Motoko (programming language)

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The Motoko programming language is a new, modern and type safe language for developers who want to build the next generation of distributed applications to run on the Internet Computer blockchain network. Motoko is specifically designed to support the unique features of the Internet Computer and to provide a familiar yet robust programming environment. As a new language, Motoko is constantly evolving with support for new features and other improvements.[1]

The Motoko compiler, documentation, and other tooling is open source and released under the Apache 2.0 license.


Motoko development started in 2018. Its first open release was in Q3 2019[2].

Design Intent

Key design points[1]:

  1. Motoko takes inspiration from several programming languages, including Java, JavaScript, C#, Swift, Pony, ML, Haskell.
  2. Object-oriented, functional, and imperative
  3. Objects as records of members
  4. async/await for sequential programming of asynchronous messaging
  5. Structural typing with simple generics and subtyping
  6. Safe arithmetic (unbounded and checked)
  7. Non-nullable types by default
  8. JavaScript-like syntax but statically typed and sane


  1. call-by-value (like Java, C, JS, and ML; unlike Haskell and Nix)
  2. declarations are locally mutually recursive
  3. parametric, bounded polymorphism
  4. subtyping as subsumption, not coercion
  5. no dynamic casts
  6. no inheritance


  1. implemented in OCaml (leverages wasm library)
  2. simple reference interpreter
  3. less simple compiler to WebAssembly
  4. multipass with typed IR in each pass
  5. uniform representation, unboxed arithmetic
  6. two-space gc, gc between messages
  7. polymorphism by erasure