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author | Nadrieril | 2019-05-07 18:12:04 +0200 |
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committer | Nadrieril | 2019-05-07 18:12:04 +0200 |
commit | 3da450aa3fae23214aa982643b9bc4dd0ea4eaa6 (patch) | |
tree | 02e00cd008d2e7dc899b9211379596fe792f41c8 /dhall/src/error/text/MustMergeUnion.txt | |
parent | d8a3e831fb67f86269c4baa99f9f0798a73a7247 (diff) | |
parent | 14dfeb8e7d2aa87a361a711a485243449426b144 (diff) |
Merge branch 'reorganize'
Diffstat (limited to 'dhall/src/error/text/MustMergeUnion.txt')
-rw-r--r-- | dhall/src/error/text/MustMergeUnion.txt | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/dhall/src/error/text/MustMergeUnion.txt b/dhall/src/error/text/MustMergeUnion.txt new file mode 100644 index 0000000..68df70c --- /dev/null +++ b/dhall/src/error/text/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 |