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author | Nadrieril | 2019-03-01 17:28:19 +0100 |
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committer | Nadrieril | 2019-03-01 17:28:19 +0100 |
commit | e5d9aee00b0c775df1d8e2d8819aeb80dffa73c2 (patch) | |
tree | e763a24a0d635048232e72e167ca37eafec69369 /dhall/src/errors/HandlerOutputTypeMismatch.txt | |
parent | 8a2b7536902831079eddd7b00291b718f5dd7186 (diff) |
Split abnf_to_pest and dhall into their own crates
Diffstat (limited to 'dhall/src/errors/HandlerOutputTypeMismatch.txt')
-rw-r--r-- | dhall/src/errors/HandlerOutputTypeMismatch.txt | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/dhall/src/errors/HandlerOutputTypeMismatch.txt b/dhall/src/errors/HandlerOutputTypeMismatch.txt new file mode 100644 index 0000000..f359459 --- /dev/null +++ b/dhall/src/errors/HandlerOutputTypeMismatch.txt @@ -0,0 +1,51 @@ +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 │ + └─────────────────────────────────────────────────────────────────────┘ + + +... as long as the output type of each handler function matches the declared type +of the result: + + + ┌───────────────────────────────────────────────────────────┐ + │ handlers : { Left : Natural → Bool, Right : Bool → Bool } │ + └───────────────────────────────────────────────────────────┘ + ⇧ ⇧ + These output types ... + + ... must match the declared type of the ❰merge❱ + ⇩ + ┌─────────────────────────────┐ + │ merge handlers union : Bool │ + └─────────────────────────────┘ + + +For example, the following expression is $_NOT valid: + + + ┌──────────────────────────────────────────────────────────────────────┐ + │ let union = < Left = +2 | Right : Bool > │ + │ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │ + │ in merge handlers union : Text │ + └──────────────────────────────────────────────────────────────────────┘ + ⇧ + Invalid: Doesn't match output of either handler + + +Your handler for the following alternative: + +↳ $txt0 + +... needs to return an output value of type: + +↳ $txt1 + +... but actually returns an output value of a different type: + +↳ $txt2 |