Check syntax of Standard ML program using Poly/ML without executing the program

polyml-syntax-check.sml

(* Check for syntax errors and type errors in a Standard ML file without
 * executing the program. Tested in Poly/ML 5.9 on Ubuntu 20.04.
 *
 * To check for the existence of errors in a Standard ML file using Poly/ML, it
 * is sufficient to use `PolyML.compiler (TextIO.input1 inStream, [])`. However,
 * that will not show line and column numbers when there are errors or warnings.
 * This program adds line and column numbers to the error and warning messages.
 *
 * Usage:
 *   poly --script this-file.sml file-to-check.sml
 *
 * Behavior:
 *   * Prints warnings and errors to standard output.
 *   * Exits with exit code 1 if there are errors, exits with exit code 0
 *     otherwise.
 *
 * To print to standard error instead of standard output, add this to the
 * compiler parameter list in the call to PolyML.compiler:
 *   PolyML.Compiler.CPOutStream (fn s => (TextIO.output (TextIO.stdErr, s);
 *                                         TextIO.flushOut TextIO.stdErr))
 * *)

fun getLineChars inStream =
  (* Limitation: TextIO.inputLine will raise the "Size" exception if the line is
   * longer than String.maxSize. *)
  case TextIO.inputLine inStream of
    NONE => NONE
  | SOME s => SOME (explode s)

fun checkFile filePath =
  let
    val lineNum = ref 0
    val colNum = ref 0
    val curLine = ref []
    val ins = TextIO.openIn filePath
    fun getChar () =
      case !curLine of
        [] =>
          (case getLineChars ins of
             NONE => NONE
           | SOME (c::cs) =>
               (curLine := cs;
                lineNum := !lineNum + 1;
                colNum := 1;
                SOME c)
           | SOME [] =>
               (lineNum := !lineNum + 1;
                getChar ()))
      | (c::cs) =>
          (curLine := cs;
           colNum := !colNum + 1;
           SOME c)
  in
    (ignore o PolyML.compiler)
      (getChar, [PolyML.Compiler.CPFileName filePath,
                 PolyML.Compiler.CPLineNo (fn () => !lineNum),
                 PolyML.Compiler.CPLineOffset (fn () => !colNum)])
  end

val () = case CommandLine.arguments () of
           ["--script", _, fileToCheck] => checkFile fileToCheck
         | _ => raise (Fail "Invalid command line arguments")