diff --git a/18.rkt b/18.rkt
index a5357df..fb5c433 100644
--- a/18.rkt
+++ b/18.rkt
@@ -7,9 +7,9 @@
 (define-tokens nums [number])
 (define-empty-tokens syms [+ * lp rp eof])
 
-(define the-lexer
+(define oo-lexer
   (lexer
-    [whitespace (the-lexer input-port)]
+    [whitespace (oo-lexer input-port)]
     ["+" (token-+)]
     ["*" (token-*)]
     ["(" (token-lp)]
@@ -17,13 +17,13 @@
     [(:+ (char-set "0123456789")) (token-number (string->number lexeme))]
     [(eof) (token-eof)]))
 
-(define the-parser
+(define-simple-macro (make-oo-parser/precs needed-precs ...)
   (parser
     [start exp]
     [end eof]
-    [error (lambda args (error "meow" args))]
+    [error (lambda args (error "not shonks:" args))]
     [tokens nums syms]
-    [precs (left *)(left +)
+    [precs needed-precs ...
            (left lp rp)]
     [grammar
       (exp [(lp exp rp) $2]
@@ -31,28 +31,19 @@
            [(exp * exp) (* $1 $3)]
            [(number) $1])]))
 
-(define (parse/string str)
+(define (parse/string oo-parser str)
   (let ([input (open-input-string str)])
-    (the-parser (lambda () (the-lexer input)))))
+    (oo-parser (thunk (oo-lexer input)))))
 
-;; broken!
-(define (part1 input)
-  (for/sum ([line (in-list input)])
-    (parse/string line)))
+(define-simple-macro (define-part name:id needed-precs ...)
+  (define (name input)
+    (for/sum ([line (in-list input)])
+      (parse/string (make-oo-parser/precs needed-precs ...) line))))
 
-(define (part2 input)
-  (for/sum ([line (in-list input)])
-    (parse/string line)))
+(define-part part1 (left + *))
+(define-part part2 (left *) (left +))
 
-;; parse input file
-(define (parse fname)
-  (define input (file->lines fname))
-  input)
-
-(module+ test
-  (require rackunit)
-  ;; tests here
-  (displayln "no tests :("))
+(define parse file->lines)
 
 (module+ main
   (define input (parse "inputs/18"))