Simple yecc and leex parser

guardian_lexer.xrl

Definitions.

WS  = ([\000-\s]|%.*)
T_VAR   = [A-Za-z\.\-]

Rules.
or                :   {token,{'T_OR',TokenLine,list_to_atom(TokenChars)}}.
and               :   {token,{'T_AND',TokenLine,list_to_atom(TokenChars)}}.
{T_VAR}+          :   {token,{'T_VAR',TokenLine,TokenChars}}.
[()]              :   {token,{list_to_atom(TokenChars),TokenLine}}.
{WS}+             :   skip_token.

Erlang code.

guardian_parser.yrl

Nonterminals
V.

Terminals '(' ')' T_VAR T_AND T_OR.

Rootsymbol V.

V -> V T_AND V : {'$2', '$1', '$3'}.
V -> V T_OR V : {'$2', '$1', '$3'}.
V -> '(' V ')' : '$2'.
V -> T_VAR : '$1'.

parser.exs

def expr({:T_VAR, line, name}, props) do
  # failsafe
  Map.get(props, name) || false
end

def expr({op, left, right}, props) do
  case op do
    {:T_AND, line, _} -> expr(left, props) and expr(right, props)
    {:T_OR, line, _} -> expr(left, props) or expr(right, props)
    _ -> raise "CO-CO-COMBO BREAKER"
  end
end

def parse(expression, props) do
  {:ok, tokens, _} = :guardian_lexer.string(expression)
  {:ok, tree} = :guardian_parser.parse(tokens)
  expr(tree, props)
end

parse('fail or DOMINATE.WORLD or (view.users and delete.users) or root', %{
  'view.users' => false,
  'DOMINATE.WORLD' => false,
  'delete.users' => false,
  'root' => true
})  |> IO.inspect