is there any way for multiple where statement in Haskell

Question

i tried to write 3-4 where statement in a one function but i get error and couldnt do it , i tried to do something like that :

foo x=
| x == foo1 = 5
| x == foo2 =3
| x == foo3 =1
| otherwise =2 
where foo1= samplefunct1 x
      foo2= samplefunct2 x
      foo3= samplefunct3 x

I know the code is a bit useless but i just wrote this to give an example about what i mean.

Is there anyone who can help me ? Thanks in advance.

Solution 1

Remove the = after foo x and indent your code like

foo x
    | x == foo1 = 5
    | x == foo2 =3
    | x == foo3 =1
    | otherwise =2 
    where foo1 = samplefunct1 x
          foo2 = samplefunct2 x
          foo3 = samplefunct3 x

and you're fine.

Solution 2

If your indentation is a bit uneven, like this:

foo x
 | x == foo1 = 5
 | x == foo2 =3
 | x == foo3 =1
 | otherwise =2 
 where foo1= samplefunct1 x
        foo2= samplefunct2 x
         foo3= samplefunct3 x

then indeed, the error message talks about unexpected = _{(and in the future, please do include full error message in the question body).}

You fix this error by re-aligning, or with explicit separators { ; }, making it white-space–insensitive:

foo x
 | x == foo1 = 5
 | x == foo2 =3
 | x == foo3 =1
 | otherwise =2 
 where { foo1= samplefunct1 x ;
        foo2= samplefunct2 x ;
          foo3= samplefunct3 x }

This runs fine (not that it is a nice style to use). Sometimes it even looks even to you, but isn't, if there are some tab characters hiding in the white-space.

Solution 3

This code is almost right, you just need the correct indentation: Whitespace matters in haskell. Additionally, using an = after foo is an error with guards, so you'll have to remove that as well. The result is:

foo x
  | x == foo1 = 5
  | x == foo2 =3
  | x == foo3 =1
  | otherwise =2 
  where foo1= whatever1 x
        foo2= whatever2 x
        foo3= whatever3 x

Comments

[caesar_]

thanks but i want to use 3 different functions in each where statement.As you can see from my code the first where is running with samplefunc1 and the second is running with samplefunct2 and so on, are u sure it is okey with that ?

[Daniel Gratzer]

yes, I just used id so it compiled, it doesn't matter what you stick there

[caesar_]

when i wrote someting like i get an error saying "Syntax error in input (unexpected `=') " my where statement part is |otherwise = (-1,-1) where rightk = rightCheck area number leftk = leftCheck area number and when i delete one of the where statements, it runs correctly.

[gspr]

Are you sure your whitespaces are correct? It's hard to tell what you mean by code "like" mine. What I pasted does not have syntax errors.

[gspr]

Ah, in that case, it seems your code could very well be quite different from what you pasted above. Including the actual code might help.

[caesar_]

yea i'm sure, i'll post what i wrote in my code now can you check it's where part ?

[gspr]

I can't check whitespace/indenting when your code is in a comment. Moreover, are you sure that the syntax error is not elsewhere in the code? Have you checked the line number?