3 files changed, 11 insertions, 3 deletions
diff --git a/src/evaluator.zig b/src/evaluator.zig
index ec5df8c..2fc5441 100644
--- a/src/evaluator.zig
+++ b/src/evaluator.zig
@@ -136,7 +136,8 @@ pub const Evaluator = struct {
             .ADDITIVE_EXPRESSION => |x| {
                 const lhs = try self.get_expression_value(x.lhs);
                 const rhs = try self.get_expression_value(x.rhs);
-                return lhs + rhs;
+                if (x.addition) return lhs + rhs;
+                return lhs - rhs;
             },
             .PRIMARY_EXPRESSION => |x| {
                 switch (x) {
diff --git a/src/parser.zig b/src/parser.zig
index 81006f8..36f7437 100644
--- a/src/parser.zig
+++ b/src/parser.zig
@@ -48,6 +48,7 @@ pub const Node = union(NodeType) {
         },
     },
     ADDITIVE_EXPRESSION: struct {
+        addition: bool,
         lhs: *Node,
         rhs: *Node,
     },
@@ -216,15 +217,18 @@ pub const Parser = struct {
             return ParserError.ParsingError;
     }
 
-    // AdditiveExpression ::= PrimaryExpression ("+" AdditiveExpression)
+    // AdditiveExpression ::= PrimaryExpression (("+" | "-") AdditiveExpression)
     fn parse_additive_expression(self: *Parser) ParserError!*Node {
         errdefer if (!self.try_context) std.debug.print("Error parsing additive expression\n", .{});
 
         const lhs = try self.parse_primary_expression();
 
-        if (self.accept_token(tokenizer.TokenType.PLUS) != null) {
+        const plus = self.accept_token(tokenizer.TokenType.PLUS);
+        const minus = self.accept_token(tokenizer.TokenType.MINUS);
+        if (plus != null or minus != null) {
             const rhs = try self.parse_additive_expression();
             return self.create_node(.{ .ADDITIVE_EXPRESSION = .{
+                .addition = plus != null,
                 .lhs = lhs,
                 .rhs = rhs,
             } });
diff --git a/src/tokenizer.zig b/src/tokenizer.zig
index f5908b2..e395835 100644
--- a/src/tokenizer.zig
+++ b/src/tokenizer.zig
@@ -20,6 +20,7 @@ pub const TokenType = enum {
     // Operators
     EQUALS,
     PLUS,
+    MINUS,
 
     // Punctuation
     SEMICOLON,
@@ -39,6 +40,7 @@ pub const Token = union(TokenType) {
     NUMBER: i64,
     EQUALS: void,
     PLUS: void,
+    MINUS: void,
     SEMICOLON: void,
     COMMA: void,
     LPAREN: void,
@@ -74,6 +76,7 @@ pub const Tokenizer = struct {
         if (c == '}') return Token{ .RBRACE = void{} };
         if (c == '=') return Token{ .EQUALS = void{} };
         if (c == '+') return Token{ .PLUS = void{} };
+        if (c == '-') return Token{ .MINUS = void{} };
 
         const string = self.consume_string();
         if (string.len == 0) return TokenizerError.TokenizingError;