pub fn s(&self) -> Result<String, SexpError> {
        match *self {
            Sexp::String(ref s) => Ok(s.clone()),
            _ => Err(format!("not a string: {}", self).into()),
        }
    }
/// access the symbolic-expression as if it is a `String`
access the symbolic-expression as if it is a `String`
access the symbolic - expression as if it is a ` String `
pub fn s(&self) -> Result<String, SexpError> {
        match *self {
            Sexp::String(ref s) => Ok(s.clone()),
            _ => Err(format!("not a string: {}", self).into()),
        }
    }
pub fn s ( & self ) -> Result < String , SexpError > { match * self { Sexp :: String ( ref s ) => Ok ( s . clone ( ) ) , _ => Err ( format ! ( " " self ) . into ( ) ) , } }
access the symbolic-expression as if it is a `String`
access the symbolic - expression as if it is a ` String `
&self