Add async statements

README.md

@@ -11,8 +11,10 @@ A basic dust program:
 Dust can do two (or more) things at the same time with effortless concurrency:
 
 ```dust
-async (output 'will this one finish first?')
-async (output 'or will this one?')
+async {
+    (output 'will this one finish first?')
+    (output 'or will this one?')
+}
 ```
 
 Dust is an interpreted, general purpose language with first class functions. It is *data-oriented*, with extensive tools to manage structured and relational data. Dust also includes built-in tooling to import and export data in a variety of formats, including JSON, TOML, YAML and CSV.
@@ -28,6 +30,7 @@ Dust is an interpreted, general purpose language with first class functions. It
     - [Maps](#maps)
     - [Tables](#tables)
     - [Functions](#functions)
+    - [Concurrency](#concurrency)
   - [Implementation](#implementation)
 <!--toc:end-->
 
@@ -176,14 +179,22 @@ print = function <input> {
 As a language written in Rust, Dust features effortless concurrency anywhere in your code.
 
 ```dust
-if (random_integer) % 2 == 0 {
-    run {
-        (output 1 + 1)
-        (output 1 + 1 == 2)
-    }
+async {
+    await 1 + 1
 }
 ```
 
+The **await** keyword can be used in an asnyc block to indicate what value the async block should evaluate to. In this case, we want "data" to be read from a file.
+
+```dust
+data = async {
+    (output "Reading a file...")
+    (read "examples/assets/faithful.csv")
+}
+
+(output data)
+```
+
 ## Implementation
 
 Dust is formally defined as a Tree Sitter grammar in the tree-sitter-dust module. Tree sitter generates a parser, written in C, from a set of rules defined in Javascript. Dust itself is a rust binary that calls the C parser using FFI.

src/abstract_tree/async.rs

@@ -1,23 +1,60 @@
+use rayon::prelude::*;
 use serde::{Deserialize, Serialize};
+use tree_sitter::Node;
 
-use crate::{AbstractTree, Item};
+use crate::{AbstractTree, Error, Result, Statement, Value, VariableMap};
 
 #[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord)]
 pub struct Async {
-    item: Item,
+    statements: Vec<Statement>,
 }
 
 impl AbstractTree for Async {
-    fn from_syntax_node(source: &str, node: tree_sitter::Node) -> crate::Result<Self> {
+    fn from_syntax_node(source: &str, node: Node) -> Result<Self> {
         debug_assert_eq!("async", node.kind());
 
-        let item_node = node.child(2).unwrap();
-        let item = Item::from_syntax_node(source, item_node)?;
+        let child_count = node.child_count();
+        let mut statements = Vec::with_capacity(child_count);
 
-        Ok(Async { item })
+        for index in 2..child_count - 1 {
+            let child = node.child(index).unwrap();
+
+            let statement = match child.kind() {
+                "statement" => Statement::from_syntax_node(source, child)?,
+                _ => {
+                    return Err(Error::UnexpectedSyntaxNode {
+                        expected: "comment or statement",
+                        actual: child.kind(),
+                        location: child.start_position(),
+                        relevant_source: source[child.byte_range()].to_string(),
+                    })
+                }
+            };
+
+            statements.push(statement);
+        }
+
+        Ok(Async { statements })
     }
 
-    fn run(&self, source: &str, context: &mut crate::VariableMap) -> crate::Result<crate::Value> {
-        self.item.run_parallel(source, context)
+    fn run(&self, source: &str, context: &mut VariableMap) -> Result<Value> {
+        let statements = &self.statements;
+
+        statements
+            .into_par_iter()
+            .enumerate()
+            .find_map_last(|(index, statement)| {
+                let mut context = context.clone();
+                let result = statement.run(source, &mut context).unwrap_or_default();
+
+                if index == statements.len() - 1 {
+                    Some(result)
+                } else {
+                    None
+                }
+            })
+            .ok_or(Error::CustomMessage(
+                "Async block has nothing to run.".to_string(),
+            ))
     }
 }

src/abstract_tree/item.rs

@@ -22,13 +22,16 @@ impl Item {
     }
 
     pub fn run_parallel(&self, source: &str, context: &mut VariableMap) -> Result<Value> {
-        self.statements.par_iter().for_each(|statement| {
+        let statements = &self.statements;
+        let run_result = statements.into_par_iter().try_for_each(|statement| {
             let mut context = context.clone();
-
-            statement.run(source, &mut context);
+            statement.run(source, &mut context).map(|_| ())
         });
 
-        Ok(Value::Empty)
+        match run_result {
+            Ok(()) => Ok(Value::Empty),
+            Err(error) => Err(error),
+        }
     }
 }
 

tree-sitter-dust

@@ -1 +1 @@
-Subproject commit 0f58ea5a7a05d49d99bbe24b9da03eea5249cbd7
+Subproject commit cf22950b7ee6f40c7840b6af4d7b2dda69f4965b