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Diffstat (limited to 'dhall/src/errors/HandlerInputTypeMismatch.txt')
| -rw-r--r-- | dhall/src/errors/HandlerInputTypeMismatch.txt | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/dhall/src/errors/HandlerInputTypeMismatch.txt b/dhall/src/errors/HandlerInputTypeMismatch.txt new file mode 100644 index 0000000..7d3525b --- /dev/null +++ b/dhall/src/errors/HandlerInputTypeMismatch.txt @@ -0,0 +1,49 @@ +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 input type of each handler function matches the type of the +corresponding alternative: + + + ┌───────────────────────────────────────────────────────────┐ + │ union : < Left : Natural | Right : Bool > │ + └───────────────────────────────────────────────────────────┘ + ⇧ ⇧ + These must match These must match + ⇩ ⇩ + ┌───────────────────────────────────────────────────────────┐ + │ handlers : { Left : Natural → Bool, Right : Bool → Bool } │ + └───────────────────────────────────────────────────────────┘ + + +For example, the following expression is $_NOT valid: + + + Invalid: Doesn't match the type of the ❰Right❱ alternative + ⇩ + ┌──────────────────────────────────────────────────────────────────────┐ + │ let handlers = { Left = Natural/even | Right = λ(x : Text) → x } │ + │ in let union = < Left = +2 | Right : Bool > │ + │ in merge handlers union : Bool │ + └──────────────────────────────────────────────────────────────────────┘ + + +Your handler for the following alternative: + +↳ $txt0 + +... needs to accept an input value of type: + +↳ $txt1 + +... but actually accepts an input value of a different type: + +↳ $txt2 |