how to make HTML from a list in scheme, racket

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This is a very long question ... I am new and joined, so please don\'t attack me. Apologies for my bad communications in English. I have some defintions:

An HTML(H) is on

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无人共我

2021-01-22 12:33

You have the right idea, but still - there are three main issues with your proposed solution:

The output will be a string, not a list, so we must append strings in the recursive steps and return strings in the base cases.
Symbols must be explicitly converted to strings if we want to concatenate them with other strings.
And last but not least: you're missing a couple of base cases, and these are essential for writing a correct solution: what should happen if the given html is an empty list? What if the first element in a list is not a symbol, but another list?

This will work, take a careful look at the things that changed:

(define (html->string html)
  (cond [(empty? html) ""]
        [(string? html) html]
        [(not (symbol? (first html)))
         (html->string (first html))]
        [else (string-append
               "<" (symbol->string (first html)) ">"
               (change-tag (rest html))
               "</" (symbol->string (first html)) ">")]))

(define (change-tag lst)
  (cond [(empty? lst) ""]
        [else (string-append
               (html->string (first lst))
               (html->string (rest lst)))]))

It works as expected:

(define html
  (list 'html
        (list 'head
              (list 'title "Hi"))
        (list 'body
              (list 'h1 "Welcome")
              "Text")))

(html->string html)
=> "<html><head><title>Hi</title></head><body><h1>Welcome</h1>Text</body></html>"

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