All, I started learning haskell very recently and have a question on the pattern matching style for lists. In the below snippet i.e. "(x:xs)" why do we went with round braces and not square? I know we are using cons that tells this is not a tuple but would it not make more sense to write something like [x:xs] instead of (x:xs), i thought round braces was used for pair/tuples? safeHead [] = Nothing safeHead (x:xs) = Just x Thanks, Rohit
Round braces are used for grouping, it's necessary to avoid ambiguity since
a function can be defined with more than one argument. When using case you
don't have this potential ambiguity, so don't need the parentheses. Tuples
are more of a special case in the grammar that isn't closely related to
this.
safeHead p = case p of
[] -> Nothing
x : xs -> Just x
On Friday, October 24, 2014, Rohit Sharma
All,
I started learning haskell very recently and have a question on the pattern matching style for lists.
In the below snippet i.e. "(x:xs)" why do we went with round braces and not square? I know we are using cons that tells this is not a tuple but would it not make more sense to write something like [x:xs] instead of (x:xs), i thought round braces was used for pair/tuples?
safeHead [] = Nothing safeHead (x:xs) = Just x
Thanks, Rohit
On Sat, Oct 25, 2014 at 9:01 AM, Rohit Sharma
All,
I started learning haskell very recently and have a question on the pattern matching style for lists.
In the below snippet i.e. "(x:xs)" why do we went with round braces and not square? I know we are using cons that tells this is not a tuple but would it not make more sense to write something like [x:xs] instead of (x:xs), i thought round braces was used for pair/tuples?
safeHead [] = Nothing safeHead (x:xs) = Just x
Yes this can be confusing. Lets break it into two separate questions: 1. Why [] is not used around x:xs 2. Why () is used To address 1 start ghci and try out these expressions 1: [2,3] [1:[2,3]] To address 2 try out length [1,2] ++ [3,4] and then length ([1,2] ++ [3,4]) Another related example sin pi/2 and sin (pi/2)
participants (3)
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Bob Ippolito -
Rohit Sharma -
Rustom Mody