Export crate::error::Error and derive Error for it

src/error.rs

@@ -1,4 +1,4 @@
-use std::fmt;
+use std::{error::Error as StdError, fmt};
 
 #[derive(Debug)]
 pub enum Error {
@@ -32,6 +32,8 @@ pub enum Error {
     ExpectBinOpToken,
 }
 
+impl StdError for Error {}
+
 #[cfg(not(tarpaulin_include))]
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

src/lib.rs

@@ -169,6 +169,7 @@ fn init() {
 pub type Value = value::Value;
 pub type Context = context::Context;
 pub type Result<T> = define::Result<T>;
+pub type Error = error::Error;
 pub type ExprAST<'a> = parser::ExprAST<'a>;
 pub type InfixOpType = operator::InfixOpType;
 pub type InfixOpAssociativity = operator::InfixOpAssociativity;