Update EncodeDecode example for new Roc static dispatch #251
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- Replace old abilities-based encoding with new static dispatch - Demonstrate where clauses for encode_str and encode_list - Show custom type encoding with Person example - Update README with new syntax and expected output Note: This example uses new Roc syntax and will work once the examples repo is updated to new Roc.
Anton-4
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Dec 31, 2025
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Anton-4
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Anton-4
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Thanks @codegod100 :)
I would like to split this up into two examples:
- Minimal encode-decode example: Easily digestible for human brains.
- Larger, more advanced encode-decode example
Maybe we should wait with updating till we have more auto derive stuff implemented in the new compiler? That will change the code a lot.
- We should also update this to a notebook file format once that is implemented in the new compiler. That makes it easy to ensure all code in the .md file stays up-to-date.
examples/EncodeDecode/main.roc
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| # Define a Person type that can be encoded as a JSON object | ||
| Person := [Person({ name : Str, age : U64 })].{ | ||
| # Custom encode method for Person - encodes as JSON object | ||
| encode : Person, JsonFormat -> List(U8) | ||
| encode = |self, fmt| { | ||
| # Get the inner record via pattern match | ||
| match self { | ||
| Person({ name, age }) => { | ||
| # Encode name as JSON string | ||
| name_bytes = name.encode(fmt) | ||
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| # Encode age as number (no quotes) | ||
| age_bytes = Str.to_utf8(age.to_str()) | ||
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| # Build: {"name":"...","age":...} | ||
| var $result = Str.to_utf8("{\"name\":") | ||
| $result = $result.concat(name_bytes) | ||
| $result = $result.concat(Str.to_utf8(",\"age\":")) | ||
| $result = $result.concat(age_bytes) | ||
| $result = $result.concat(Str.to_utf8("}")) | ||
| $result | ||
| } | ||
| } | ||
| } | ||
| } |
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I believe this will be more auto derived in the future, can you add a TODO comment above this to make this use auto derive when it is implemented?
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This PR updates the EncodeDecode example to use the new Roc static dispatch syntax.
Changes
encode_strandencode_listmethod requirementsPersonexample showing nested encodingNote
This example uses new Roc syntax (static dispatch,
match,var, etc.) and will work once the examples repo is updated to new Roc.Based on: roc-lang/roc@22cf61f
cc @Anton-4 - migrated from roc-lang/basic-cli#415 per your suggestion