Cavalry

Cavalry is a mini programming language of my own design where written programs can be "verified", i.e. the implementation of the program can be rigorously checked against its logical specification for correctness, without ever running the code.

Details about Cavalry and Hoare logic are in an article on my website here.

Requirements

• OCaml >= 4.08 and opam
• Why3 with the Alt-Ergo 2.4.3 SMT solver, used to discharge verification proof obligations

Running

git clone git@github.com:benmandrew/cavalry.git
cd cavalry
opam install --deps-only --with-test .
why3 config detect  # let Why3 find the Alt-Ergo prover
dune build
# Verify [example.cav]
dune exec -- cav verify example.cav
# Run [example.cav]
dune exec -- cav run example.cav

Testing

dune runtest

Example programs

Computing triangle numbers

{ x = 0 && i = 0 }
while i < 10 do
  { 2 * x = (i * (i - 1)) }
  x <- x + i;
  i <- i + 1
end;
x
{ x = 45 }

Euclidean division procedure

procedure euclidean_div () =
  requires { x >= 0 }
  ensures { x = q * y + r && 0 <= r && r < y }
  writes { q, r }
  q <- 0;
  r <- x;
  while r >= y do
    { x = q * y + r && 0 <= r }
    r <- r - y;
    q <- q + 1
  end
end

{ true }
x <- 42;
y <- 17;
q <- 0;
r <- 0;
euclidean_div()
{ q = 2 && r = 8 }