Haskell: parse error on input ‘=’ in where
I am new in Haskell and practicing Algorithm in Haskell follow the book "Pearls of Functional Algorithm Design"
This is the algo to find the smallest natural number not in a given finite set X of natural numbers
import Data.List
import Data.Array
minfree xs = if null ([0..b-1] \ us)
then head ([b..] \ vs)
else head ([0..b-1] \ us)
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
Pff the compiler error like this
Prelude Data.Array Data.List> :load 01_the_smallest_free_number.hs
[1 of 1] Compiling Main ( 01_the_smallest_free_number.hs, interpreted )
01_the_smallest_free_number.hs:11:29: error:
parse error on input ‘=’
Perhaps you need a 'let' in a 'do' block?
e.g. 'let x = 5' instead of 'x = 5'
|
11 | b = div (length xs) 2
| ^
Failed, no modules loaded.
Well obveriously add let before b is not the right answer I've tried.
Then I replaced all b to div (length xs) 2 that works, so seems here is the problem to be, but I don't get it
haskell
asked Nov 11 at 7:47
Aries_is_there
1518
add a comment |
I am new in Haskell and practicing Algorithm in Haskell follow the book "Pearls of Functional Algorithm Design"
This is the algo to find the smallest natural number not in a given finite set X of natural numbers
import Data.List
import Data.Array
minfree xs = if null ([0..b-1] \ us)
then head ([b..] \ vs)
else head ([0..b-1] \ us)
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
Pff the compiler error like this
Prelude Data.Array Data.List> :load 01_the_smallest_free_number.hs
[1 of 1] Compiling Main ( 01_the_smallest_free_number.hs, interpreted )
01_the_smallest_free_number.hs:11:29: error:
parse error on input ‘=’
Perhaps you need a 'let' in a 'do' block?
e.g. 'let x = 5' instead of 'x = 5'
|
11 | b = div (length xs) 2
| ^
Failed, no modules loaded.
Well obveriously add let before b is not the right answer I've tried.
Then I replaced all b to div (length xs) 2 that works, so seems here is the problem to be, but I don't get it
haskell
asked Nov 11 at 7:47
Aries_is_there
1518
2
Bad identation causes the problem I guess.
– Sereja Bogolubov
Nov 11 at 8:35
add a comment |
I am new in Haskell and practicing Algorithm in Haskell follow the book "Pearls of Functional Algorithm Design"
This is the algo to find the smallest natural number not in a given finite set X of natural numbers
import Data.List
import Data.Array
minfree xs = if null ([0..b-1] \ us)
then head ([b..] \ vs)
else head ([0..b-1] \ us)
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
Pff the compiler error like this
Prelude Data.Array Data.List> :load 01_the_smallest_free_number.hs
[1 of 1] Compiling Main ( 01_the_smallest_free_number.hs, interpreted )
01_the_smallest_free_number.hs:11:29: error:
parse error on input ‘=’
Perhaps you need a 'let' in a 'do' block?
e.g. 'let x = 5' instead of 'x = 5'
|
11 | b = div (length xs) 2
| ^
Failed, no modules loaded.
Well obveriously add let before b is not the right answer I've tried.
Then I replaced all b to div (length xs) 2 that works, so seems here is the problem to be, but I don't get it
haskell
asked Nov 11 at 7:47
Aries_is_there
1518
I am new in Haskell and practicing Algorithm in Haskell follow the book "Pearls of Functional Algorithm Design"
This is the algo to find the smallest natural number not in a given finite set X of natural numbers
import Data.List
import Data.Array
minfree xs = if null ([0..b-1] \ us)
then head ([b..] \ vs)
else head ([0..b-1] \ us)
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
Pff the compiler error like this
Prelude Data.Array Data.List> :load 01_the_smallest_free_number.hs
[1 of 1] Compiling Main ( 01_the_smallest_free_number.hs, interpreted )
01_the_smallest_free_number.hs:11:29: error:
parse error on input ‘=’
Perhaps you need a 'let' in a 'do' block?
e.g. 'let x = 5' instead of 'x = 5'
|
11 | b = div (length xs) 2
| ^
Failed, no modules loaded.
Well obveriously add let before b is not the right answer I've tried.
Then I replaced all b to div (length xs) 2 that works, so seems here is the problem to be, but I don't get it
haskell
haskell
asked Nov 11 at 7:47
Aries_is_there
1518
asked Nov 11 at 7:47
Aries_is_there
1518
asked Nov 11 at 7:47
Aries_is_there
1518
asked Nov 11 at 7:47
Aries_is_there
1518
asked Nov 11 at 7:47
Aries_is_there
1518
1518
2
Bad identation causes the problem I guess.
– Sereja Bogolubov
Nov 11 at 8:35
add a comment |
2
Bad identation causes the problem I guess.
– Sereja Bogolubov
Nov 11 at 8:35
2
2
Bad identation causes the problem I guess.
– Sereja Bogolubov
Nov 11 at 8:35
Bad identation causes the problem I guess.
– Sereja Bogolubov
Nov 11 at 8:35
add a comment |
1 Answer
1
active
oldest
votes
This is bad indentation:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
Since the second equality is indented more than the first, it continues the first one, as if we wrote
where (us, vs) = (partition (<b) xs) b = div (length xs) 2
triggering the error.
You instead want:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
so that both equations are indented in the same way.
answered Nov 11 at 8:04
chi
72.8k280135
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53246799%2fhaskell-parse-error-on-input-in-where%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
This is bad indentation:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
Since the second equality is indented more than the first, it continues the first one, as if we wrote
where (us, vs) = (partition (<b) xs) b = div (length xs) 2
triggering the error.
You instead want:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
so that both equations are indented in the same way.
answered Nov 11 at 8:04
chi
72.8k280135
add a comment |
This is bad indentation:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
Since the second equality is indented more than the first, it continues the first one, as if we wrote
where (us, vs) = (partition (<b) xs) b = div (length xs) 2
triggering the error.
You instead want:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
so that both equations are indented in the same way.
answered Nov 11 at 8:04
chi
72.8k280135
add a comment |
This is bad indentation:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
Since the second equality is indented more than the first, it continues the first one, as if we wrote
where (us, vs) = (partition (<b) xs) b = div (length xs) 2
triggering the error.
You instead want:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
so that both equations are indented in the same way.
answered Nov 11 at 8:04
chi
72.8k280135
This is bad indentation:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
Since the second equality is indented more than the first, it continues the first one, as if we wrote
where (us, vs) = (partition (<b) xs) b = div (length xs) 2
triggering the error.
You instead want:
where (us, vs) = (partition (<b) xs)
b = div (length xs) 2
so that both equations are indented in the same way.
answered Nov 11 at 8:04
chi
72.8k280135
answered Nov 11 at 8:04
chi
72.8k280135
answered Nov 11 at 8:04
chi
72.8k280135
answered Nov 11 at 8:04
chi
72.8k280135
72.8k280135
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53246799%2fhaskell-parse-error-on-input-in-where%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
2
Bad identation causes the problem I guess.
– Sereja Bogolubov
Nov 11 at 8:35