From a3ab765efe831505179a5966b5546509cb862717 Mon Sep 17 00:00:00 2001
From: Greg Brown <gmb60@cam.ac.uk>
Date: Sat, 16 Jan 2021 12:35:13 +0000
Subject: Fix warnings in `chomp::ast`.

---
 src/chomp/ast/error.rs | 34 ++++++++++++++++++++++++++++++++--
 src/chomp/ast/mod.rs   |  6 +++---
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/src/chomp/ast/error.rs b/src/chomp/ast/error.rs
index d2c49cd..7be5354 100644
--- a/src/chomp/ast/error.rs
+++ b/src/chomp/ast/error.rs
@@ -14,13 +14,43 @@ pub enum SubstituteError {
 
 impl From<SubstituteError> for syn::Error {
     fn from(e: SubstituteError) -> Self {
-        todo!()
+        match e {
+            SubstituteError::FreeParameter { span, .. } => {
+                Self::new(span.unwrap_or_else(Span::call_site), "unbound parameter")
+            }
+            SubstituteError::WrongArgCount { call, expected, span } => {
+                let msg = if call.args.len() == 1 {
+                    format!("this function takes {} arguments but 1 was supplied", expected)
+                } else {
+                    format!("this function takes {} arguments but {} were supplied", expected, call.args.len())
+                };
+
+                Self::new(span.unwrap_or_else(Span::call_site), msg)
+            }
+        }
     }
 }
 
 impl Display for SubstituteError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        todo!()
+        match self {
+            Self::FreeParameter { param, span, name } => {
+                let start = span.unwrap_or_else(Span::call_site).start();
+                if let Some(name) = name {
+                    write!(f, "{}:{}: unbound parameter `{}`", start.line, start.column, name)
+                } else {
+                    write!(f, "{}:{}: unbound parameter '{}", start.line, start.column, param.index)
+                }
+            }
+            Self::WrongArgCount { call, expected, span } => {
+                let start = span.unwrap_or_else(Span::call_site).start();
+                if call.args.len() == 1 {
+                    write!(f, "{}:{}: this function takes {} arguments but 1 was supplied", start.line, start.column, expected)
+                } else {
+                    write!(f, "{}:{}: this function takes {} arguments but {} were supplied", start.line, start.column, expected, call.args.len())
+                }
+            }
+        }
     }
 }
 
diff --git a/src/chomp/ast/mod.rs b/src/chomp/ast/mod.rs
index 110e5c0..9a159e4 100644
--- a/src/chomp/ast/mod.rs
+++ b/src/chomp/ast/mod.rs
@@ -8,7 +8,7 @@ use super::Name;
 pub mod error;
 pub mod substitute;
 
-#[derive(Clone, Debug, Default, Eq, PartialEq, Hash)]
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq, Hash)]
 pub struct Epsilon;
 
 pub type Literal = String;
@@ -102,7 +102,7 @@ impl PartialEq for Fix {
 
 impl Eq for Fix {}
 
-#[derive(Clone, Debug, Eq, Hash, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub struct Variable {
     pub index: usize,
 }
@@ -113,7 +113,7 @@ impl Display for Variable {
     }
 }
 
-#[derive(Clone, Debug, Eq, Hash, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub struct Parameter {
     pub index: usize,
 }
-- 
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