CODEWITHSUNDEEP
haskell
danish sodhi
danish sodhi

Reputation: 1933

Simple check in haskell

I am new to haskel.What would be a good way of doing something like this in haskell?

var1 = //can be true or false 
if(var1==true)
{
  //return someething
}
else
{
//
}

Upvotes: 0

Views: 115

Answers (2)

chi
chi

Reputation: 116174

Haskell has if-then-else conditionals.

The closest code to yours I can write is something like this:

let var = length "hello" == 5
in if var then "ok" else "no"

Note that such conditional is more similar to C or Java's var ? "ok" : "no" expression than an if()... statement, but this is to be expected since Haskell is functional, so it has no "statements", only expressions.

Any Haskell tutorial should cover this. I'd recommend you read one, if you want to learn Haskell. Trying to convert idioms from other languages is a poor strategy.

Upvotes: 3

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 477881

Haskell is a functional and declarative language. That means that usually that there is not much "do something". There is more calculate something and return it.

That may look like nitpicking, but for instance in Haskell one cannot set a variable twice: once you assign it an expression (not per se a value) , you cannot set it to a different value.

If you want to return something, you usually work with pattern matching. For instance:

f :: Bool -> String
f True = "Yes"
f False = "No"

This would be somewhat equivalent in Java/C#/... to:

public String f (boolean var1) {
    if(var1) {
        return "Yes";
    } else {
        return "No";
    }
}

Note that Haskell works lazy as well: if you return a function call or anything, you do not immediately evaluate that function call: a call is only evaluated if that is necessary.

A problem might arise how to do I/O. For that, there is the concept of an I/O monad. A monad is a functional programming technique that enforces a certain order of evaluation.

But functional programming thus requires a different "mindset" than imperative programming: you do not think of a program in terms of commands that are done one after another, but more in terms of composing functions together to generate output for a given input. Like usually a mathematician or physicist does. You compose for instance a function that, given the mass and the velocity of something, calculates the kinetic energy of that object.

Upvotes: 5

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