I found a strange behavior with #'\\Z', I wonder if it is a bug or if it is normal.

((insta/parser
   "Paragraph = NonBlankLine+ BlankLine+
    BlankLine = #'[ \\t]'* EOL
    NonBlankLine = #'\\S'+ EOL
    EOL = (#'\\n' | EOF)
    EOF = #'\\Z'")
 "abc\ndef\n")

=> 
[:Paragraph
 [:NonBlankLine "a" "b" "c" [:EOL "\n"]]
 [:NonBlankLine "d" "e" "f" [:EOL [:EOF ""]]]
 [:BlankLine [:EOL "\n"]]]

EOF appears before "\n" in the parsed result.

This other approach which uses the negative lookahead does put the "\n" in the right place in the result, but there is another problem: The BlankLine is missing in the result. That may be a bug of instaparse. I am using the version 1.4.9.

((insta/parser
   "Paragraph = NonBlankLine+ BlankLine+
    BlankLine = #'[ \\t]'* EOL
    NonBlankLine = #'\\S'+ EOL
    EOL = (#'\\n' | EOF)
    EOF = !#'.'")
 "abc\ndef\n")
=>
[:Paragraph [:NonBlankLine "a" "b" "c" [:EOL "\n"]]
            [:NonBlankLine "d" "e" "f" [:EOL "\n"]]]

I am going to use this workaround for now: append “EOF” at the end of the input and parse it. It works very well 🙂

((insta/parser
   "Paragraph = NonBlankLine+ BlankLine+
    BlankLine = #'[ \\t]'* EOL
    NonBlankLine = #'\\S'+ EOL
    EOL = (#'\\n' | EOF)
    EOF = 'EOF' #'\\Z'") ; works as well with !#'.'
 "abc\ndef\nEOF")
=>
[:Paragraph
 [:NonBlankLine "a" "b" "c" [:EOL "\n"]]
 [:NonBlankLine "d" "e" "f" [:EOL "\n"]]
 [:BlankLine [:EOL [:EOF "EOF" ""]]]]

love instaparse