hissp..prelude#:

(define enjoin en#X#(.join "" (map str X)))

(defun tag (tag : :* contents)
  (enjoin "<"tag">"(enjoin : :* contents)"</"!##0(.split tag)">"))

(defmacro script (: :* forms)
  `',(tag "script type='text/python'" "\n"
      (.join "\n" (map hissp.compiler..readerless forms))))

((bottle..route "/")
 O#(enjoin
    (let (s (tag "script src='https://cdn.jsdelivr.net/npm/brython@3/brython{}.js'"))
      (enjoin (.format s ".min") (.format s "_stdlib")))
    (tag "body onload='brython()'"
     (script
       (define getE X#(.getElementById browser..document X))
       (define getf@v X#(float @##'value (getE X)))
       (define set@v XY#(setattr (getE Y) 'value X))
       (attach browser..window
         : Celsius O#(-> (getf@v 'Celsius) (X#|X*1.8+32|) (set@v 'Fahrenheit))
         Fahrenheit O#(-> (getf@v 'Fahrenheit) (X#|(X-32)/1.8|) (set@v 'Celsius))))
     (let (row (enjoin (tag "input id='{0}' onkeyup='{0}()'")
                       (tag "label for='{0}'" "°{1}")))
       (enjoin (.format row "Fahrenheit" "F")"<br>"(.format row "Celsius" "C"))))))

(bottle..run : host "localhost"  port 8080  debug True)