Add more local mutation

offchain/src/gp/generate_spec.rs

@@ -47,7 +47,7 @@ impl InstructionSet {
             InstructionAtom::Opcode(op) => UntypedAst::Instruction(op.clone()),
             InstructionAtom::EphemeralInt => {
                 // For ephemeral int, produce a random literal in some range
-                let val = rng.gen_range(-100..100);
+                let val = rng.gen_range(-30..30);
                 UntypedAst::IntLiteral(val)
             }
         }

offchain/src/gp/local_mutation.rs

@@ -0,0 +1,114 @@
+//! src/gp/local_mutation.rs
+//! A localized mutation operator that makes small tweaks depending on node type.
+
+use rand::Rng;
+use crate::compiler::ast::{UntypedAst, OpCode};
+use crate::gp::mutation::{
+    enum_nodes_dfs, get_subtree, replace_subtree,
+};
+use crate::gp::generate_spec::{
+    InstructionAtom, InstructionSet,
+};
+
+/// A top-level function to perform a localized mutation with a chosen `InstructionSet`.
+pub fn local_mutation(
+    original: &UntypedAst,
+    rng: &mut impl Rng,
+    instr_set: &InstructionSet,
+) -> UntypedAst {
+    let all_paths = enum_nodes_dfs(original);
+    let idx = rng.gen_range(0..all_paths.len());
+    let chosen_path = &all_paths[idx];
+
+    let old_subtree = get_subtree(original, chosen_path);
+    let new_subtree = local_mutation_node(&old_subtree, rng, instr_set);
+    replace_subtree(original, chosen_path, new_subtree)
+}
+
+/// A convenience wrapper that always uses `InstructionSet::new_default()`.
+pub fn local_mutation_fixed(
+    original: &UntypedAst,
+    rng: &mut impl Rng,
+) -> UntypedAst {
+    let instr_set = InstructionSet::new_default();
+    local_mutation(original, rng, &instr_set)
+}
+
+fn local_mutation_node(
+    subtree: &UntypedAst,
+    rng: &mut impl Rng,
+    instr_set: &InstructionSet,
+) -> UntypedAst {
+    match subtree {
+        UntypedAst::IntLiteral(val) => {
+            let delta = rng.gen_range(-5..=5);
+            let new_val = val.saturating_add(delta);
+            UntypedAst::IntLiteral(new_val)
+        }
+        UntypedAst::Instruction(op) => {
+            let mut new_op = pick_random_opcode(rng, instr_set);
+            for _ in 0..3 {
+                if &new_op != op {
+                    break;
+                }
+                new_op = pick_random_opcode(rng, instr_set);
+            }
+            UntypedAst::Instruction(new_op)
+        }
+        UntypedAst::Sublist(children) => {
+            let choice = rng.gen_range(0..3);
+            let mut new_children = children.clone();
+
+            match choice {
+                0 => {
+                    // remove one child if possible
+                    if !new_children.is_empty() {
+                        let i = rng.gen_range(0..new_children.len());
+                        new_children.remove(i);
+                    }
+                }
+                1 => {
+                    // insert a new small node
+                    let i = rng.gen_range(0..=new_children.len());
+                    let node = create_small_node(rng, instr_set);
+                    new_children.insert(i, node);
+                }
+                2 => {
+                    // reorder two children
+                    if new_children.len() > 1 {
+                        let i = rng.gen_range(0..new_children.len());
+                        let j = rng.gen_range(0..new_children.len());
+                        new_children.swap(i, j);
+                    }
+                }
+                _ => {}
+            }
+
+            UntypedAst::Sublist(new_children)
+        }
+    }
+}
+
+fn pick_random_opcode(rng: &mut impl Rng, instr_set: &InstructionSet) -> OpCode {
+    use crate::compiler::ast::OpCode;
+
+    let mut opcode_list: Vec<&OpCode> = Vec::new();
+    for atom in &instr_set.atoms {
+        if let InstructionAtom::Opcode(ref op) = atom {
+            opcode_list.push(op);
+        }
+    }
+    if opcode_list.is_empty() {
+        // fallback => default to Noop
+        return OpCode::Noop;
+    }
+    let i = rng.gen_range(0..opcode_list.len());
+    opcode_list[i].clone()
+}
+
+fn create_small_node(
+    rng: &mut impl Rng,
+    instr_set: &InstructionSet,
+) -> UntypedAst {
+    instr_set.random_atom_as_ast(rng)
+}

offchain/src/gp/mod.rs

@@ -3,3 +3,4 @@ pub mod genetic_ops;
 pub mod generate;
 pub mod generate_spec;
 pub mod mutation;
+pub mod local_mutation;