Implement quote, quasiquote, unquote and unquote-splice special forms (wip)

Author: winpat

src/parser.zig

@@ -51,6 +51,10 @@ pub const Parser = struct {
             .rparen => return ParseError.UnexpectedRightParen,
             .lbracket => self.parseVector(allocator, tk.line),
             .rbracket => return ParseError.UnexpectedRightBracket,
+            .quote => try self.wrapExpr(allocator, tk.line, "quote"),
+            .quasiquote => try self.wrapExpr(allocator, tk.line, "quasiquote"),
+            .unquote => try self.wrapExpr(allocator, tk.line, "unquote"),
+            .unquote_splice => try self.wrapExpr(allocator, tk.line, "unquote_splice"),
         };
     }
 
@@ -85,13 +89,27 @@ pub const Parser = struct {
             },
         };
     }
+
+    fn wrapExpr(self: *Parser, allocator: Allocator, line: u32, sym: []const u8) ParseError!Node {
+        const tk = try self.scanner.scanToken() orelse return ParseError.MissingExpr;
+        const expr = try self.parseExpr(allocator, tk);
+        const items = &[_]Node{ .{ .symbol = .{ .name = sym, .line = line } }, expr };
+
+        return Node{
+            .list = Node.List{
+                .items = try allocator.dupe(Node, items),
+                .line = line,
+            },
+        };
+    }
 };
 
 pub const ParseError = error{
     UnexpectedRightParen,
     UnexpectedRightBracket,
     MissingRightParen,
     MissingRightBracket,
+    MissingExpr,
 } || scanner.ScanError || fmt.ParseFloatError || Allocator.Error;
 
 pub const AbstractSyntaxTree = struct { nodes: []const Node };
@@ -198,6 +216,13 @@ test "Parse keyword" {
     );
 }
 
+// test "Parse quote" {
+//     try expectAstWithOneNode(
+//         "'",
+//         .{ .quote = .{ .name = "'", .line = 1 } },
+//     );
+// }
+
 test "Parse string" {
     try expectAstWithOneNode(
         "\"Hello World!\"",

src/scanner.zig

@@ -21,6 +21,12 @@ pub const Scanner = struct {
                 ')' => break self.createToken(.rparen),
                 '[' => break self.createToken(.lbracket),
                 ']' => break self.createToken(.rbracket),
+                '\'' => break self.createToken(.quote),
+                '`' => break self.createToken(.quasiquote),
+                '~' => if (self.peek() == '@') {
+                    self.pos += 1;
+                    break self.createToken(.unquote_splice);
+                } else break self.createToken(.unquote),
                 '"' => break try self.scanString(),
                 ':' => break try self.scanKeyword(),
                 '0'...'9' => break self.scanNumber(),
@@ -151,6 +157,10 @@ pub const Token = struct {
         nil,
         boolean_true,
         boolean_false,
+        quote,
+        quasiquote,
+        unquote,
+        unquote_splice,
     };
     tag: Tag,
     lexeme: []const u8,
@@ -247,6 +257,34 @@ test "Scan right bracket" {
     );
 }
 
+test "Scan quote" {
+    try expectToken(
+        "'",
+        Token{ .tag = .quote, .lexeme = "'", .line = 1 },
+    );
+}
+
+test "Scan quasiquote" {
+    try expectToken(
+        "`",
+        Token{ .tag = .quasiquote, .lexeme = "`", .line = 1 },
+    );
+}
+
+test "Scan unquote" {
+    try expectToken(
+        "~",
+        Token{ .tag = .unquote, .lexeme = "~", .line = 1 },
+    );
+}
+
+test "Scan unquote splice" {
+    try expectToken(
+        "~@",
+        Token{ .tag = .unquote_splice, .lexeme = "~@", .line = 1 },
+    );
+}
+
 test "Scan string" {
     try expectToken(
         "\"hello\"",