I have a list of hashes called hash_list . <div cl

Hi! I have a list of hashes called <code class="notrans

<a class="user-mention notranslate" data-hovercard-type="user" data-hovercard-url="/us

FWIW: you can avoid using hash tables if you only have one val

<a class="user-mention notranslate" data-hovercard-type="user" data-hovercard-url="/us

Having a hard time with maps about pollen-users HOT 4 CLOSED

jaybonthius commented on June 26, 2024

Having a hard time with maps

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Comments (4)

sorawee commented on June 26, 2024 1

Hi!

I have a list of hashes called hash_list.

Note that the code that you wrote has missing parens, and is not a list of hashes. The list of hashes probably should be:

'(#hasheq((video . "path/to/example_0000.mp4"))
  #hasheq((video . "path/to/example_0001.mp4")))

Here's my attempt:

There are two possible mistakes here.

Notice that in the output, you have (video [[src ("path/to/example_0000.mp4")]]). This doesn't make sense, because the attribute src should be associated with a string value, not a list of strings.

The fix could be done by changing video-env to consume exactly one argument instead of making it consume variadic arguments. That is, you would need to make a definition like this instead:
```
(define (video-env text)
  `(video [[src ,text]]))
```
(Notice the absence of dot. Also, people usually use - instead of _ in names)
Notice that in the output, you have ((video ...) (video ...)). This again doesn't make sense, because the body of the document should not be a list of elements. There are several ways to fix this. One possibility is:
```
(apply @ (map .......))
```

So, your final code might look like this:

;; test.html.pm
#lang pollen

◊(define hash-list
  '(#hasheq((video . "path/to/example_0000.mp4"))
    #hasheq((video . "path/to/example_0001.mp4"))))

◊(define (video-env text)
  `(video [[src ,text]]))

◊(define (root . xs)
   (apply @ (map (λ (hash) (video-env (hash-ref hash 'video))) hash-list)))

which produces test.html after raco pollen render test.html.pm

<html>
  <head><meta charset="UTF-8"/></head>
  <body>
    <video src="path/to/example_0000.mp4"></video>
    <video src="path/to/example_0001.mp4"></video>
  </body>
</html>

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jaybonthius commented on June 26, 2024

@sorawee That did the trick! Thank you so much for pointing out both errors and putting me on the right path. I'm beaming 😄

I dropped some parens in the hash lists when I wrote the question. Whoops!

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mbutterick commented on June 26, 2024

FWIW:

you can avoid using hash tables if you only have one value per record (and just use a flat list).
you can avoid defining a tag function if you just want the behavior of default-tag-function.
you can avoid using the splicing tag @ explicitly and instead use for/splice (which gathers the results of the iteration under a @ automatically)

So if you wished, you could simplify this example like so:

;; test2.html.pm
#lang pollen

◊(define videos
  '("path/to/example_0000.mp4"
    "path/to/example_0001.mp4"))

◊(for/splice ([v videos])
  (video #:src v))

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jaybonthius commented on June 26, 2024

@mbutterick My hash table comes from parsing a .json with multiple values per record, which isn't obvious from my oversimplified example. Sorry about that. But your points on default-tag-function and for/splice are taken! And thanks for giving an example, I appreciate it.

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Having a hard time with maps about pollen-users HOT 4 CLOSED

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