[Haskell-cafe] Annoying problem when pattern matching negative integer literals and wildcards

[Viktor Dukhovni]

On Thu, Mar 14, 2019 at 10:54:58PM -0500, Vanessa McHale wrote:

> encryptionResult :: Int -> EncryptionResult
> encryptionResult 1 = HasEncryption
> encryptionResult -1 = EncryptionUnknown
> encryptionResult _ = error "Internal error."

The way I keep it straight, is that just as one must write:

	let x = encryptionResult (-1)

to evaluate "encryptionResult" at (-1), one must also write:

    encryptionResult :: Int -> EncryptionResult
    encryptionResult 1 = HasEncryption
    encryptionResult (-1) = EncryptionUnknown
    encryptionResult _ = error "Internal error."

to define the function, because binary minus takes precedence over
unary minus (which in turn takes precedence over sections, thus
(subtract 1), not (- 1)).

-- 
	Viktor.