From 8fed76307a88fd3276866cec330b350119d4484a Mon Sep 17 00:00:00 2001
From: Felix <felix@felixleitner.com>
Date: Tue, 23 Jan 2024 16:03:32 +0000
Subject: [PATCH 1/2] add missing import

---
 solvers/minion/src/lib.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/solvers/minion/src/lib.rs b/solvers/minion/src/lib.rs
index 835cda3c6..ffb2661aa 100644
--- a/solvers/minion/src/lib.rs
+++ b/solvers/minion/src/lib.rs
@@ -29,6 +29,7 @@
 //! use minion_rs::ast::*;
 //! use minion_rs::run_minion;
 //! use std::collections::HashMap;
+//! use std::sync::Mutex;
 //!
 //! // Get solutions out of Minion.
 //! // See the documentation for Callback for details.

From d61501829d8340c80b565d4ebd7f0d0cae2e6561 Mon Sep 17 00:00:00 2001
From: Felix <felix@felixleitner.com>
Date: Mon, 22 Jan 2024 14:53:33 +0000
Subject: [PATCH 2/2] Define rule struct and give example definition

Co-authored-by: Nik <nd60@st-andrews.ac.uk>
---
 conjure_oxide/src/lib.rs        |  1 +
 conjure_oxide/src/rules/mod.rs  | 11 ++++++++++
 crates/conjure_core/src/lib.rs  |  1 +
 crates/conjure_core/src/rule.rs | 36 +++++++++++++++++++++++++++++++++
 4 files changed, 49 insertions(+)
 create mode 100644 conjure_oxide/src/rules/mod.rs
 create mode 100644 crates/conjure_core/src/rule.rs

diff --git a/conjure_oxide/src/lib.rs b/conjure_oxide/src/lib.rs
index c2c17a283..e7f1a854a 100644
--- a/conjure_oxide/src/lib.rs
+++ b/conjure_oxide/src/lib.rs
@@ -1,6 +1,7 @@
 pub mod error;
 pub mod find_conjure;
 pub mod parse;
+pub mod rules;
 mod solvers;
 
 pub use conjure_core::ast; // re-export core::ast as conjure_oxide::ast
diff --git a/conjure_oxide/src/rules/mod.rs b/conjure_oxide/src/rules/mod.rs
new file mode 100644
index 000000000..3911c82ed
--- /dev/null
+++ b/conjure_oxide/src/rules/mod.rs
@@ -0,0 +1,11 @@
+use conjure_core::ast::Expression;
+use conjure_core::rule::{Rule, RuleApplicationError};
+
+fn identity(expr: &Expression) -> Result<Expression, RuleApplicationError> {
+    Ok(expr.clone())
+}
+
+pub static IDENTITY_RULE: Rule = Rule {
+    name: "identity",
+    application: identity,
+};
diff --git a/crates/conjure_core/src/lib.rs b/crates/conjure_core/src/lib.rs
index 6471a8b4f..df41804d3 100644
--- a/crates/conjure_core/src/lib.rs
+++ b/crates/conjure_core/src/lib.rs
@@ -1,4 +1,5 @@
 pub mod ast;
+pub mod rule;
 
 pub mod solvers;
 pub use solvers::Solver;
diff --git a/crates/conjure_core/src/rule.rs b/crates/conjure_core/src/rule.rs
new file mode 100644
index 000000000..059e738a9
--- /dev/null
+++ b/crates/conjure_core/src/rule.rs
@@ -0,0 +1,36 @@
+use std::fmt::{self, Display, Formatter};
+
+use thiserror::Error;
+
+use crate::ast::Expression;
+
+#[derive(Debug, Error)]
+pub enum RuleApplicationError {
+    #[error("Rule is not applicable")]
+    RuleNotApplicable,
+}
+
+#[derive(Clone, Debug)]
+pub struct Rule<'a> {
+    pub name: &'a str,
+    pub application: fn(&Expression) -> Result<Expression, RuleApplicationError>,
+}
+
+impl<'a> Rule<'a> {
+    pub fn new(
+        name: &'a str,
+        application: fn(&Expression) -> Result<Expression, RuleApplicationError>,
+    ) -> Self {
+        Self { name, application }
+    }
+
+    pub fn apply(&self, expr: &Expression) -> Result<Expression, RuleApplicationError> {
+        (self.application)(expr)
+    }
+}
+
+impl<'a> Display for Rule<'a> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.name)
+    }
+}