repline: Promote to its own crate!

cl-repl: Major refactor based on the design of typeck.rs

repline/src/error.rs

@@ -0,0 +1,42 @@
+use crate::iter::chars::BadUnicode;
+
+/// Result type for Repline
+pub type ReplResult<T> = std::result::Result<T, Error>;
+/// Borrowed error (does not implement [Error](std::error::Error)!)
+#[derive(Debug)]
+pub enum Error {
+    /// User broke with Ctrl+C
+    CtrlC(String),
+    /// User broke with Ctrl+D
+    CtrlD(String),
+    /// Invalid unicode codepoint
+    BadUnicode(u32),
+    /// Error came from [std::io]
+    IoFailure(std::io::Error),
+    /// End of input
+    EndOfInput,
+}
+
+impl std::error::Error for Error {}
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Error::CtrlC(_) => write!(f, "Ctrl+C"),
+            Error::CtrlD(_) => write!(f, "Ctrl+D"),
+            Error::BadUnicode(u) => write!(f, "\\u{{{u:x}}} is not a valid unicode codepoint"),
+            Error::IoFailure(s) => write!(f, "{s}"),
+            Error::EndOfInput => write!(f, "End of input"),
+        }
+    }
+}
+impl From<std::io::Error> for Error {
+    fn from(value: std::io::Error) -> Self {
+        Self::IoFailure(value)
+    }
+}
+impl From<BadUnicode> for Error {
+    fn from(value: BadUnicode) -> Self {
+        let BadUnicode(code) = value;
+        Self::BadUnicode(code)
+    }
+}