Add map functions for Error<> and Info<> ranges. (Marwes#86)

It's possible to `map_err_range` for `ParseResult<>` too, but it's
awkward because the output type needs to be a compatible `StreamOnce`.
As suggested in
Marwes#86 (comment),
it's probably best to either change the parse result type entirely, or
wait for rust-lang/rust#21903.

This at least helps consumers convert `ParseError<>` into something
that can implement `std::fmt::Display`.

src/primitives.rs

@@ -56,6 +56,18 @@ pub enum Info<T, R> {
  Borrowed(&'static str),
 }
 
+impl<T, R> Info<T, R> {
+ pub fn map_range<F, S>(self, f: F) -> Info<T, S> where F: FnOnce(R) -> S {
+ use self::Info::*;
+ match self {
+ Token(t) => Token(t),
+ Range(r) => Range(f(r)),
+ Owned(s) => Owned(s),
+ Borrowed(x) => Borrowed(x),
+ }
+ }
+}
+
 impl<T: PartialEq, R: PartialEq> PartialEq for Info<T, R> {
  fn eq(&self, other: &Info<T, R>) -> bool {
  match (self, other) {
@@ -110,6 +122,18 @@ pub enum Error<T, R> {
  Other(Box<StdError + Send + Sync>),
 }
 
+impl<T, R> Error<T, R> {
+ pub fn map_err_range<F, S>(self, f: F) -> Error<T, S> where F: FnOnce(R) -> S {
+ use self::Error::*;
+ match self {
+ Unexpected(x) => Unexpected(x.map_range(f)),
+ Expected(x) => Expected(x.map_range(f)),
+ Message(x) => Message(x.map_range(f)),
+ Other(x) => Other(x),
+ }
+ }
+}
+
 impl<T: PartialEq, R: PartialEq> PartialEq for Error<T, R> {
  fn eq(&self, other: &Error<T, R>) -> bool {
  match (self, other) {