Std.Fail

Contents

import Std.Fail

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Effects

Fail

effect Fail =
    fail: fn Unit -> Never

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Functions

try

try (f: a can Fail, e): Maybe a can e

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on_fail

on_fail (f: a can Fail, e) (default: a can e): a can e

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assert

assert (cond: Bool): Unit can Fail

Fails if cond is false Note that this is the inverse of fail_if

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fail_if

fail_if (cond: Bool): Unit can Fail

Fails if cond is true Note that this is the inverse of assert

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panic_on_fail

panic_on_fail (f: a can Fail, e): a can Panic, e

Asserts the operation cannot fail. Panics at runtime if it does.

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abort_on_fail

abort_on_fail (f: a can Fail, e): a can e

Similar to panic_on_fail but aborts the entire process instead of panicking. Generally this should be avoided when possible unless you can guarantee a panic will not occur and cannot have the Panic effect in a function.

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or_panic

or_panic (f: a can Fail, e) (message: String): a can Panic, e

Panics on failure with the given error message

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ignore_fail

ignore_fail (f: a can Fail, e): Unit can e

Ignores a Fail effect, discarding it and returning Unit

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retry_until_success

retry_until_success (f: a can Fail, e): a can e

Retry a function until it succeeds (doesn’t call fail). This should be used with functions using a Fail effect along with other effects. Otherwise, it will loop forever.

get_input () -> string can IO = ...
parse (s: string) -> u32 can Fail = ...

number = retry_until_success $$
    input = get_input ()
    parse input

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