Idiom # 53: Join a list of strings

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Code

fold is the feature of choice to join elements of a set into a value of the element type. For type string, such operations are defined in feature strings. For concatenation with a separator, strings.concat sep is the operation to use.

Mathematically speaking, such an operation is called a monoid. This is why the type of the argument of fold is Monoid, while the operations declared in strings inherit from Monoid.

Since joining the elements of a list into a string using a given separator is a common operation, there is a convenience function to do this directly.

Running Example

Using fold.