Symbol

A build tool for Standard ML

Symbol is a build tool for Standard ML. It's designed to work alongside and on top of existing SML build tools, like SML/NJ's CM and MLton's MLBasis files.

Here's a quick screencast to show off its features:

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Symbol's key features are:

• Designed to build executables

  Symbol builds and installs runnable executables for your project. With SML/NJ, these executables use heap images under the hood, while MLton generates linked binaries. These details are internal; the end result is always an executable that you can invoke from the command line.

• Low friction for collaborators

  Symbol's executable is designed to be checked into your project's version control. This means your collaborators do not have to install Symbol globally before they can build your project.

• Built on make

  As much as possible, Symbol uses make to cache previous build steps. Running symbol make a second time should usually be instant. All intermediate outputs are stored into a .symbol-work folder in your current directory, and it's always safe to delete this folder.

• Scaffold new projects

  The symbol new command is how you initialize new Standard ML projects. It prepopulates CM and MLBasis files and copies the Symbol scripts into your project, so you can jump write into your project.

• Convention over configuration

  Symbol infers information about your project from its structure. This means that Symbol does not come with yet another file format to configure your project; just keep using *.cm files for SML/NJ and *.mlb files for MLton.

Install

Installing Symbol globally is only required by the collaborators who initially set up new SML projects. The global command is called symbol-new and is used solely for scaffolding new projects. Once a Symbol project has been created, a script called symbol will exist locally within that project.

macOS

On macOS, you can use Homebrew:

brew install jez/formulae/symbol-new

From source

You can also install from source:

git clone https://github.com/jez/symbol
cd symbol
make install

This will install to ~/.local/bin/symbol-new. If you'd like to install to a different prefix, you can pass that to the make command. For example,

make install prefix=/usr/local

will instead install to /usr/local/bin/symbol-new.

Quickstart

Creating a new project

# Given `<target>` is the name to call the executable for your project:
symbol-new <target>

# or, to create a new project with minimal scaffolding:
symbol-new <target> --empty

# ^ This also works to initialize an existing project.

Builing a Symbol project

# Build the project (by default uses SML/NJ)
./symbol make

# Build the project with MLton (takes longer, but much faster executable)
./symbol make with=mlton

# Build the project (by default uses MLton), then install to ~/.local/bin
./symbol install

# same as above, but installs to /usr/local/bin
./symbol install prefix=/usr/local

Help

# Global
symbol-new --help

# Local
./symbol --help

Tips

These are some general tips for working with Symbol and Standard ML.

Project Structure

Symbol adds an initial project structure with a src/ folder. Feel free to arrange the SML source files however you want, and pull in whatever dependencies you want. However:

• There must always be either a <target>.cm or <target>.mlb in the same folder as the symbol script.

• The <target>.cm must make available a Main.main function.

  • This function is given directly to the ml-build command.
  • See the CM User Guide for more information.

• The choice for <target> cannot easily be changed after running symbol-new.

  • If you do want to change it, you'll have to manually edit the target variables in ./symbol and ./.symbol.mk

And then a suggestion: keep your <target>.cm and <target>.mlb files very transparent. Don't try to hide intermediate signatures, structures, or functors. This will make it easier to test your code.

If you intend your project to produce both an executable and a library, have a separate CM file that hides internal implementation details from downstream users of your library, and keep the one that exposes everything.

Your PATH

There are a few folders you might want to add or make sure are in your PATH. To add all of the below folders to your PATH, add these lines to your bashrc or zshrc:

export PATH="$PATH:.symbol-work/bin"
export PATH="$PATH:."
export PATH="$PATH:$HOME/.local/bin"

The folders themselves are:

• .symbol-work/bin

  If this folder is in your PATH, you can replace

  ❯ .symbol-work/bin/my-target
  

  with just

  ❯ my-target
  

• . (the current directory)

  If this folder is in your PATH, you can replace

  ❯ ./symbol make
  

  with just

  ❯ symbol make
  

• $HOME/.local/bin

  This is the place where ./symbol install puts executables by default. If this folder is not in your PATH, you can use prefix=... to specify a folder that is on your PATH. For example:

  ./symbol install prefix=/usr/local
  

Contributing

To learn about historical context and implementation decisions:

• Read DECISIONS.md

To set up your development environment:

# macOS:
brew bundle

# linux: install the packages listed in ./Brewfile

For developing on Symbol locally:

# To run the lint checks:
make lint

# To run the tests:
make test

# To re-record the snapshot tests:
make test update=1

To make a new test:

• Add a .sh file anywhere in tests/.
• Make it executable.

To make a new snapshot test:

• Make a new test, say tests/foo.sh
• Make an empty file like tests/foo.sh.exp
• Run make test update=1

To bump the version:

• Update the VERSION in symbol-new
• Update the version test output (version.sh.exp)
• Commit the change, and create a new git tag with that version
• Make a new release on GitHub (hub release)
• Update the Homebrew formula

License