make `detect-paragraphs` work more intuitively

decode.rkt

@@ -350,10 +350,11 @@
       [(list (? block-txexpr? bxs) ...) bxs] ; leave a series of block xexprs alone
       [else (list (make-txexpr tag empty elems))])) ; otherwise wrap in p tag
   
-  (let ([elements (prep-paragraph-flow elements)]) 
-    (if (ormap my-paragraph-break? elements) ; need this condition to prevent infinite recursion
-        ;; use append-map rather than map to permit return of multiple elements
-        (append-map wrap-paragraph (filter-split elements my-paragraph-break?)) ; split into ¶¶
+  (let ([elements (prep-paragraph-flow elements)])
+    (define explicit-or-implicit-paragraph-break? (λ(x) (or (my-paragraph-break? x) (block-txexpr? x))))
+    (if (ormap explicit-or-implicit-paragraph-break? elements) ; need this condition to prevent infinite recursion
+        ;; use append-map on wrap-paragraph rather than map to permit return of multiple elements
+        (append-map wrap-paragraph (append-map (λ(es) (filter-split es my-paragraph-break?)) (slicef elements block-txexpr?))) ; split into ¶¶, using both implied and explicit paragraph breaks
         (if force-paragraph
             (append-map wrap-paragraph (slicef elements block-txexpr?)) ; upconverts non-block elements to paragraphs
             elements))))                

scribblings/decode.scrbl

@@ -330,26 +330,44 @@ Within @racket[_tagged-xexpr-elements], convert occurrences of @racket[_linebrea
 [#:linebreak-proc linebreak-proc (txexpr-elements? . -> . txexpr-elements?) detect-linebreaks]
 [#:force? force-paragraph? boolean? #f])
 txexpr-elements?]
-Find paragraphs within @racket[_elements] (as denoted by @racket[_paragraph-sep]) and wrap them with @racket[_paragraph-tag]. Also handle linebreaks using @racket[detect-linebreaks].
+Find paragraphs within @racket[_elements] and wrap them with @racket[_paragraph-tag]. Also handle linebreaks using @racket[detect-linebreaks].
 
-If @racket[_element] is already a @racket[block-txexpr?], it will not be wrapped as a paragraph (because in that case, the wrapping would be superfluous). Thus, as a consequence, if @racket[_paragraph-sep] occurs between two blocks, it will be ignored (as in the example below using two sequential @racket['div] blocks.) 
+What counts as a paragraph? Any @racket[_elements] that are either a) explicitly set apart with @racket[_paragraph-sep], or b) adjacent to a @racket[block-txexpr?] (in which case the paragraph-ness is implied).
 
-The @racket[_paragraph-tag] argument sets the tag used to wrap paragraphs. 
-
-The @racket[_linebreak-proc] argument allows you to use a different linebreaking procedure other than the usual @racket[detect-linebreaks].
+@examples[#:eval my-eval
+(detect-paragraphs '("Explicit para" "\n\n" "Explicit para"))
+(detect-paragraphs '("Explicit para" "\n\n" "Explicit para" "\n" "Explicit line"))
+(detect-paragraphs '("Implied para" (div "Block") "Implied para"))
+]
 
-The @racket[#:force?] option will wrap a paragraph tag around @racket[_elements], even if no paragraph break is found. If any @racket[_element] is already a @racket[block-txexpr?], it is skipped, but the remaining sequences of non-block @racket[_elements] are wrapped. The @racket[#:force?] option is useful for when you want to guarantee that you get a list of blocks.
+If @racket[_element] is already a block, it will not be wrapped as a paragraph (because in that case, the wrapping would be superfluous). Thus, as a consequence, if @racket[_paragraph-sep] occurs between two blocks, it will be ignored (as in the example below using two sequential @racket[div] blocks.) Likewise, @racket[_paragraph-sep] will also be ignored if it occurs between a block and a non-block (because a paragraph break is already implied).
 
 @examples[#:eval my-eval
-(detect-paragraphs '("First para" "\n\n" "Second para"))
-(detect-paragraphs '("First para" "\n\n" "Second para" "\n" "Second line"))
-(detect-paragraphs '("First para" "\n\n" (div "Second block")))
+(code:comment @#,t{The explicit "\n\n" makes no difference in these cases})
 (detect-paragraphs '((div "First block") "\n\n" (div "Second block")))
+(detect-paragraphs '((div "First block") (div "Second block")))
+(detect-paragraphs '("Para" "\n\n" (div "Block")))
+(detect-paragraphs '("Para" (div "Block")))
+]
+
+The @racket[_paragraph-tag] argument sets the tag used to wrap paragraphs. 
+
+@examples[#:eval my-eval
 (detect-paragraphs '("First para" "\n\n" "Second para") #:tag 'ns:p)
+]
+
+The @racket[_linebreak-proc] argument allows you to use a different linebreaking procedure other than the usual @racket[detect-linebreaks].
+
+@examples[#:eval my-eval
 (detect-paragraphs '("First para" "\n\n" "Second para" "\n" "Second line")
 #:linebreak-proc (λ(x) (detect-linebreaks x #:insert '(newline))))
-(detect-paragraphs '("First" (span "para") (div "Block") "Second para") 
-#:force? #t)
+]
+
+The @racket[#:force?] option will wrap a paragraph tag around @racket[_elements], even if no explicit or implicit paragraph breaks are found. The @racket[#:force?] option is useful for when you want to guarantee that you always get a list of blocks.
+
+@examples[#:eval my-eval
+(detect-paragraphs '("This" (span "will not be") "a paragraph"))
+(detect-paragraphs '("But this" (span "will be") "a paragraph") #:force? #t)
 ]
 
 @defproc[

tests/tests-decode.rkt

@@ -58,14 +58,13 @@
 (check-equal? (detect-paragraphs '("foo") #:force? #t) '((p "foo")))
 (check-equal? (detect-paragraphs '((div "foo"))) '((div "foo")))
 (check-equal? (detect-paragraphs '((div "foo")) #:force? #t) '((div "foo")))
-(check-equal? (detect-paragraphs '("foo" (div "bar"))) '("foo" (div "bar")))
+(check-equal? (detect-paragraphs '("foo" "\n\n" (div "bar"))) '((p "foo") (div "bar")))
+(check-equal? (detect-paragraphs '("foo" (div "bar"))) '((p "foo") (div "bar")))
 (check-equal? (detect-paragraphs '("foo" (div "bar")) #:force? #t) '((p "foo") (div "bar")))
-(check-equal? (detect-paragraphs '("foo" (div "bar") "zam")) '("foo" (div "bar") "zam"))
-(check-equal? (detect-paragraphs '("foo" (span "zing") (div "bar") "zam")) '("foo" (span "zing") (div "bar") "zam"))
+(check-equal? (detect-paragraphs '("foo" (div "bar") "zam")) '((p "foo") (div "bar") (p "zam")))
+(check-equal? (detect-paragraphs '("foo" (span "zing") (div "bar") "zam")) '((p "foo" (span "zing")) (div "bar") (p "zam")))
 (check-equal? (detect-paragraphs '("foo" (span "zing") (div "bar") "zam") #:force? #t) '((p "foo" (span "zing")) (div "bar") (p "zam")))
 
-
-
 (check-equal? (merge-newlines '(p "\n" "foo" "\n" "\n" "bar" (em "\n" "\n" "\n"))) 
               '(p "\n" "foo" "\n\n" "bar" (em "\n\n\n")))