lambda-ish PEG

gistfile1.txt

/*
 * Classic example grammar, which recognizes simple arithmetic expressions like
 * "2*(3+4)". The parser generated from this grammar then computes their value.
 */

start
  = expr:expression { return expr({}); }

expression
  = function
  / additive

function
  = "(" lambda:lambda ")(" expr:expression ")"
  {
    return function(env){ return lambda(env,expr()); };
  }

lambda
  = n:name "->" expr:expression
  {
    return function(env,val) {
      var env2 = {};
      for(var x in env){ env2[x] = env[x]; }
      env2[n.n] = val;
      return expr(env2);
    }
  }

additive
  = left:multiplicative "+" right:additive { return function(env){ return left(env)+right(env);} }
  / multiplicative

multiplicative
  = left:primary "*" right:multiplicative { return function(env){ return left(env)*right(env);}  }
  / primary

primary
  = integer
  / name
  / "(" additive:additive ")" { return additive; }

integer "integer"
  = digits:[0-9]+ 
  { 
    var n = parseInt(digits.join(""), 10); 
    return function(){ return n; }
  }

name
  = chars:([a-zA-Z][a-zA-Z0-9]*)
  { 
    var n = chars.join('');
    var f = function(env) { 
      if(n in env)
        return env[n];
      else
        return NaN;
    }
    f.n = n;
    return f;
  }