Refactor map and record representation

Replaces the use of `BTreeMap` and `HashMap` for maps and records with
`Vec<(Keyword, Value)>` and `Vec<(Keyword, StaticType)>`. This
simplifies the data structure and allows for ordered iteration, which is
important for serialization and comparison.

Also updates the `unpack` function in `vm.rs` to handle records as well
as lists when destructuring.

src/ast/types.rs

@@ -1,4 +1,4 @@
-use std::collections::{HashMap, BTreeMap};
+use std::collections::HashMap;
 use std::rc::Rc;
 use std::cell::RefCell;
 use std::fmt;
@@ -66,7 +66,7 @@ pub enum Value {
     Text(Rc<str>),
     Keyword(Keyword),
     List(Rc<Vec<Value>>),
-    Record(Rc<HashMap<Keyword, Value>>),
+    Record(Rc<Vec<(Keyword, Value)>>),
     Function(Rc<dyn Fn(Vec<Value>) -> Value>),
     Object(Rc<dyn Object>), // For compiled Closures and other opaque types
     Cell(Rc<RefCell<Value>>), // Boxed value for captures
@@ -93,7 +93,7 @@ pub enum StaticType {
     Tuple(Vec<StaticType>), // Heterogeneous fixed-size
     Vector(Box<StaticType>, usize), // Homogeneous fixed-size
     Matrix(Box<StaticType>, Vec<usize>), // Multi-dimensional homogeneous
-    Record(Rc<BTreeMap<Keyword, StaticType>>),
+    Record(Rc<Vec<(Keyword, StaticType)>>),
     Function(Box<Signature>),
     FunctionOverloads(Vec<Signature>),
     Object(&'static str),
@@ -255,9 +255,9 @@ impl Value {
                 }
             },
             Value::Record(r) => {
-                let mut fields = BTreeMap::new();
+                let mut fields = Vec::with_capacity(r.len());
                 for (k, v) in r.iter() {
-                    fields.insert(*k, v.static_type());
+                    fields.push((*k, v.static_type()));
                 }
                 StaticType::Record(Rc::new(fields))
             },
@@ -293,10 +293,8 @@ impl fmt::Display for Value {
                 write!(f, "]")
             },
             Value::Record(r) => {
-                let mut entries: Vec<_> = r.iter().collect();
-                entries.sort_by_key(|(k, _)| k.name());
                 write!(f, "{{")?;
-                for (i, (k, v)) in entries.iter().enumerate() {
+                for (i, (k, v)) in r.iter().enumerate() {
                     if i > 0 { write!(f, ", ")?; }
                     write!(f, ":{} {}", k.name(), v)?;
                 }