sml-msgfmt

A message plural-form selector for Standard ML with locale-aware CLDR cardinal plural categories. Maps a count to its plural category (one, few, many, other, ...) under a named locale rule, and picks the matching pre-rendered string.

API

datatype category = Zero | One | Two | Few | Many | Other
datatype rule = English | French | Slavic | Other'

val select       : rule -> int -> category    (* count -> CLDR category    *)
val categoryName : category -> string          (* "one", "few", "many", ... *)
val selectByName : rule -> int -> string        (* categoryName o select     *)

exception NoOther
val cardinal : rule -> int -> (category * string) list -> string

(* legacy: argument order is (n, one, other, few) *)
val plural : int -> string -> string -> string -> string

Rules

rule	categories
English	one (n = 1), other
French	one (n = 0 or 1), other
Slavic	one (n = 1), few (n mod 10 in 2-4 and n mod 100 not in 12-14), many
Other'	always other

MsgFmt.select MsgFmt.English 1    (* One   *)
MsgFmt.select MsgFmt.English 2    (* Other *)
MsgFmt.select MsgFmt.French 0     (* One   *)
MsgFmt.select MsgFmt.Slavic 3     (* Few   *)
MsgFmt.select MsgFmt.Slavic 5     (* Many  *)
MsgFmt.select MsgFmt.Slavic 22    (* Few   *)

cardinal: pick a pre-rendered form

cardinal r n forms selects the string whose category matches select r n, falling back to the Other entry (which is required; its absence raises NoOther).

val forms = [(MsgFmt.One,  "1 plik"),
             (MsgFmt.Few,  "%d pliki"),
             (MsgFmt.Many, "%d plikow"),
             (MsgFmt.Other,"%d plikow")]

MsgFmt.cardinal MsgFmt.Slavic 1 forms   (* "1 plik"    *)
MsgFmt.cardinal MsgFmt.Slavic 3 forms   (* "%d pliki"  *)
MsgFmt.cardinal MsgFmt.Slavic 7 forms   (* "%d plikow" *)

Legacy plural

(* note the argument order: n, one, other, few *)
MsgFmt.plural 1 "1 file" "N files" "a few files"   (* "1 file"      *)
MsgFmt.plural 3 "1 file" "N files" "a few files"   (* "a few files" *)
MsgFmt.plural 9 "1 file" "N files" "a few files"   (* "N files"     *)

Scope and limitations

• Only cardinal plural rules for a handful of representative locales (English, French, Slavic/Polish-style) are built in; ordinal rules and the full CLDR locale set are out of scope.
• select operates on integer counts only — no decimal/fraction visible-digit operands (v, f, t), and no number interpolation, {count} placeholder substitution, gender, or message catalog. You supply already-formatted strings.

Example

make example builds and runs examples/demo.sml, which runs selectByName over representative counts for the English, French, and Slavic rules, then shows cardinal picking a pre-rendered form and the legacy plural helper (output is byte-identical under MLton and Poly/ML):

selectByName over counts [0,1,2,3,5,11]:
  English: 0=other 1=one 2=other 3=other 5=other 11=other
  French: 0=one 1=one 2=other 3=other 5=other 11=other
  Slavic: 0=many 1=one 2=few 3=few 5=many 11=many

cardinal with pre-rendered forms (Slavic rule):
  1 -> one item
  2 -> a few items
  5 -> many items

legacy plural helper plural(n, one, other, few):
  plural 1 -> one
  plural 2 -> few
  plural 5 -> other

Installing with smlpkg

smlpkg add github.com/sjqtentacles/sml-msgfmt
smlpkg sync

Reference from your .mlb:

lib/github.com/sjqtentacles/sml-msgfmt/msgfmt.mlb

Building and testing

make test        # MLton
make test-poly   # Poly/ML
make all-tests   # both
make clean

Project layout

sml.pkg
Makefile
lib/github.com/sjqtentacles/sml-msgfmt/
  msgfmt.sig
  msgfmt.sml     CLDR cardinal categories + locale rules + selection
  msgfmt.mlb
test/
  test.sml       category selection, cardinal, legacy plural

License

MIT. See LICENSE.