Re: [Haskell-cafe] Re: [Haskell-beginners] map question

(-) happens to be the only prefix operator in haskell, it also an infix operator. so:

4 - 2 2 -3 -3

((-) 5) 3 -- note that in this case (-) is treated like any regular function so 5 is the first parameter 2 (5 - ) 3 2 (-5 ) -5 (flip (-) 5) 3 -2

It's a little wart brought about by the ambiguity in common mathematical syntax. If you play around in ghci you should get the hang of it pretty quick. - Job On Thu, Sep 17, 2009 at 11:08 AM, Gregory Propf wrote:

Remember that there is asymmetry between (+) and (-). The former has the commutative property and the latter does not so:

(+) 3 4 = 7

and

(+) 4 3 = 7

but

(-) 3 4 = -1

and

(-) 4 3 = 1

--- On *Thu, 9/17/09, Tom Doris * wrote:

From: Tom Doris Subject: Re: [Haskell-beginners] map question To: "Joost Kremers" Cc: beginners@haskell.org Date: Thursday, September 17, 2009, 6:06 AM

This works:

map (+ (-1)) [1,2,3,4]

2009/9/17 Joost Kremers http://mc/compose?to=joostkremers@fastmail.fm

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Hi all,

I've just started learning Haskell and while experimenting with map a bit, I ran into something I don't understand. The following commands do what I'd expect:

Prelude> map (+ 1) [1,2,3,4] [2,3,4,5] Prelude> map (* 2) [1,2,3,4] [2,4,6,8] Prelude> map (/ 2) [1,2,3,4] [0.5,1.0,1.5,2.0] Prelude> map (2 /) [1,2,3,4] [2.0,1.0,0.6666666666666666,0.5]

But I can't seem to find a way to get map to substract 1 from all members of the list. The following form is the only one that works, but it doesn't give the result I'd expect:

Prelude> map ((-) 1) [1,2,3,4] [0,-1,-2,-3]

I know I can use an anonymous function, but I'm just trying to understand the result here... I'd appreciate any hints to help me graps this.

TIA

Joost

-- Joost Kremers, PhD University of Frankfurt Institute for Cognitive Linguistics Grüneburgplatz 1 60629 Frankfurt am Main, Germany _______________________________________________ Beginners mailing list Beginners@haskell.org http://mc/compose?to=Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

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