Add random program generation and mutation.

offchain/src/gp/generate.rs

@@ -0,0 +1,79 @@
+use rand::Rng;
+use crate::compiler::ast::{UntypedAst, OpCode};
+
+pub fn random_sublist_ast(rng: &mut impl Rng, max_depth: usize) -> UntypedAst {
+    // 1) Choose how many children the top-level `Sublist` will have.
+    let len = rng.gen_range(1..=3);
+
+    // 2) Build a vector of sub-ASTs by calling `random_ast` for each child
+    let mut children = Vec::with_capacity(len);
+    for _ in 0..len {
+        // We start at `depth=1` because the top-level sublist itself is `depth=0`.
+        children.push(random_ast(rng, 1, max_depth));
+    }
+
+    // 3) Return a `Sublist` as the root node
+    UntypedAst::Sublist(children)
+}
+
+/// Generate a random `UntypedAst` by recursively building sub-trees, 
+/// int literals, or instructions. 
+///
+/// - `depth` tracks how deep we are in the tree.
+/// - `max_depth` is the maximum allowed depth to prevent infinite recursion.
+pub fn random_ast(rng: &mut impl Rng, depth: usize, max_depth: usize) -> UntypedAst {
+    if depth >= max_depth {
+        // Return something "terminal," 
+        // e.g. an IntLiteral or a single Instruction
+        random_terminal(rng)
+    } else {
+        // Weighted choice: 
+        // 0 => IntLiteral, 
+        // 1 => single Instruction,
+        // 2 => Sublist with children
+        let choice = rng.gen_range(0..3);
+        match choice {
+            0 => UntypedAst::IntLiteral(rng.gen_range(-10..10)),
+            1 => UntypedAst::Instruction(random_opcode(rng)),
+            2 => {
+                // Make a sublist with 1..=3 children
+                let len = rng.gen_range(1..=3);
+                let mut children = Vec::with_capacity(len);
+                for _ in 0..len {
+                    children.push(random_ast(rng, depth + 1, max_depth));
+                }
+                UntypedAst::Sublist(children)
+            }
+            _ => unreachable!(),
+        }
+    }
+}
+
+/// Generate a random "terminal" node. 
+/// Typically either an int literal or a single instruction.
+fn random_terminal(rng: &mut impl Rng) -> UntypedAst {
+    // Weighted choice:
+    // 0 => IntLiteral
+    // 1 => single Instruction
+    let choice = rng.gen_range(0..2);
+    match choice {
+        0 => UntypedAst::IntLiteral(rng.gen_range(-10..10)),
+        1 => UntypedAst::Instruction(random_opcode(rng)),
+        _ => unreachable!(),
+    }
+}
+
+/// Generate a random `OpCode` from your known set of instructions.
+pub fn random_opcode(rng: &mut impl Rng) -> OpCode {
+    let choice = rng.gen_range(0..6); 
+    // because we have 6 variants: Noop, Plus, Minus, Mult, Dup, Pop
+    match choice {
+        0 => OpCode::Noop,
+        1 => OpCode::Plus,
+        2 => OpCode::Minus,
+        3 => OpCode::Mult,
+        4 => OpCode::Dup,
+        5 => OpCode::Pop,
+        _ => unreachable!(),
+    }
+}

offchain/src/gp/genetic_ops.rs

@@ -1,10 +1,64 @@
-// use crate::compiler::ast::{Expr};
+use rand::Rng;
+use crate::compiler::ast::{UntypedAst, OpCode};
+use crate::gp::generate::{random_ast, random_opcode};
 
-// pub fn crossover(a: &Expr, b: &Expr) -> (Expr, Expr) {
-//     // stub
-//     (a.clone(), b.clone())
-// }
+/// Returns a new `UntypedAst` that is a mutated version of `original`.
+/// We do not modify `original`; we clone or build new pieces as needed.
+/// 
+/// - `depth`: current depth of this node,
+/// - `max_depth`: max allowed depth (to prevent infinite recursion).
+pub fn mutated_ast(original: &UntypedAst, rng: &mut impl Rng, depth: usize, max_depth: usize) -> UntypedAst {
+    // 10% chance: completely replace this node with a fresh random subtree
+    if rng.gen_range(0..100) < 10 {
+        return random_ast(rng, depth, max_depth);
+    }
 
-// pub fn mutate(expr: &mut Expr) {
-//     // stub
-// }
+    match original {
+        UntypedAst::IntLiteral(val) => {
+            // Another small chance to replace the entire node with random subtree
+            if rng.gen_range(0..100) < 10 {
+                return random_ast(rng, depth, max_depth);
+            }
+
+            // Otherwise, "tweak" the int by a small offset
+            let delta = rng.gen_range(-2..=2);
+            let new_val = val.saturating_add(delta);
+            UntypedAst::IntLiteral(new_val)
+        }
+        UntypedAst::Instruction(op) => {
+            // 10% chance to replace node
+            if rng.gen_range(0..100) < 10 {
+                return random_ast(rng, depth, max_depth);
+            }
+
+            // 50% chance to pick a new opcode
+            // or else keep the same
+            if rng.gen_bool(0.5) {
+                UntypedAst::Instruction(random_opcode(rng))
+            } else {
+                // Just clone the original
+                UntypedAst::Instruction(op.clone())
+            }
+        }
+        UntypedAst::Sublist(children) => {
+            // 10% chance to replace this sublist entirely
+            if rng.gen_range(0..100) < 10 {
+                return random_ast(rng, depth, max_depth);
+            }
+
+            // Otherwise, mutate zero or more children
+            let mut new_children = children.clone();
+            if !new_children.is_empty() {
+                // Choose how many kids to mutate: 
+                // e.g., 1..=min(2, children.len())
+                let mut_count = rng.gen_range(1..=new_children.len().min(2));
+
+                for _ in 0..mut_count {
+                    let idx = rng.gen_range(0..new_children.len());
+                    new_children[idx] = mutated_ast(&new_children[idx], rng, depth+1, max_depth);
+                }
+            }
+            UntypedAst::Sublist(new_children)
+        }
+    }
+}

offchain/src/gp/mod.rs

@@ -1,13 +1,3 @@
 pub mod population;
 pub mod genetic_ops;
-// pub mod fitness;
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_dummy() {
-        assert_eq!(2+2, 4);
-    }
-}
+pub mod generate;