Coding Conventions - SML

This is unpleasant, since each compiler has its own conventions. And it seems only Poly/ML really runs on a Raspberry Pi.

Poly/ML expects a fun main () = ... somewhere. When compiled, Poly/ML will interpret the main() function as the entry point.

For MLton, I believe, it will only run a function if it's executed. That is to say, we need to have val _ = main(); somewhere, if we want MLton to execute main(). But Poly/ML doesn't like this, and won't compile it happily.

If we want to support compiling with both Poly/ML and MLton, we need to also have main.sml file which consists of a single line:

(* main.sml *)

val _ = main ();

MLton will compile everything, including main.sml, while Poly/ML will just omit main.sml from compilation.

The following is what Chris Okasaki does in his book, Purely Functional Data Structures, and it works well.

Reserved keywords (like of, struct, fun, let, in, val, etc.) are written in bold.

Datatype constructors are written in small-caps.

Signatures are typeset by:

• Step 1: convert SCREAMING_SNAKE_CASE into Pascal snake case Screaming_Snake_Case
• Step 2: delete underscores, converting Screaming_Snake_Case into ScreamingSnakeCase
• Step 3: typeset the result of step 2 in small-caps.

Type variables (the 'a in declarations like datatype 'a Foo), including the apostrophe, are converted to lowercase Greek counterparts (so we would get: "datatype \(\alpha\) Foo").

Comments are italicized or slanted.

Everything else seems to be typeset "as expected".

A kludge which accomplishes the typesetting for signatures (the only downside is that I need to manually add signature names to the morekeywords={[2]...} parameter):

\documentclass{article}
\usepackage{mfirstuc}
\makeatletter


% I need to do something like
% https://tex.stackexchange.com/a/448770/14751
% to transform the "\lst@um_" back to "_"

\def\@Screaming@Snake@To@Pascal@Case#1\_#2\end@Screaming@Snake@To@Pascal@Case{%
  \makefirstuc{\MakeLowercase{#1}}%
\ifx#2\@empty\else\ignorespaces\@Screaming@Snake@To@Pascal@Case#2\end@Screaming@Snake@To@Pascal@Case\fi}

\newcommand\ScreamingSnakeToPascalCase[1]{%
  \ifx\@empty#1\else{\normalfont\scshape\@Screaming@Snake@To@Pascal@Case#1\_\@empty\end@Screaming@Snake@To@Pascal@Case}\fi}

% https://tex.stackexchange.com/questions/439396/listings-highlight-a-prefixed-keyword-starting-with-a-single-quote
\makeatother

\usepackage{listings}

\makeatletter

\def\@setlststyle{%
  \unskip\edef\lt@temp{\unskip\noexpand\ScreamingSnakeToPascalCase{\expandafter\the\lst@token\unskip\relax\unskip}}%
  \unskip\global\lst@token=\expandafter{\lt@temp}%
  \unskip\the\lst@token
}

\begingroup
\catcode`\_=11

\gdef\scsty#1{
  \unskip\edef\lsttokens{\the\lst@token}
  \unskip\global\lst@token={}
  \unskip\expandafter\replaceUM\lsttokens\noexpand\lst@um_\relax\@end
  \unskip\unskip\@setlststyle
}

\gdef\appendall#1\@endAppend{\unskip
  \global\lst@token=\expandafter{\the\lst@token#1}
}
\gdef\replaceUM#1\lst@um_#2\@end{\unskip
  \if\relax\detokenize{#1}\relax
  \else
    \ifx\relax#2
      \appendall#1\@endAppend
    \else
      \appendall#1\_\@endAppend
      \replaceUM#2\@end
    \fi
  \fi
}
\endgroup

\makeatother

\def\haskWildcard{\kern0.06em \vbox{\hrule width .5em}}
\lstset{
  columns=flexible,
  alsoletter={_},
  basicstyle = {\ttfamily},
  keywordstyle = [2]\scsty,
  morekeywords = [2]{SOME,NONE,GREATER,EQUAL,LESS,STRETCH_GOAL},
  keywordstyle = {\bfseries\sffamily},
  morekeywords={abstype,and,andalso,as,case,do,datatype,else,end,%
       eqtype,exception,fn,fun,functor,handle,if,in,include,infix,%
       infixr,let,local,nonfix,of,op,open,orelse,raise,rec,sharing,sig,%
       signature,struct,structure,then,type,val,with,withtype,while},%
   sensitive,%
   morecomment=[n]{(*}{*)},%
   morestring=[d]",
   literate={JOB}{{\ttfamily\scshape Job}}3 {'a}{{$\alpha$}}1 {'b}{{$\beta$}}1
               {\ o\ }{{$\circ$}}3 {+}{{$+$}}1 {/}{{$/$}}1 {*}{{$*$}}1 {=}{{$=$\ }}1
               {>}{{$>$}}1 {<}{{$<$}}1
               {\\\\}{{\char`\\\char`\\}}1
               {->}{{$\rightarrow$}}2 {>=}{{$\geq$}}2 {<-}{{$\leftarrow$}}2
               {|}{{$\mid$\ }}1 {\ _}{{\ \haskWildcard}}2  
}
\begin{document}


\begin{lstlisting}
signature STRETCH_GOAL = sig
  val will_work : bool;
  val issued : bool option;
end;

fun giveRaise (SOME true) = true
  | giveRaise _ = false;
\end{lstlisting}
\end{document}

SML-mode provides all the functionality we need. Just add to the init.el file:

(use-package sml-mode
  :ensure t
  :defer t)
(add-to-list 'auto-mode-alist '("\\.\\(sml\\|sig\\|fun\\)\\'" . sml-mode))

• Naming conventions in Standard ML, The Breakfast Post (blogpost)
• Standard ML and how I'm compiling it, The Breakfast Post (blogpost)
• Theory ML, Isabelle's coding conventions
• Symbol attempts to provide a minimal build tool for Standard ML