1 files changed, 43 insertions, 2 deletions
diff --git a/rust/src/ast.rs b/rust/src/ast.rs
index dfb6862..3f8b772 100644
--- a/rust/src/ast.rs
+++ b/rust/src/ast.rs
@@ -1,6 +1,9 @@
-use std::fmt::{self, Display};
-
+use proptest::{
+    prelude::*,
+    string::{string_regex, RegexGeneratorStrategy},
+};
 use serde::{Deserialize, Serialize};
+use std::fmt::{self, Display};
 
 #[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
 pub enum Value {
@@ -26,3 +29,41 @@ impl Display for Value {
         }
     }
 }
+
+use Value::*;
+
+pub const IDENTIFIER: &str = "\\pL(\\pL|\\pN)*";
+
+pub fn identifier() -> RegexGeneratorStrategy<String> {
+    string_regex(IDENTIFIER).unwrap()
+}
+
+impl Arbitrary for Value {
+    type Parameters = ();
+    type Strategy = BoxedStrategy<Self>;
+
+    fn arbitrary_with(_args: ()) -> Self::Strategy {
+        let any_num = any::<i32>().prop_map(Num);
+        let any_bool = any::<bool>().prop_map(Bool);
+        let leaf = prop_oneof![
+            any_num,
+            any_bool,
+            // see https://unicode.org/reports/tr18/#General_Category_Property for one letter unicode categories
+            identifier().prop_map(Sym),
+        ];
+        let expr = leaf.prop_recursive(4, 128, 5, move |inner| {
+            prop_oneof![
+                (inner.clone(), inner.clone()).prop_map(|(l, r)| App(Box::new(l), Box::new(r))),
+                (identifier(), inner.clone()).prop_map(|(var, body)| Lam(var, Box::new(body))),
+                (identifier(), inner.clone(), inner.clone()).prop_map(|(var, body, expr)| {
+                    Value::Let(var, Box::new(body), Box::new(expr))
+                }),
+            ]
+        });
+        prop_oneof![
+            expr.clone(),
+            (identifier(), expr).prop_map(|(var, body)| Def(var, Box::new(body)))
+        ]
+        .boxed()
+    }
+}