Improve parser error handling

src/error.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const token = @import("token.zig");
 
 pub var hasError: bool = false;
 
@@ -6,7 +7,20 @@ pub fn err(line: u64, message: []const u8) void {
     report(line, "", message);
 }
 
-pub fn report(line: u64, where: []u8, message: []const u8) void {
+pub fn errToken(tok: token.Token, message: []const u8) void {
+    if (tok.token_type == token.TokenType.EOF) {
+        report(tok.line, " at end", message);
+    } else {
+        var buffer = [_]u8{0} ** 100;
+        const where = std.fmt.bufPrint(&buffer, " at '{s}'", .{tok.lexeme}) catch {
+            std.debug.print("Format error: buffer empty", .{});
+            std.process.exit(1);
+        };
+        report(tok.line, where, message);
+    }
+}
+
+pub fn report(line: u64, where: []const u8, message: []const u8) void {
     std.debug.print("[line {}] Error{s}: {s}\n", .{ line, where, message });
     hasError = true;
 }

src/main.zig

@@ -67,8 +67,10 @@ fn run(allocator: std.mem.Allocator, bytes: []u8) !void {
         .allocator = alloc,
     };
 
-    const expression = try parse.expression();
-    // std.debug.print("AST: {}", .{expression.*});
-    expr.AstPrint(expression.*);
+    const expression = parse.parse();
+    if (err.hasError) {
+        return;
+    }
+    expr.AstPrint(expression);
     std.debug.print("\n", .{});
 }

src/parser.zig

@@ -13,6 +13,12 @@ const Token = token_zig.Token;
 
 const errors_zig = @import("error.zig");
 const err = errors_zig.err;
+const errToken = errors_zig.errToken;
+
+const ParseError = error{
+    UnmatchedParen,
+    UnexpectedToken,
+};
 
 pub const Parser = struct {
     const Self = @This();
@@ -20,11 +26,20 @@ pub const Parser = struct {
     allocator: std.mem.Allocator,
     current: u64 = 0,
 
-    pub fn expression(self: *Self) !*Expr {
+    pub fn parse(self: *Self) Expr {
+        var expr = self.expression() catch blk: {
+            break :blk &Expr{ .literal = LiteralExpr{
+                .nil = false,
+            } };
+        };
+        return expr.*;
+    }
+
+    fn expression(self: *Self) !*Expr {
         return self.equality();
     }
 
-    pub fn equality(self: *Self) !*Expr {
+    fn equality(self: *Self) !*Expr {
         var expr = try self.comparison();
 
         while (true) {
@@ -128,7 +143,7 @@ pub const Parser = struct {
         }
     }
 
-    fn primary(self: *Self) error{OutOfMemory}!*Expr {
+    fn primary(self: *Self) error{ OutOfMemory, UnmatchedParen, UnexpectedToken }!*Expr {
         var expr = try self.allocator.create(Expr);
         const token = self.advance();
         switch (token.token_type) {
@@ -143,12 +158,13 @@ pub const Parser = struct {
                 };
                 var next_token = self.advance();
                 if (next_token.token_type != TokenType.RIGHT_PAREN) {
-                    err(next_token.line, "Unclosed left paren.");
+                    errToken(next_token, "Unclosed left paren.");
+                    return ParseError.UnmatchedParen;
                 }
             },
             else => {
-                err(token.line, "Unexpected primary token type.");
-                expr.* = Expr{ .literal = LiteralExpr{ .nil = false } };
+                errToken(token, "Unexpected token.");
+                return ParseError.UnexpectedToken;
             },
         }
         return expr;