Add labelled expressions.

Restructure project (again).

Convert `Cat` and `Alt` from binary to n+2-ary.

1 files changed, 27 insertions, 0 deletions

diff --git a/src/chomp/ast/error.rs b/src/chomp/ast/error.rs
new file mode 100644
index 0000000..d2c49cd
--- /dev/null
+++ b/src/chomp/ast/error.rs
@@ -0,0 +1,27 @@
+use std::{error::Error, fmt::{self, Display}};
+
+use proc_macro2::Span;
+
+use crate::chomp::Name;
+
+use super::{Call, Parameter};
+
+#[derive(Debug)]
+pub enum SubstituteError {
+    FreeParameter { param: Parameter, span: Option<Span>, name: Option<Name> },
+    WrongArgCount { call: Call, expected: usize, span: Option<Span> },
+}
+
+impl From<SubstituteError> for syn::Error {
+    fn from(e: SubstituteError) -> Self {
+        todo!()
+    }
+}
+
+impl Display for SubstituteError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        todo!()
+    }
+}
+
+impl Error for SubstituteError {}