improve `split-metas`

pollen/private/split-metas.rkt

@@ -1,20 +1,25 @@
 #lang racket/base
-(require racket/list)
 (provide (all-defined-out))
 
-(define (split-metas tree meta-key)
-  (define datums (flatten (if (syntax? tree) (syntax->datum tree) tree)))
-  (if (>= (length datums) 3)
-      (for/hasheq ([name (in-list datums)]
-                   [k (in-list (cdr datums))]
-                   [v (in-list (cddr datums))]
-                   #:when (eq? name meta-key))
-                  (values k v))
-      (hasheq)))
+(define (split-metas x meta-key)
+  (apply hasheq
+         (let loop ([x (if (syntax? x) (syntax->datum x) x)])
+           (cond
+             [(list? x) (cond
+                          [(and (= (length x) 3) (eq? (car x) meta-key))
+                           (unless (symbol? (cadr x))
+                             (raise-argument-error 'define-meta "valid meta key" (cadr x)))
+                           (cdr x)] ; list with meta key and meta value
+                          [else (apply append (map loop x))])]
+             [else null]))))
+
 
 (module+ test
   (require rackunit)
+  (check-equal? (split-metas 'root 'define-meta) (hasheq))
   (check-equal? (split-metas '(root) 'define-meta) (hasheq))
+  (check-exn exn:fail:contract? (λ () (split-metas '(root (define-meta 42 "bar")) 'define-meta)))
   (check-equal? (split-metas '(root (div #:kw #f (define-meta foo "bar") "hi") "zim" (define-meta foo "boing") "zam") 'define-meta) '#hasheq((foo . "boing")))
+  (check-equal? (split-metas '(root (div #:kw #f (define-meta foo 'bar) "hi") "zim" (define-meta foo 'boing) "zam") 'define-meta) '#hasheq((foo . 'boing)))
   (check-equal? (split-metas #'(root (define-meta dog "Roxy") (define-meta dog "Lex")) 'define-meta) '#hasheq((dog . "Lex")))
   (check-equal? (split-metas #'(root (define-meta dog "Roxy") (div (define-meta dog "Lex"))) 'define-meta) '#hasheq((dog . "Lex"))))

pollen/private/ts.rktd

@@ -1 +1 @@
-1519530928
+1519582841