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author
Louis Pilfold
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(Aug 27, 2024, 3:02 PM +0100)
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docs/runtime-errors.md
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docs/runtime-errors.md
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# Runtime errors
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There are several runtime errors that Gleam code can throw. This documentation
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lists them and their runtime properties.
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On Erlang runtime errors are Erlang maps thrown with `erlang:error/1`, having at
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least these properties:
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| Key | Type | Value |
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| --- | ---- | ----- |
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| gleam_error | Atom | See individual errors |
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| message | String | See individual errors |
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| module | String | The module the error occured in |
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| function | String | The function the error occured in |
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| line | Int | The line number the error occured on |
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On JavaScript runtime errors are instances of the JavaScript `Error` class,
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having at least these properties added to them:
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| Key | Type | Value |
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| --- | ---- | ----- |
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| gleam_error | String | See individual errors |
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| message | String | See individual errors |
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| module | String | The module the error occured in |
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| function | String | The function the error occured in |
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| line | Number | The line number the error occured on |
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## Todo
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A panic that indicates that the code has not yet been completed, intended for
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use in development.
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```gleam
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todo
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todo as "some message"
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```
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| Key | Erlang Value | JavaScript Value |
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| --- | ------------ | ---------------- |
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| gleam_error | `todo` | `"todo"` |
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| message | The given message | The given message |
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## Panic
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An explicit panic to unconditionally error.
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```gleam
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panic
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panic as "some message"
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```
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| Key | Erlang Value | JavaScript Value |
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| --- | ------------ | ---------------- |
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| gleam_error | `panic` | `"panic"` |
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| message | The given message | The given message |
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## Let assert
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An inexhaustive pattern match, erroring if the pattern does not match.
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```gleam
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let assert Ok(x) = something()
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```
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| Key | Erlang Value | JavaScript Value |
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| --- | ------------ | ---------------- |
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| gleam_error | `let_assert` | `"let_assert"` |
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| message | The given message | The given message |
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| value | The unmatched value | The unmatched value |