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v0.0.3: no untagged or mixed tagged unions anymore

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Alexander Nutz
2025-09-12 10:20:24 +02:00
parent d3d8d9a3cc
commit 5d447cb520
1 changed files with 10 additions and 10 deletions
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20
spec.md
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@@ -84,26 +84,26 @@ def example3() : User {
}
```
## mixed-tagged union types
## (tagged) union types
```
type Option[t] =
'Err Unit # Unit that has tag enum 'Err
| t # has no tag
'Err # If no type specified after tag, defaults to Unit
| 'Some t
# the tags of unions are weakly attached to the types, but won't decay unless they have to *)
# the tags of unions are weakly attached to the types, but won't decay unless they have to
def example(n: Num) : Num {
let x = 'MyTag n # type of x is 'MyTag Num
x # tag gets removed because target type is Num
}
def example2(n: Num) : Option[Num] {
n # this works, because the `t` is not tagged in option
'Some n
}
def example3-invalid() : Option[Num] {
Unit # error: can't convert type `Unit` into type `'Err Unit | t`
Unit # error: can't convert type `Unit` into type `'Err Unit | 'Some Num`
# Either label the expression with 'Err,
# or change the return type to Option[Unit]
# or change the return type to Option[Unit], and label the expression with 'Some
}
def exampe4(): Option[Num] {
@@ -116,8 +116,8 @@ def exampe4(): Option[Num] {
def example5-error(): Option[Num] {
let x = ( 'Err Unit ) :: Option[Unit]
x
# error: can't convert type `'Err Unit | Unit` into type `'Err Unit | Num`
# The case `Unit` does not exist in the target `'Err Unit | Num`
# error: can't convert type `'Err Unit | 'Some Unit` into type `'Err Unit | 'Some Num`
# The case `'Some Unit` does not exist in the target `'Err Unit | 'Some Num`
}
def example6-error(): Option[Unit] {
@@ -126,7 +126,7 @@ def example6-error(): Option[Unit] {
# in this case, the enum tag does not decay, like in `example`,
# because we are casting to an enum
# error: can't convert type `'Error Unit` into type `'Err Unit | Num``
# error: can't convert type `'Error Unit` into type `'Err Unit | 'Some Num``
# 1st possible solution: manually cast to just `Unit` (via `expr :: Unit`), so that it can convert to the second case of the target
# 2nd possible solution: pattern match against the enum, to rename the tag from 'Error to 'Err
}