "don’t route", "peek", and "out-of-band" flags for socket I/O operations was backwards in the runtime system.
Socket.recvVecFrom can corrupt the address data.
Fix edge case of primitive readers/writers with chunk sizes < 1.
Fixed Date.fromTimeUniv and Date.fromTimeLocal on negative time values.
Fixed an issue where large strings were getting allocated as bytearrays, which broke the REPL printing.
(Mostly) fixed the behavior of rounding reals to integers. The ceiling, floor, and truncation functions are correct, but round and realRound do not break ties correctly.

Supported systems

We believe that SML/NJ will build and run on the following systems, but have only tested some of them:

Architecture

Operating System

Status

AMD64

macOS 11 (Big Sur)

macOS 12 (Monterey)

macOS 13 (Ventura)

macOS 14 (Sonoma)

macOS 15 (Sequoia)

Tested

macOS 26 (Tahoe)

Ubuntu 20.04.6 LTS

Tested

Ubuntu 22.04.2 LTS

Tested

ARM64

macOS 11 (Big Sur)

macOS 12 (Monterey)

macOS 13 (Ventura)

macOS 14 (Sonoma)

macOS 15 (Sequoia)

macOS 26 (Tahoe)

Tested

macOS 27 (Golden Gate)

Tested

Linux