<aside> 🏁 In this section, we’ll explore:

• What type checking, static typing, and dynamic typing mean.
• Why type-checking is approximate.
• What the advantages and disadvantages of type-checking are. </aside>

ML vs Racket

• ML and Racket have a lot in common as programming languages.

  • Both languages are oriented towards functional programming and provide similar support for constructs such as higher-order functions and closures.

• However, the biggest difference between the 2 languages is the presence of a type system.

  • ML has a type system while Racket does not.

  <aside> ⚠️ Note that the presence of a type system doesn’t determine whether a language is statically or dynamically typed. Whether a language is statically or dynamically typed largely depends on when their implementations assign types to variables.

  • If types are assigned before programs in the language run, the language is statically typed.
  • If types are assigned during runtime, the language is dynamically typed.

  A type system does, however, determine if a language is strongly or weakly typed (more on that later).

  </aside>

ML from a Racket perspective

• ML is like a well-defined subset of Racket.
• Given that ML has a type system, some programs that would normally be able to run on Racket would be disallowed from running in ML.
  • Depending on the situation, the restrictive type system could be a good or bad thing.
    • It could be good if the code is inherently buggy (and would eventually cause errors in languages without a type system anyway).
    • However, it could disallow programs that make sense but don’t follow ML’s type conventions.
  • Examples 1-2: Examples of programs that can run in Racket but not in ML

Racket from a ML perspective

• Racket can be seen as a particular style of ML programming.