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What are free monads?

...ll x) = Roll (fmap (fmap f) x) --this is the same thing as (++) basically concatFree :: Functor f => Free f (Free f a) -> Free f a concatFree (Pure x) = x concatFree (Roll y) = Roll (fmap concatFree y) instance Functor f => Monad (Free f) where return = Pure -- just like [] x >>...
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Why do pthreads’ condition variable functions require a mutex?

...pthread_cond_wait(&cond); //imagine cond_wait did not have a mutex char *data = some_data; some_data = NULL; handle(data); } you'd naturally get a lot of race condition, what if the other thread did some_data = new_data right after you got woken up, but before you did data = some_d...
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How to drop SQL default constraint without knowing its name?

... drop the constraint and dynamically execute it. declare @schema_name nvarchar(256) declare @table_name nvarchar(256) declare @col_name nvarchar(256) declare @Command nvarchar(1000) set @schema_name = N'MySchema' set @table_name = N'Department' set @col_name = N'ModifiedDate' select @Command = '...
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Difference between 'new operator' and 'operator new'?

...ething like your own container, you can call operator new directly, like: char *x = static_cast<char *>(operator new(100)); It's also possible to overload operator new either globally, or for a specific class. IIRC, the signature is: void *operator new(size_t); Of course, if you overloa...
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Getting a list of files in a directory with a glob

...ing like that. NSMutableArray* files = [NSMutableArray array]; glob_t gt; char* pattern = "/bin/*"; if (glob(pattern, 0, NULL, &gt) == 0) { int i; for (i=0; i<gt.gl_matchc; i++) { [files addObject: [NSString stringWithCString: gt.gl_pathv[i]]]; } } globfree(&gt); retu...
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Why does String.split need pipe delimiter to be escaped?

...ring "\\|" means the regular expression '\|' which means match exactly the character '|'. share | improve this answer | follow | ...
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What does the ??!??! operator do in C?

...otnote 12 (h/t @Random832): The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set. share...
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PHP validation/regex for URL

... Some things that jump out at me: use of alternation where character classes are called for (every alternative matches exactly one character); and the replacement shouldn't have needed the outer double-quotes (they were only needed because of the pointless /e modifier on the regex). ...
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Why can't Python's raw string literals end with a single backslash?

...string; for example, r"\"" is a valid string literal consisting of two characters: a backslash and a double quote; r"\" is not a valid string literal (even a raw string cannot end in an odd number of backslashes). Specifically, a raw string cannot end in a single backslash (since the ...
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How to read a single character from the user?

Is there a way of reading one single character from the user input? For instance, they press one key at the terminal and it is returned (sort of like getch() ). I know there's a function in Windows for it, but I'd like something that is cross-platform. ...