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Today's Topics:
1. case statement (Imants Cekusins)
2. Re: case statement (Imants Cekusins)
3. Re: case statement (Daniel Trstenjak)
4. Re: case statement (Imants Cekusins)
5. Re: case statement (Daniel Trstenjak)
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Message: 1
Date: Tue, 7 Jul 2015 12:21:54 +0200
From: Imants Cekusins <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] case statement
Message-ID:
<cap1qinb6sbk8hfdo6f9casjpjyz1vmgbhfshwqircprcjfo...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
interestingly, the below test fails. May I ask:
If "case" a1 is not the same as "where" a1, what is its value?
Why does x=1 match against a1?
note: result1 indent is aligned with a1 on the previous line
------ test
module TestCase where
import Test.Hspec
main::IO()
main = hspec $ do
describe "TestCase" $ do
it "case 1 - pass" $ do
result1 1 `shouldBe` "one"
it "case 2 - fail" $ do
result1 2 `shouldBe` "two"
where a1 = 2
result1 x = case x of
a1 -> "one"
2 -> "two"
------------------------------
Message: 2
Date: Tue, 7 Jul 2015 12:28:58 +0200
From: Imants Cekusins <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] case statement
Message-ID:
<cap1qinyaxmji_g_pt9vcb5vnbphmapy1h2qfhljuau6rrru...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
ok with a small tweak I can see "case" a1 value is x:
result1 x = case x of
a1 -> trace (show a1) "one"
2 -> "two"
------------------------------
Message: 3
Date: Tue, 7 Jul 2015 12:36:04 +0200
From: Daniel Trstenjak <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] case statement
Message-ID: <20150707103604.GA13608@brick>
Content-Type: text/plain; charset=us-ascii
Hi Imants,
On Tue, Jul 07, 2015 at 12:28:58PM +0200, Imants Cekusins wrote:
> ok with a small tweak I can see "case" a1 value is x:
>
> result1 x = case x of
> a1 -> trace (show a1) "one"
> 2 -> "two"
'a1' is new variable which is always bound to the value of 'x' and this
case is always matching.
You should also get a warning for this:
Warning:
Pattern match(es) are overlapped
In a case alternative: 2 -> ...
Greetings,
Daniel
------------------------------
Message: 4
Date: Tue, 7 Jul 2015 12:46:25 +0200
From: Imants Cekusins <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] case statement
Message-ID:
<CAP1qinaBV4eTgOtsEeOu+pwxBROsNKiqLbHd4XjacDaN2=a...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
> 'a1' is new variable
Thank you Daniel!
is there a way to "freeze" outside variables into constants which can
be used as "case" statement patterns?
for example if I use "if", the below test passes.
It would be handy to use case statement instead of multiple ifs or guards
main::IO()
main = hspec $ do
describe "TestCase" $ do
it "case 1 - pass" $ do
result1 1 `shouldBe` "one"
it "case 2 - pass" $ do
result1 2 `shouldBe` "two"
where result1 x = if x == a1 then "one"
else if x == a2 then "two"
else "three"
where a1 = 1
a2 = 2
------------------------------
Message: 5
Date: Tue, 7 Jul 2015 13:51:17 +0200
From: Daniel Trstenjak <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] case statement
Message-ID: <20150707115117.GA14962@brick>
Content-Type: text/plain; charset=us-ascii
Hi Imants,
On Tue, Jul 07, 2015 at 12:46:25PM +0200, Imants Cekusins wrote:
> is there a way to "freeze" outside variables into constants which can
> be used as "case" statement patterns?
I don't think so.
> result1 x = if x == a1 then "one"
> else if x == a2 then "two"
> else "three"
> where a1 = 1
> a2 = 2
There're several other ways to solve this:
result1 1 = "one"
result1 2 = "two"
result1 _ = "three"
Or:
result1 x
| x == 1 = "one"
| x == 2 = "two"
| _ = "three"
Greetings,
Daniel
------------------------------
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