anchor.diff:  
         let parseVariable = parseIdentifier |>> Variable
   
  +      let parseAssign =
  +        let parseAssignBody = parseEqual .>> parseWhiteSpace >>. parseExpr
  +        pipe2 parseIdentifier parseAssignBody (fun var expr -> (var, expr))
  +
         let parseCall =
           let parseArgs =
             let parseExprs = sepBy parseExpr parseComma
  
positive.code:     | Variable of Name: string
      (* variant for function calls. *)
      | Call of (string * seq<Expr>)
  
      override expr.ToString() =
        match expr with
  
negative.code:   let parseComma = pstring Comma .>> parseWhiteSpace
    let isSymbolicOperatorChar = isAnyOf SpecialCharacters
  
    let remainingOperatorCharsAndWhiteSpace = manySatisfy isSymbolicOperatorChar .>> parseWhiteSpace
  
    let parseWhiteSpace1 = spaces1
  