Add array.filter

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * Decode logs returned by `Transaction.getReceipt()` when available in ABI
 * Add support for array concatenation
+* Add `array.filter` function
 
 ### Other changes
 

docs/src/builtin_methods.md

@@ -57,6 +57,16 @@ Applies the function `f` to each element of the array and returns a new array wi
 [2, 4, 6]
 ```
 
+### `array.filter(function p) -> array`
+
+Applies the predicate `p` to each element and only includes the elements for which the predicate returns `true`.
+
+```javascript
+>> function isEven(x) { return x % 2 == 0; }
+>> [1, 2, 3, 4, 5].filter(isEven)
+[2, 4]
+```
+
 ### `array.concat(array other) -> array`
 
 Concatenates two arrays.
@@ -66,6 +76,7 @@ Concatenates two arrays.
 [1, 2, 3, 4]
 ```
 
+
 ## `tuple` methods
 
 ### `tuple[uint256 index] -> any`

src/interpreter/builtins/iterable.rs

@@ -33,6 +33,31 @@ fn map<'a>(
     .boxed()
 }
 
+fn filter<'a>(
+    env: &'a mut Env,
+    receiver: &'a Value,
+    args: &'a [Value],
+) -> BoxFuture<'a, Result<Value>> {
+    async move {
+        let mut values = vec![];
+        for v in receiver.get_items()? {
+            match args.first() {
+                Some(Value::Func(func)) => match func.execute(env, &[v.clone()]).await? {
+                    Value::Bool(true) => values.push(v),
+                    Value::Bool(false) => continue,
+                    _ => bail!("filter function must return a boolean"),
+                },
+                _ => bail!("filter function expects a function as an argument"),
+            };
+        }
+        match receiver.get_type() {
+            Type::Array(t) => Ok(Value::Array(values, t.clone())),
+            ty => bail!("cannot map to type {}", ty),
+        }
+    }
+    .boxed()
+}
+
 pub fn iter_len(_env: &Env, arg: &Value) -> Result<Value> {
     arg.len().map(Into::into)
 }
@@ -43,5 +68,10 @@ lazy_static! {
         map,
         vec![vec![FunctionParam::new("f", Type::Function)]]
     );
+    pub static ref ITER_FILTER: Arc<dyn FunctionDef> = AsyncMethod::arc(
+        "filter",
+        filter,
+        vec![vec![FunctionParam::new("p", Type::Function)]]
+    );
     pub static ref ITER_LEN: Arc<dyn FunctionDef> = SyncProperty::arc("length", iter_len);
 }

src/interpreter/builtins/mod.rs

@@ -62,6 +62,7 @@ lazy_static! {
         let mut array_methods = HashMap::new();
         array_methods.insert("length".to_string(), ITER_LEN.clone());
         array_methods.insert("map".to_string(), iterable::ITER_MAP.clone());
+        array_methods.insert("filter".to_string(), iterable::ITER_FILTER.clone());
         array_methods.insert("concat".to_string(), concat::CONCAT.clone());
         array_methods.insert("format".to_string(), format::NON_NUM_FORMAT.clone());
         m.insert(NonParametricType::Array, array_methods);