Add support for recoverable syntax errors

1 files changed, 24 insertions, 1 deletions

diff --git a/src/state.rs b/src/state.rs
index 3294a2f..e8bd17a 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -2,10 +2,15 @@
 
 use crate::construct;
 use crate::tokenizer::Tokenizer;
+use alloc::string::{String, ToString};
 
 /// Result of a state.
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum State {
+    /// Syntax error.
+    ///
+    /// Only used by MDX.
+    Error(String),
     /// Move to [`Name`][] next.
     Next(Name),
     /// Retry in [`Name`][].
@@ -16,6 +21,24 @@ pub enum State {
     Nok,
 }
 
+impl State {
+    /// Turn a final state into a result.
+    ///
+    /// This doesn’t work on future states ([`State::Next`], [`State::Retry`]),
+    /// or on an attempt ([`State::Nok`]).
+    ///
+    /// But it turns the final result into an error if crashed.
+    pub fn to_result(&self) -> Result<(), String> {
+        match self {
+            State::Nok | State::Next(_) | State::Retry(_) => {
+                unreachable!("cannot turn intermediate state into result")
+            }
+            State::Ok => Ok(()),
+            State::Error(x) => Err(x.to_string()),
+        }
+    }
+}
+
 /// Names of states to move to.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 #[allow(clippy::enum_variant_names)]