Using with to Compose Uncertain Structures

Let’s learn how to use the with function to help us in carrying out pattern matching.

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The logic of using with

The philosophy of with is simple. It allows us to specify pattern matches at each step of composition:

  • If the match succeeds, the composition proceeds.

  • If it fails, the composition halts and falls through to an else condition.

Here’s an example from later in this chapter:

  • We will build an API layer that has to validate data.

  • The functions will have to have unappealing if-then logic rather than simple compositions.

  • We’ll use with to smooth out the rough edges.

Here’s how the approach works. First, let’s say we’re building a new quiz with data provided by the user. We want to pass validated data to a service that stores quizzes like this:

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