1 files changed, 50 insertions, 0 deletions
diff --git a/src/parse.zig b/src/parse.zig
new file mode 100644
index 0000000..8ceabeb
--- /dev/null
+++ b/src/parse.zig
@@ -0,0 +1,50 @@
+pub const Expr = union(enum) {
+    IntegerLiteral: Token,
+    BinOp: struct { lhs: *const Expr, op: Token, rhs: *const Expr },
+    Invalid: Token,
+};
+
+pub fn expression(allocator: Allocator, lexer: *Peekable(Lexer)) error{OutOfMemory}!*Expr {
+    return addExpr(allocator, lexer);
+}
+
+pub fn addExpr(allocator: Allocator, lexer: *Peekable(Lexer)) !*Expr {
+    const lhs = try primaryExpr(allocator, lexer);
+    const token: ?Lexer.Token = lexer.peek();
+    const op = (if (token) |t| if (t.type == .Plus) t else null else null) orelse return lhs;
+    _ = lexer.next();
+
+    const rhs = try primaryExpr(allocator, lexer);
+    return allocate(allocator, .{ .BinOp = .{ .lhs = lhs, .op = op, .rhs = rhs } });
+}
+
+pub fn primaryExpr(allocator: Allocator, lexer: *Peekable(Lexer)) !*Expr {
+    const token = lexer.next().?;
+    // std.debug.print("term {}\n", .{token});
+    return allocate(allocator, switch (token.type) {
+        .LeftParen => {
+            const res = expression(allocator, lexer);
+            const right_paren = lexer.next().?;
+            if (right_paren.type != .RightParen)
+                return allocate(allocator, .{ .Invalid = right_paren });
+            return res;
+        },
+        .IntegerLiteral => .{ .IntegerLiteral = token },
+        else => .{ .Invalid = token },
+    });
+}
+
+fn allocate(allocator: Allocator, expr: Expr) !*Expr {
+    const res = try allocator.create(Expr);
+    res.* = expr;
+    return res;
+}
+
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+
+const Lexer = @import("./lexer.zig");
+const Token = Lexer.Token;
+const root = @import("root");
+const Peekable = root.Peekable;
+const peekable = root.peekable;