ast: allow definitions in loop head

This is a rather bad hack, but it makes parsing a
lot easier, so i'll allow it for now.

src/ast/mod.rs

@@ -17,6 +17,7 @@ enum Scope {
     SourceList,
     Function,
     Loop,
+    ForLoopHead,
 }
 
 struct Parser {
@@ -243,6 +244,7 @@ impl Parser {
         self.lexer.expect_kind(token::Kind::OParen)?;
         let terminators = [token::Kind::Semi, token::Kind::Semi, token::Kind::CParen];
         let mut exprs = Vec::new();
+        self.scope.push(Scope::ForLoopHead);
         for i in 0..3 {
             exprs.push(if self.lexer.next_if(terminators[i]).is_some() {
                 None
@@ -250,6 +252,7 @@ impl Parser {
                 Some(self.parse_expr(&terminators[i..=i])?)
             });
         }
+        self.scope.pop();
         let body = self.parse_block_stmt()?;
         self.scope.pop();
         let exec = exprs.pop().unwrap();
@@ -330,10 +333,15 @@ impl Parser {
         self.assert_scope(Scope::File)?;
         let expr = if let Some(result) = self.lexer.peek() {
             let token = result?;
-            if !token.kind.is_start_of_expr() {
+            match token.kind {
-                self.syntax_error(String::from("Expected an expression"), &token)
+                k if k.is_start_of_expr() => self.parse_assignment_expr_or_higher(terminators),
-            } else {
+                // special case: when we are in a for loop header, we allow
-                self.parse_assignment_expr_or_higher(terminators)
+                // declaration statements (this is technically a bug and we're
+                // only doing it because it makes parsing everything easier)
+                token::Kind::VarKeyword if self.is_scope(Scope::ForLoopHead) => {
+                    self.parse_decl_stmt()
+                }
+                _ => self.syntax_error(String::from("Expected an expression"), &token),
             }
         } else {
             self.syntax_error(
@@ -707,6 +715,10 @@ impl Parser {
         }
     }
 
+    fn is_scope(&self, scope: Scope) -> bool {
+        self.assert_scope(scope).is_ok()
+    }
+
     /// Ensure that the `scope` stack does not contain a certain scope.
     fn assert_scope_not(&self, scope: Scope) -> Result<(), Error> {
         if self.scope.contains(&scope) {

src/main.rs

@@ -3,20 +3,29 @@ mod error;
 mod lex;
 mod rt;
 
+use std::time::Instant;
+
 use ast::parse;
 use rt::exec;
 
 fn main() {
+    let start_time = Instant::now();
     let result = parse(String::from("test.gaybuild")).unwrap();
+    let duration = start_time.elapsed();
     match result {
         Ok(tree) => {
             println!("=== begin tree ===");
             tree.walk(|n, d| println!("{}{}", "    ".repeat(d as usize), n));
-            println!("=== end tree ===\n");
+            println!("=== end tree ===");
+            println!("parsing took {:?}\n", duration);
             println!("=== begin eval ===");
-            match exec(&tree) {
+            let start_time = Instant::now();
+            let result = exec(&tree);
+            let duration = start_time.elapsed();
+            match result {
                 Ok(val) => {
                     println!("=== end eval ===");
+                    println!("evaluation took {:?}", duration);
                     println!("evaluation returned {}", val)
                 }
                 Err(e) => println!("{:?}", e),

test.gaybuild

@@ -31,7 +31,7 @@ target kern {
         print("2 <= 3");
     }
     # ... so do while loops ...
-    y = 0;
+    var y = 0;
     while (true) {
         print(y);
         y += 1;
@@ -40,19 +40,24 @@ target kern {
         }
     }
     # ... and even for loops
-    for (x = 0; x < 10; x += 1) {
+    for (var x = 0; x < 10; x += 1) {
         print(x);
     }
 
     # functions are first-class citizens; they can be defined as inline
     # anonymous functions that you can treat like any other value
-    fn_with_callback(fn(a, b) { return a + b; });
+    var captured_val = "-.-";
+    fn_with_callback(fn(a, b) {
+        captured_val = "OwO";
+        return a + b;
+    });
+    print(captured_val);
     (fn(a, b) { return a + b; })(1, 2);
 
     # math works exactly as you would expect it to
-    owo = 1 + 2 * 3 * 4 - 5;
+    var owo = 1 + 2 * 3 * 4 - 5;
     # and, naturally, there are also all the bitwise goodies
-    bitmask = 1 << 2 | 1 << 8 ^ get_bit() & 1;
+    var bitmask = 1 << 2 | 1 << 8 ^ get_bit() & 1;
     # this is exactly equal to the above, but with added
     # parentheses to make the operator precedences clear
     bitmask = (1 << 2) | ((1 << 8) ^ (get_bit() & 1));