Implement match logic and syntax

examples/match.ds

@@ -0,0 +1,12 @@
+foo_or_bar = match (random_boolean) {
+	true => "foo"
+	false => "bar"
+}
+
+num = match (random_integer) {
+	1 => "one",
+	2 => { "two" },
+	* => "neither",
+}
+
+[foo_or_bar, num]

src/abstract_tree/match.rs

@@ -13,6 +13,7 @@ use crate::{AbstractTree, Error, Expression, Map, Result, Statement, Type, Value
 pub struct Match {
     matcher: Expression,
     options: Vec<(Expression, Statement)>,
+    fallback: Option<Box<Statement>>,
 }
 
 impl AbstractTree for Match {
@@ -24,24 +25,37 @@ impl AbstractTree for Match {
 
         let mut options = Vec::new();
         let mut previous_expression = None;
+        let mut next_statement_is_fallback = false;
+        let mut fallback = None;
 
         for index in 2..node.child_count() {
             let child = node.child(index).unwrap();
 
+            if child.kind() == "*" {
+                next_statement_is_fallback = true;
+            }
+
             if child.kind() == "expression" {
                 previous_expression = Some(Expression::from_syntax_node(source, child, context)?);
             }
 
             if child.kind() == "statement" {
-                if let Some(expression) = &previous_expression {
-                    let statement = Statement::from_syntax_node(source, child, context)?;
+                let statement = Statement::from_syntax_node(source, child, context)?;
 
+                if next_statement_is_fallback {
+                    fallback = Some(Box::new(statement));
+                    next_statement_is_fallback = false;
+                } else if let Some(expression) = &previous_expression {
                     options.push((expression.clone(), statement));
                 }
             }
         }
 
-        Ok(Match { matcher, options })
+        Ok(Match {
+            matcher,
+            options,
+            fallback,
+        })
     }
 
     fn run(&self, source: &str, context: &Map) -> Result<Value> {
@@ -55,7 +69,11 @@ impl AbstractTree for Match {
             }
         }
 
-        Ok(Value::Empty)
+        if let Some(fallback) = &self.fallback {
+            fallback.run(source, context)
+        } else {
+            Ok(Value::Empty)
+        }
     }
 
     fn expected_type(&self, _context: &Map) -> Result<Type> {

src/value/map.rs

@@ -1,4 +1,4 @@
-use serde::{ser::SerializeMap, Deserialize, Serialize};
+use serde::{ser::SerializeMap, Serialize};
 use std::{
     cmp::Ordering,
     collections::BTreeMap,

tree-sitter-dust/grammar.js

@@ -285,9 +285,13 @@ module.exports = grammar({
           '{',
           repeat1(
             seq(
-              $.expression,
+              choice(
+                $.expression,
+                '*',
+              ),
               '=>',
               $.statement,
+              optional(','),
             ),
           ),
           '}',

tree-sitter-dust/src/grammar.json

@@ -896,8 +896,17 @@
               "type": "SEQ",
               "members": [
                 {
-                  "type": "SYMBOL",
-                  "name": "expression"
+                  "type": "CHOICE",
+                  "members": [
+                    {
+                      "type": "SYMBOL",
+                      "name": "expression"
+                    },
+                    {
+                      "type": "STRING",
+                      "value": "*"
+                    }
+                  ]
                 },
                 {
                   "type": "STRING",
@@ -906,6 +915,18 @@
                 {
                   "type": "SYMBOL",
                   "name": "statement"
+                },
+                {
+                  "type": "CHOICE",
+                  "members": [
+                    {
+                      "type": "STRING",
+                      "value": ","
+                    },
+                    {
+                      "type": "BLANK"
+                    }
+                  ]
                 }
               ]
             }