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author | NanoTech | 2016-12-11 23:27:36 -0600 |
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committer | NanoTech | 2017-03-10 23:48:29 -0600 |
commit | 5c00b978b0bc0c1eeb64682cba6aa338fea320bf (patch) | |
tree | d9935794062180474b5bd6a51ab1d5f4bd864a4e /src/errors/MustMergeUnion.txt | |
parent | efd52ef33c15316dbd39390d55022708488a53b8 (diff) |
Start implementing error explanations
Diffstat (limited to 'src/errors/MustMergeUnion.txt')
-rw-r--r-- | src/errors/MustMergeUnion.txt | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/src/errors/MustMergeUnion.txt b/src/errors/MustMergeUnion.txt new file mode 100644 index 0000000..68df70c --- /dev/null +++ b/src/errors/MustMergeUnion.txt @@ -0,0 +1,31 @@ +Explanation: You can ❰merge❱ the alternatives of a union using a record with one +handler per alternative, like this: + + + ┌─────────────────────────────────────────────────────────────────────┐ + │ let union = < Left = +2 | Right : Bool > │ + │ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │ + │ in merge handlers union : Bool │ + └─────────────────────────────────────────────────────────────────────┘ + + +... but the second argument to ❰merge❱ must be a union and not some other type. + +For example, the following expression is $_NOT valid: + + + ┌──────────────────────────────────────────┐ + │ let handlers = { Foo = λ(x : Bool) → x } │ + │ in merge handlers True : True │ + └──────────────────────────────────────────┘ + ⇧ + Invalid: ❰True❱ isn't a union + + +You tried to ❰merge❱ this expression: + +↳ $txt0 + +... which is not a union, but is actually a value of type: + +↳ $txt1 |