Learn Functional Programming in Haskell/

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Functions with Multiple Arguments

Functions with Multiple Arguments

Use tuples to write functions with multiple arguments and results.

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Now that we know about tuples, let’s see how we can use them in functions. In principle, there are two use cases:

  1. using tuples as the argument type of functions to write functions that take multiple parameters.
  2. using tuples as the return type of functions to write functions that have multiple results.

Tuples as arguments

Let’s write a function which computes the perimeter of a rectangle when given its two sides a and b:

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perimeter :: (Double, Double) -> Double
perimeter (a, b) = 2 * a + 2 * b
main = print (perimeter (2, 3))

In the equation of perimeter, we see a new kind of pattern: the tuple pattern (a, b). It will match any tuple and bind its values to the pattern variables a and b. We then use these variables to compute the result.

*Perimeter> perimeter (2, 3) 
10

We can also use literal or wildcard patterns inside tuple patterns. The function both checks whether both of its arguments are true:

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both :: (Bool, Bool) -> Bool
both (True, True) = True
both (_, _) = False
main = do 
  print (both (True, False))
  print (both (True, True))

Formally, a tuple pattern for the tuple type (t_1, t_2,..., t_N) has the form ...