Initial commit

Basic GNU standard files are added, and we now stop worrying about
monadic anamorphisms.

The current focus is on testing the correctness of the algorithm, so I
need convenient support for manipulating, interpreting, examining, and
per chance animating nondeterministic automata.

1 files changed, 27 insertions, 0 deletions

diff --git a/receme/src/catana.rs b/receme/src/catana.rs
new file mode 100644
index 0000000..e3d4728
--- /dev/null
+++ b/receme/src/catana.rs
@@ -0,0 +1,27 @@
+//! This file defines behaviours of catamorphisms and anamorphisms.
+//!
+//! A catamorphism collapses a recursive structure into a flat value,
+//! whereas an anamorphism expands a value into a recursive structure.
+
+use crate::{algebra::Algebra, coalgebra::Coalgebra, functor::Functor};
+
+/// A type that implements Cata is capable of being collapsed into a single value.
+///
+/// The catamorphism consumes `self`.
+pub trait Cata<T, F: Functor<T>, A: Algebra<T, F>> {
+    /// A catamorphism takes a recursive structure and an algebra for
+    /// the recursive structure, and returns a single, flat, collapsed
+    /// value.
+    fn cata(self, alg: A) -> T;
+}
+
+/// A type that implements Ana is capable of being expanded from a
+/// flat value.
+///
+/// The anamorphism consumes `self`.
+pub trait Ana<T, F: Functor<T>, C: Coalgebra<T, F>> {
+    /// An anamorphism takes a single, flat, collapsed value and a
+    /// co-algebra for a recursive structure, and returns that
+    /// recursive structure.
+    fn ana(value: T, coalg: C) -> Self;
+}