frou / smlfmt

A custom parser/auto-formatter for Standard ML

parse-sml

A custom parser and code formatter (smlfmt) for Standard ML, with helpful error messages.

Supports SML source files (.sml, .sig, .fun, etc.) as well as MLBasis compilation files (.mlb) using MLton conventions, including MLBasis path maps.

Examples: Error Messages

Examples: Code Formatting

The formatter generally handles blank lines and multiline comments in a reasonable way:

Input:

fun fib n = (* everyone loves
             * fibonacci numbers *)
    if n < 2 then n
 else fib (n-1)
  + fib (n-2)

val f5 = fib 5
val f10 =
  fib 10
val f15 = fib 15

Output:

fun fib n =
  (* everyone loves
   * fibonacci numbers *)
  if n < 2 then
    n
  else
    fib (n - 1) + fib (n - 2)

val f5 = fib 5
val f10 = fib 10
val f15 = fib 15

Build and run

You need mlton installed.

Do make and then pass either a .sml file or a .mlb file, for example:

$ make
$ ./smlfmt --preview src/smlfmt.sml

Command-line options

--force skips overwrite confirmations.

--preview also prints any formatted code to stdout, with syntax highlighting (if shown on terminal supporting ANSI colors).

--preview-only is the same as --preview, but also skips writing to file. (This is incompatible with --force.)

-mlb-path-var '<key> <value>' for handling path variables, similar to MLton's path maps.

-ribbon-frac <real> (default 1.0) controls pretty-printing. The ribbon-frac (between 0 and 1) controls how dense each line is, excluding indentation. Low ribbon-fracs will have very little non-whitespace content on each line, whereas high ribbon-fracs will attempt to fill the line as much as possible. Default = 1.0

-max-width <int> (default 80) controls pretty-printing. This is the desired maximum number of columns in each line.

-indent-width <int> (default 2) is the desired number of spaces used in the formatted output.

-tab-width <int> (default 4) informs the pretty-printer of the intended tab-width for the input source. Typically this doesn't matter, but there are some cases where a particular tab-width can influence the vertical alignment of multiline comments and strings. (See discussion in issue #28 for more details.)