README.md

Snake

Toy compiler and runtime from the Compilers class at Northeastern, targeting x86. Supports:

• Primitives:
  • Ints
  • Bools
• Heap-allocated structures:
  • Tuples (homogenous and heterogenous)
  • First-class lambda functions (with free-variable capture)
• Simple unary operators:
  • print to display values
  • add1 and sub1 on ints
  • ! (not) on bools
  • isnum, isbool, and istuple
• Simple binary operators:
  • == on all types (reference equality on tuples and lambdas)
  • +, -, *, <, >, <=, and => on ints
  • && and || on bools
• Tuple getters and setters:
  • Expression-as-key for homogenous tuples
  • Constant-as-key for heterogenous tuples
• Conditional branching with if-else
• Local variable bindings with let (lexical scope)
• Simple typechecking, with Hindley-Milner type inference and support for explicit annotations
• Tail-call elimination
• Recursive and mutually-recursive lambda definitions
• Semispace gargage collection using Cheney's algorithm
• Simple optimizations:
  • Constant folding
  • Common subexpression elimination
  • Dead assignment elimination

See test.ml for examples, along with examples of error-flagging.

Setting up

First get required tools. On OSX:

$ brew install nasm ocaml opam
$ opam init
$ opam install batteries extlib ounit

Then build and run the regression suite, to be sure everything works:

$ make test && ./test

NOTE: A number of tests will be auto-skipped on OS X. They depend on Valgrind, which still doesn't seem to work properly on Macs. Everything should work on Ubuntu (provided valgrind is installed).

Running

# Write a program:
$ cat <<EOF > input/my-program.snake
let fact = (lambda n:
    let rec tail_fact = (lambda m, acc:
      if (m == 0): acc
      else: tail_fact(m - 1, m * acc)) in
    tail_fact(n, 1)) in
  fact(10)
EOF
# Compile the program:
$ make output/my-program.run
# Run the program:
$ ./output/my-program.run