F# Data: Making structured data first-class

Accessing data in structured formats such as XML, CSV and JSON in statically typed languages is difficult, because the languages do not understand the structure of the data. Dynamically typed languages make this syntactically easier, but lead to error-prone code. Despite numerous efforts, most of the data available on the web do not come with a schema. The only information available to developers is a set of examples, such as typical server responses. We describe an inference algorithm that infers a type of structured formats including CSV, XML and JSON. The algorithm is based on finding a common supertype of types representing individual samples (or values in collections). We use the algorithm as a basis for an F# type provider that integrates the inference into the F# type system. As a result, users can access CSV, XML and JSON data in a statically-typed fashion just by specifying a representative sample document.