anchor.diff:          phi
   
         phi
  -    | For (var, start, finish, step, body) ->
  +    | For (varName, start, finish, step, body) ->
         // Output this as:
         //   ...
         //   start = startexpr
  
positive.code:     | Minus
      | LessThan
      | Multiply
  
      member op.Code =
        match op with
  
negative.code:       let parseAssign =
          let parseAssignBody = parseEqual .>> parseWhiteSpace >>. parseExpr
          pipe2 parseIdentifier parseAssignBody (fun var expr -> (var, expr))
         
        let parseAssignExpr = parseVar >>. parseAssign |>> (fun (var,  expr) -> Assign (Variable var, expr))
  
        let parseCall =
          let parseArgs =
  