Clojure

Clojure Goodness: Creating Union Of Sets

Posted on by  
Hubert Klein Ikkink

When we are working with sets in Clojure we can use some useful functions from the clojure.set namespace. In a previous post we learned how we can get the difference of several sets. To get the union of several input sets we use the union function of the clojure.set namespace. The function returns a new set that is the union of unique elements from the input sets. A nil value is ignored by the union function.

Continue reading →

Clojure Goodness: Keyword As Function

Posted on by  
Hubert Klein Ikkink

In Clojure functions are everywhere. In a previous post we learned that sets can be functions, but Clojure also makes keywords functions. A keyword is a symbol starting with a colon (:) and is mostly used in map entries as key symbol. The keyword as function accepts a map as single argument and returns the value for the key that equals the keyword in the map or nil if the keyword cannot be found.

Continue reading →

Clojure Goodness: Using Sets As Functions

Posted on by  
Hubert Klein Ikkink

One of the nice things in Clojure is that some data structures are also functions. For me this felt rather strange when learning Clojure (coming from Java), but it can be very powerful. A set in Clojure is also a function. The set as function accept a single argument and it return nil when the argument is not part of the set, otherwise the argument value is returned. This behaviour also makes a set as function a nice predicate to be used for example in collection functions.

Continue reading →

Clojure Goodness: Create New Function Complementing Other Function

Posted on by  
Hubert Klein Ikkink

The Clojure function complement can be used to created a new function that returns the opposite truth value of the old function. The new function accepts the same number of arguments as the old function. Also when we invoke the new function created by the complement the old function is actually invoked and the result is used as argument for the not function to return the opposite truth value. So if the original function returns false or nil the result for the new function is true.

Continue reading →

Clojure Goodness: Transforming Collection Items With Index

Posted on by  
Hubert Klein Ikkink

If we want to transform items in a collection we can use the map function. If we also want to use the index of the element in the collection in the transformation we must use the map-indexed function. We must provide a function with 2 arguments, where the first argument is the index of the element in the collection and the second argument is the element in the collection.

Continue reading →

Clojure Goodness: Repeating A Value Or Function Invocation

Posted on by  
Hubert Klein Ikkink

In Clojure we can use the repeat function to get an infinite sequence of a given value. We can pass a length argument to get a fixed size sequence of the value. Clojure also provides the repeatedly function that takes as argument a function without arguments. A infinite sequence of invocations of the function is returned. Just like with the repeat function we can pass a length argument so the returned sequence has a fixed size.

Continue reading →

Clojure Goodness: Composing Functions With comp

Posted on by  
Hubert Klein Ikkink

In Clojure we can use the comp function to create a new function based on multiple other functions. We create a new function by composing other functions. We can invoke the function that is returned from the comp function with input arguments. These arguments are applied to the right most function that was used with comp. Then the output of that function is the input for the next function.

Continue reading →

Clojure Goodness: Set Default Value For nil Function Argument With fnil

Posted on by  
Hubert Klein Ikkink

The function fnil can be used to create a new function from an existing function where we define default values for arguments that can be nil. Especially when we want to use a function that we didn’t write ourselves this can be helpful to handle nil values in a consistent way. We can prevent for example a NullPointerException by setting a default value. We can define default values for a maximum of three arguments for the original function. When we invoke the function that is returned from the fnil function any extra arguments after the first arguments are simply passed on to the original function.

Continue reading →

shadow-left