Fix the parser, make the function name optional.

src/syntax/ast.rs

@@ -27,7 +27,7 @@ pub struct Program {
 #[derive(Clone, Debug, PartialEq)]
 pub enum TopLevel {
     Statement(Statement),
-    Function(Name, Vec<Name>, Expression),
+    Function(Option<Name>, Vec<Name>, Expression),
 }
 
 /// A Name.

src/syntax/parser.lalrpop

@@ -76,7 +76,14 @@ pub TopLevel: TopLevel = {
 }
 
 Function: TopLevel = {
-    "function" "(" Arguments OptionalComma ")" Expression => unimplemented!(),
+    "function" <opt_name:OptionalName> "(" <args:Arguments> OptionalComma ")" <exp:Expression> =>
+        TopLevel::Function(opt_name, args, exp),
+}
+
+OptionalName: Option<Name> = {
+    <name_start: @L> <v:"<var>"> <name_end: @L> =>
+        Some(Name::new(v, Location::new(file_idx, name_start..name_end))),
+    => None,
 }
 
 Arguments: Vec<Name> = {

src/syntax/pretty.rs

@@ -33,7 +33,11 @@ where
             TopLevel::Function(name, arg_names, body) => allocator
                 .text("function")
                 .append(allocator.space())
-                .append(allocator.text(name.to_string()))
+                .append(
+                    name.as_ref()
+                        .map(|x| allocator.text(x.to_string()))
+                        .unwrap_or_else(|| allocator.nil()),
+                )
                 .append(
                     allocator
                         .intersperse(

src/syntax/validate.rs

@@ -117,7 +117,9 @@ impl TopLevel {
         match self {
             TopLevel::Function(name, arguments, body) => {
                 bound_variables.new_scope();
+                if let Some(name) = name {
                     bound_variables.insert(name.name.clone(), name.location.clone());
+                }
                 for arg in arguments.iter() {
                     bound_variables.insert(arg.name.clone(), arg.location.clone());
                 }