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SML AST Checker

Based largely off of sml-style-check and further improvements seen in here.

Currently there are two main utilities that can be used. A style checker, which essentially walks the AST of a given file and looks for specific patterns, and a TailRecursion checker, which takes an inputed AST and identifies all the (expressions variable) declarations and classifies them as to whether they use recursion, tail recursion, or no recursion.

The style checker can be used in two different ways:

  • One can use the visible Grader structures to implement the style grader into and autograding framework.
  • One can use the Top and Run and the ./smlnj to check files before they are used in the REPL.

Setup

This is currently used and tested using Standard ML of New Jersey v110.99, it can potentially work on some other version, but these are untested.

We use the smackage packages numbers and autograding. Here is a brief guide to setting up smackage (with these packages):

  1. Run the following commands:

    git clone https://github.com/standardml/smackage.git
cd smackage
make smlnj
bin/smackage

    If this all works correctly, this should display:

    Smackage 1.4.5
Usage: smackage <command> [args]
...

  2. In ~/.bashrc or ~/.zshrc, put

    export PATH="$HOME/.smackage/bin:$PATH

    Then restart your terminal (or use source).

  3. Run these commands:

    bin/smackage refresh
bin/smackage make smackage smlnj
bin/smackage make smackage install
which smackage

  4. Make a file in your home directory called .smlnj-pathconfig and put the following inside the file:

    SMACKAGE .smackage/lib

  5. Set-up the required packages:

    smackage source typeclasses git https://github.com/ProjectSavanna/typeclasses.git
smackage source result git https://github.com/ProjectSavanna/result.git
smackage source numbers git https://github.com/ProjectSavanna/ml-numbers.git
smackage source autograding git https://github.com/ProjectSavanna/autograding.git

  6. Run these, so that smackage can install the autograding package and all the relevant dependencies:

    smackage get autograding

  7. As a check, run smlnj '$SMACKAGE/numbers/v1/sources.cm'. When evaluating Natural.fromInt 5 you should get this result:

    Standard ML of New Jersey (64-bit) v110.99 [built: Thu Dec 24 11:47:23 2020]
- Natural.fromInt 5;
val it = Succ (Succ (Succ (Succ (Succ Zero)))) : Natural.t

  8. In the future, for updates, run smackage refresh and smackage update.

Style Checker

The style checker is organised into a number of rules which we can then check depending on what is considered acceptable style for any given homework problem. It can be loaded in use sources.cm.

A list of all the existing style rules can be found in the AllRules structure defined (here)[main/rules/all_rules.sml], specificially the datatype rule defines a list of all the rules supported.

  • Each of these rules is associated with a (checker)[checkers], which defines how to actually check for the rule
  • If a new rule is to be added, a new checker should be written and the rule datatype should be expanded, along with it being registered in the lists further down in the AllRules structure.

The functors Rules, EnableRules, and DisableRules, provide different ways to create a structure ascribing to RULES, which can then be passed into the CustomStyleGrader functor to create a grader.

If the style checker needs to be used with the REPL, there also exists the functor Run, which takes in a structure ascribing to RULES, and Top which provides an example of how one might use Run.

The Top structure provides val run : string list -> int, which takes in a list of files (possibly cm files) and evaluates to the number of issues, printing out associated information. It also provides a val export : unit -> unit function which dumps a heap image called limit-sml.amd64-darwin (the extension my differ depending on your OS) which can be passed a list of files to check. The rules used by this can be adjusted by changing how the Use structure is defined within Top.

The ./smlnj script passes your files into the heap image (the name may need to be updated) and evaluates them. If no style errors exists, then it passes them into the sml REPL (with rlwrap if installed).

Tail Recursion Checker

The Tail Recursion checker identifies all the (expression-level) declarations within the file, and defines whether they use recursion, tail recursion, or are non recursive. It can be used through the tailrec.cm file.

For general usage, the structure BasicClassifier is exported. This defines two main driving functions, classifyAst and simpleClassifyAst. They both take in an Ast.dec and output a list of bound variables and thier classifications as NonRecursive, Recursive, or TailRecursive (the first function also outputs the declaration where it is bound as well as region information).

For testing/playing around, it is likely better to use the testing.cm file and then defining:

val test = BasicClassifier.simpleClassifyAst o Parse.parseFile
val results = test "tests/tailrec/basic.sml"