feat: Add default CompiledProgram

We can use the empty program as initializer for fields that store
CompiledProgram, such as in the web IDE.

src/ast.rs

@@ -20,7 +20,7 @@ use crate::value::{UIntValue, Value};
 use crate::{impl_eq_hash, parse};
 
 /// Map of witness names to their expected type, as declared in the program.
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, PartialEq, Default)]
 pub struct DeclaredWitnesses(HashMap<WitnessName, ResolvedType>);
 
 impl DeclaredWitnesses {

src/lib.rs

@@ -39,6 +39,17 @@ pub struct CompiledProgram {
     debug_symbols: DebugSymbols,
 }
 
+impl Default for CompiledProgram {
+    fn default() -> Self {
+        use simplicity::node::CoreConstructible;
+        Self {
+            simplicity: ProgNode::unit(&simplicity::types::Context::new()),
+            witness_types: DeclaredWitnesses::default(),
+            debug_symbols: DebugSymbols::default(),
+        }
+    }
+}
+
 impl CompiledProgram {
     /// Parse and compile a Simfony program from the given string.
     ///