Typed ERLC

The Problem

I have a dream, that one day there will be an Erlang compiler, which will generate high quality type-correct code from deduced value usages and -type and -specs. It will be able to print reasonable error messages about why the code is broken and will suggest how to fix the errors.

The current standard compiler, lib/compiler in OTP, and the type checking tool, Dialyzer in lib/dialyzer, are two separate projects:

• The compiler processes programs one file at a time, and never does it look at the rest of the program. This is nice when you compile one module to drop a .beam file into a running program and have them work together. The majority of Erlang projects are built together, from the project root, as single collection of sources. They are packaged together as a single unit and all modules run together.
• On the contrary, Dialyzer is what the compiler should be, it loads every file in the project together, and processes everything as a single program, checking all possible type usages and finding the type-related problems with high precision. Dialyzer does not compile Erlang code.

The typed_erlc Project

NOTE: This is an early stage work-in-progress.

This project is an alternate Erlang compiler, a fusion of OTP's lib/compiler and lib/dialyzer designed to load, analyze and compile all .erl files in your project together as a single unit, and perform live type deduction and type checking following the standard Erlang -spec() and -type() syntax.

Project File erlproject.toml

NOTE: The file format may and will change.

To perform the task, the tool needs to know all input files before the work begins. Hence the project file syntax is introduced (experimental). The default name for the project file is erlproject.toml, and the contents may look like:

[compiler_options]
include_paths = []          # default []

[inputs]
files = ["*.erl"]           # default ["*.erl"]
directories = ["src"]       # default ["."]
exclude_files = []          # TODO: not implemented; default []
exclude_directories = []    # TODO: not implemented; default []

You can use ** to match any portion of the path.

An empty erlproject.toml, is acceptable, consisting of comments, or no bytes at all. In this case entire current directory will be scanned for "*.erl" files, with all nested subdirectories.

Project Progress

NOTE: This is an early stage work-in-progress. The task list grows.

• Project configuration
• Preprocessor
  • Parse and interpret -define/-if*/-else/-endif directives by removing chunks of guarded code
  • Parse -include/include_lib directives
  • Perform inclusion
  • Parse and interpret -if(COND)
  • Substitute ?MACRO
  • Parse and interpret macros with arguments -define(MACRO(X, Y), ...)
• Erlang syntax parser
  • Common keywords and constructs
  • Module attributes
  • Binary syntax
  • Scientific float syntax
  • Maps syntax
  • Records syntax
  • Typespec syntax
• Type system and type inference engine
  • Define types, union types, special (any, none, ...)
  • Define expressions AST
  • Add support for types in the AST
  • Infer expression types
• ???
• Code generator