Version 6 (modified by 10 years ago) (diff) | ,
---|

# get rid of unary '-' operator

the unary '-' is a very odd case in the report and causes a lot of confusion.

to fix it we can

- make '-' part of the lexical syntax of numbers. so a '-' followed by digits is interpreted as a negative number
- get rid of all other special treatment of '-'
- people can use 'negate' if they want to negate non literals.
- the removal of n + k patterns will make this more attractive

Cons

- This does introduce a syntactic oddity, namely that
`-1`

is different from`- 1`

though syntax highlighting editors could make this distinction obvious.

- It would no longer be possible to write
`x-1`

to mean "x minus 1", instead it would mean "x applied to the literal -1", which is counter-intuitive. Also,`x - 1`

with spaces would have the "x minus 1" meaning.

- In Haskell 98, '-' is explicitly excluded from right sections, so:

Prelude> :t (- 1) (- 1) :: (Num a) => a Prelude> :t (1 -) (1 -) :: (Num a) => a -> a

If we removed special treatment of '-', then these become symmetrical again. However it seems unintuitive that

`(-x)`

is a right section of '-', but`(-1)`

is the literal -1.