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!(),
+    }
+}