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author | Nadrieril | 2019-05-06 23:17:26 +0200 |
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committer | Nadrieril | 2019-05-06 23:20:47 +0200 |
commit | 60129b7d1c0ea8bdf2ec666fa51957e97465e88f (patch) | |
tree | 2118155537989a1a3bfa6c51b5c476651a0ef93e /dhall/src/error/text/MissingHandler.txt | |
parent | 423fdeebe9247b16744fae4b50df415bbd08be04 (diff) |
Consolidate errors in the error module
Diffstat (limited to 'dhall/src/error/text/MissingHandler.txt')
-rw-r--r-- | dhall/src/error/text/MissingHandler.txt | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/dhall/src/error/text/MissingHandler.txt b/dhall/src/error/text/MissingHandler.txt new file mode 100644 index 0000000..433445e --- /dev/null +++ b/dhall/src/error/text/MissingHandler.txt @@ -0,0 +1,32 @@ +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 you must provide exactly one handler per alternative in the union. You +cannot omit any handlers + +For example, the following expression is $_NOT valid: + + + Invalid: Missing ❰Right❱ handler + ⇩ + ┌─────────────────────────────────────────────────┐ + │ let handlers = { Left = Natural/even } │ + │ in let union = < Left = +2 | Right : Bool > │ + │ in merge handlers union : Bool │ + └─────────────────────────────────────────────────┘ + + +Note that you need to provide handlers for other alternatives even if those +alternatives are never used + +You need to supply the following handlers: + +↳ $txt0 |