Add symbolic regression experiment.

offchain/src/bin/gp_spec_tester.rs

@@ -0,0 +1,36 @@
+use anyhow::Result;
+use rand::thread_rng;
+use rand::Rng;
+
+// Suppose you have these in your library:
+use offchain::gp::generate_spec::ranmdom_code_fixed;
+use offchain::gp::mutation::mutate_by_index;
+use offchain::compiler::ast::UntypedAst;
+
+fn main() -> Result<()> {
+    let mut rng = thread_rng();
+
+    // We'll produce, say, 3 random ASTs ("subjects").
+    let num_subjects = 3;
+    let max_points = 6;
+
+    for i in 0..num_subjects {
+        // Generate a random AST
+        let original = ranmdom_code_fixed(&mut rng, max_points);
+        println!("=== Subject #{} ===", i);
+        println!("Original AST:\n{:#?}", original);
+
+        // Let's do 2 successive mutations on it
+        let mut prev = original.clone();
+        for mut_idx in 0..2 {
+            let mutated = mutate_by_index(&prev, &mut rng, max_points);
+            println!("Mutation #{} result:\n{:#?}", mut_idx, mutated);
+            prev = mutated; // so the next iteration mutates from the last result
+        }
+
+        println!("=== End of Subject #{} ===\n", i);
+    }
+
+    println!("Done generating & mutating random ASTs!");
+    Ok(())
+}