From d2fe2073f00c98771fc895405dd4d094a34ba7b7 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Mon, 29 Oct 2018 17:13:01 -0700
Subject: [PATCH] splice

---
 pollen/private/splice.rkt | 46 +++++++++++++++++++--------------------
 pollen/private/ts.rktd    |  2 +-
 2 files changed, 23 insertions(+), 25 deletions(-)

diff --git a/pollen/private/splice.rkt b/pollen/private/splice.rkt
index a3ab1d5..556b088 100644
--- a/pollen/private/splice.rkt
+++ b/pollen/private/splice.rkt
@@ -1,31 +1,33 @@
 #lang racket/base
+(require racket/match
+         racket/list)
 (provide (all-defined-out))
 
 ;; (string->symbol (format "~a" #\u200B))
 (define splice-signal-tag '@)
 
 (define (attrs? x)
-  (and (list? x)
-       (andmap (λ (xi)
-                 (and (list? xi)
-                      (= (length xi) 2)
-                      (symbol? (car xi))
-                      (string? (cadr xi)))) x)))
+  (match x
+    [(list (list (? symbol?) (? string?)) ...) #true]
+    [_ #false]))
 
+(define (null-string? x) (equal? x ""))
+
+(define ((spliceable? splicing-tag) x)
+  (match x
+    [(cons (== splicing-tag eq?) _) #true]
+    [_ #false]))
 
 (define (splice x [splicing-tag splice-signal-tag])
   ;  (listof txexpr-elements?) . -> . (listof txexpr-elements?))
-  (define spliceable? (λ (x) (and (pair? x) (eq? (car x) splicing-tag))))
-  (define not-null-string? (λ (x) (not (and (string? x) (zero? (string-length x))))))
   (let loop ([x x])
     (if (list? x) ; don't exclude `attrs?` here, because it will exclude valid splice input like '((@ "foo"))
-        (apply append (map (λ (x) (let ([proc (if (spliceable? x) ; drop the splice-signal from front with `cdr`
-                                                  cdr
-                                                  list)]
-                                        [x (if (not (attrs? x)) ; don't recur on attributes, so null strings are not spliced within
-                                               (loop x)
-                                               x)])
-                                    (proc x))) (filter not-null-string? x)))
+        (append-map (λ (x)
+                      ; drop the splice-signal from front with `rest`
+                      ; don't recur on attributes, so null strings are not spliced within
+                      (define proc (if ((spliceable? splicing-tag) x) rest list))
+                      (proc (if (attrs? x) x (loop x))))
+                    (filter-not null-string? x))
         x)))
 
 (module+ test
@@ -40,29 +42,25 @@
   (check-equal? (splice `((,splice-signal-tag "str"))) '("str")))
 
 
+;; this will strip all empty lists.
+;; in practice, they would only appear in attrs position 
 (define (strip-empty-attrs x)
   (let loop ([x x])
-    (if (list? x)
-        ;; this will strip all empty lists.
-        ;; in practice, they would only appear in attrs position 
-        (map loop (filter (λ (x) (not (null? x))) x))
+    (if (pair? x)
+        (map loop (filter-not null? x))
         x)))
 
-
 (module+ test
   (check-equal? (strip-empty-attrs '(p ())) '(p))
   (check-equal? (strip-empty-attrs '(p () "foo")) '(p "foo"))
   (check-equal? (strip-empty-attrs '(p () (em () "foo") "bar")) '(p (em "foo") "bar")))
 
-
 ;; used with pollen/markup to suppress void arguments,
 ;; consistent with how pollen/pre and pollen/markdown handle them
 (define (remove-voids x)
   (let loop ([x x])
     (if (pair? x)
-        (for/list ([xi (in-list x)]
-                   #:unless (void? xi))
-                  (loop xi))
+        (map loop (filter-not void? x))
         x)))
 
 (module+ test
diff --git a/pollen/private/ts.rktd b/pollen/private/ts.rktd
index 2755309..6e391b1 100644
--- a/pollen/private/ts.rktd
+++ b/pollen/private/ts.rktd
@@ -1 +1 @@
-1540858378
+1540858381