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Partial functions

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A partial function is a function that is not defined for all possible arguments of the specified type. Examples in the Haskell standard library are:

  • head
    ,
    tail
    : undefined for empty lists
  • (!!)
    : undefined if the index is at least as big as the list length
  • div
    : undefined if the divisor is zero

The opposite is a total function.

There are methods to avoid the use of partial functions.