1 files changed, 52 insertions, 0 deletions
diff --git a/src/chomp/ast-old/error.rs b/src/chomp/ast-old/error.rs
new file mode 100644
index 0000000..9057ec3
--- /dev/null
+++ b/src/chomp/ast-old/error.rs
@@ -0,0 +1,52 @@
+use super::{Expression, Lambda, NamedExpression};
+use proc_macro2::Span;
+use std::{
+    error::Error,
+    fmt::{self, Display},
+};
+
+#[derive(Debug)]
+pub enum TranslateError {
+    CallNotAFunction {
+        on: Expression,
+        span: Option<Span>,
+    },
+    WrongArgCount {
+        lambda: Lambda,
+        args: Vec<NamedExpression>,
+        span: Option<Span>,
+    },
+}
+
+impl From<TranslateError> for syn::Error {
+    fn from(e: TranslateError) -> Self {
+        let msg = e.to_string();
+        let span = match e {
+            TranslateError::CallNotAFunction { span, .. }
+            | TranslateError::WrongArgCount { span, .. } => span,
+        };
+
+        Self::new(span.unwrap_or_else(Span::call_site), msg)
+    }
+}
+
+impl Display for TranslateError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::CallNotAFunction { .. } => {
+                write!(f, "call expected a function")
+            }
+            Self::WrongArgCount { lambda, args, .. } => match (lambda.args.len(), args.len()) {
+                (1, n) => write!(f, "this function takes 1 argument but {} were supplied", n),
+                (m, _) => write!(f, "this function takes {} arguments but 1 was supplied", m),
+                (m, n) => write!(
+                    f,
+                    "this function takes {} arguments but {} were supplied",
+                    m, n
+                ),
+            },
+        }
+    }
+}
+
+impl Error for TranslateError {}