From 1a43c2d1a5c76fa05c163c0c7bfceb8523e74e06 Mon Sep 17 00:00:00 2001
From: VegOwOtenks <vegowotenks@jossco.de>
Date: Fri, 2 May 2025 19:38:30 +0200
Subject: [PATCH] trait definition and struct-tuple example

---
 .gitignore       |  1 +
 Cargo.lock       |  7 +++++++
 Cargo.toml       |  6 ++++++
 src/example.rs   | 28 ++++++++++++++++++++++++++++
 src/generic.rs   | 31 +++++++++++++++++++++++++++++++
 src/instances.rs | 21 +++++++++++++++++++++
 src/lib.rs       | 18 ++++++++++++++++++
 7 files changed, 112 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.lock
 create mode 100644 Cargo.toml
 create mode 100644 src/example.rs
 create mode 100644 src/generic.rs
 create mode 100644 src/instances.rs
 create mode 100644 src/lib.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..b69769b
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "generic"
+version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..c1c4ae5
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "generic"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/src/example.rs b/src/example.rs
new file mode 100644
index 0000000..8b92e11
--- /dev/null
+++ b/src/example.rs
@@ -0,0 +1,28 @@
+use crate::generic::{Field, Sum, Generic};
+
+
+struct IntPair {
+    a: i32,
+    b: i32
+}
+
+impl Generic for IntPair {
+    type Representation = Sum<Field<i32>, Field<i32>>;
+    fn generalize(self) -> Self::Representation {
+        Sum { 
+            left: Field { value: self.a },
+            right: Field { value: self.b }
+        }
+    }
+    fn specialize(rep: Self::Representation) -> Self {
+        let Sum {
+            left: Field { value: a },
+            right: Field { value: b },
+        } = rep;
+        IntPair { a, b }
+    }
+}
+
+fn convert(x: IntPair) -> (i32, i32) {
+    Generic::specialize(x.generalize())
+}
diff --git a/src/generic.rs b/src/generic.rs
new file mode 100644
index 0000000..c12c299
--- /dev/null
+++ b/src/generic.rs
@@ -0,0 +1,31 @@
+pub struct Sum<Con, Rhs> where Con: IsConType, Rhs: IsRepType {
+    pub left: Con,
+    pub right: Rhs,
+}
+
+pub struct Product<T, Rhs> where Rhs: IsConType {
+    pub left: Field<T>,
+    pub right: Rhs
+}
+
+pub struct Field<T> {
+    pub value: T
+}
+
+// types used for generic representation
+pub trait IsRepType {}
+impl<Lhs: IsConType, Rhs: IsRepType> IsRepType for Sum<Lhs, Rhs> {}
+impl<T: IsRepType, Rhs: IsConType> IsRepType for Product<T, Rhs> {}
+impl<T> IsRepType for Field<T> {}
+
+// types that represent constructors
+pub trait IsConType {}
+impl<T, Rhs: IsConType> IsConType for Product<T, Rhs> {}
+impl<T> IsConType for Field<T> {}
+
+
+pub trait Generic {
+    type Representation: IsRepType;
+    fn generalize(self) -> Self::Representation;
+    fn specialize(rep: Self::Representation) -> Self;
+}
diff --git a/src/instances.rs b/src/instances.rs
new file mode 100644
index 0000000..f470fd1
--- /dev/null
+++ b/src/instances.rs
@@ -0,0 +1,21 @@
+use crate::generic::{Field, Generic, Sum};
+
+impl<A, B> Generic for (A, B) {
+    type Representation = Sum<Field<A>, Field<B>>;
+
+    fn generalize(self) -> Self::Representation {
+        let (l, r) = self;
+        Sum {
+            left: Field { value: l },
+            right: Field { value: r }
+        }
+    }
+
+    fn specialize(rep: Self::Representation) -> Self {
+        let Sum {
+            left: Field { value: a },
+            right: Field { value: b },
+        } = rep;
+        (a, b)
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..dc859d7
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,18 @@
+pub mod generic;
+mod example;
+pub mod instances;
+
+pub fn add(left: u64, right: u64) -> u64 {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}