Practical example of Lisp's flexibility? [closed]

Answer 1

See how you can extend Common Lisp with XML templating: cl-quasi-quote XML example, project page,

(babel:octets-to-string
 (with-output-to-sequence (*html-stream*)
   
>>))

 =>

 "

    
      
    
  
"

This is basically the same thing as Lisp's backtick reader (which is for list quasi quoting), but it also works for various other things like XML (installed on a special <> syntax), JavaScript (installed on `js-inline), etc.

To make it clear, this is implemented in a user library! And it compiles the static XML, JavaScript, etc. parts into UTF-8 encoded literal byte arrays that are ready to be written to the network stream. With a simple , (comma) you can get back to lisp and interleave runtime generated data into the literal byte arrays.

This is not for the faint of heart, but this is what the library compiles the above into:

(progn
 (write-sequence
  #(60 100 105 118 32 99 111 110 115 116 97 110 116 65 116 116 114 105 98
    117 116 101 61 34 52 50 34 32 115 111 109 101 74 97 118 97 83 99 114
    105 112 116 61 34 106 97 118 97 115 99 114 105 112 116 58 32 112 114
    105 110 116 40 40 52 48 32 43 32 50 41 41 34 32 114 117 110 116 105
    109 101 65 116 116 114 105 98 117 116 101 61 34)
  *html-stream*)
 (write-quasi-quoted-binary
  (let ((*transformation*
          #))
    (transform-quasi-quoted-string-to-quasi-quoted-binary
      (let ((*transformation*
               #))
        (locally
            (declare (sb-ext:muffle-conditions sb-ext:compiler-note))
         (let ((it (concatenate 'string "runtime calculated: " "&foo" "&bar")))
           (if it
               (transform-quasi-quoted-xml-to-quasi-quoted-string/attribute-value it)
               nil))))))
  *html-stream*)
 (write-sequence
  #(34 62 10 32 32 60 115 111 109 101 82 97 110 100 111 109 69 108 101 109
    101 110 116 62 10 32 32 32 32 60 115 111 109 101 79 116 104 101 114 47
    62 10 32 32 60 47 115 111 109 101 82 97 110 100 111 109 69 108 101 109
    101 110 116 62 10 60 47 100 105 118 62 10)
  *html-stream*)
 +void+)

For reference, the two big byte vectors in the above look like this when converted to string:

"

And the second one:

"\">