Computer Laboratory

Course pages 2017–18


Principal lecturer: Dr Neel Krishnaswami
Taken by: Part II
Past exam questions

No. of lectures: 12
suggested hours of supervisions: 3
Prerequisite courses: Computation Theory, Semantics of Programming Languages


The aim of this course is to show by example how type systems for programming languages can be defined and their properties developed, using techniques that were introduced in the Part IB course on Semantics of Programming Languages. The emphasis is on type systems for functional languages and their connection to constructive logic.


  • Introduction. The role of type systems in programming languages. Review of rule-based formalisation of type systems. [1 lecture]

  • ML polymorphism. ML-style polymorphism. Principal type schemes and type inference. [2 lectures]

  • Polymorphic reference types. The pitfalls of combining ML polymorphism with reference types. [1 lecture]

  • Polymorphic lambda calculus (PLC). Explicit versus implicitly typed languages. PLC syntax and reduction semantics. Examples of datatypes definable in the polymorphic lambda calculus. [3 lectures]

  • Dependent types. Dependent function types. Pure type systems. System F-omega. [2 lectures]

  • Propositions as types. Example of a non-constructive proof. The Curry-Howard correspondence between intuitionistic second-order propositional calculus and PLC. The calculus of Constructions. Inductive types. [3 lectures]


At the end of the course students should

  • be able to use a rule-based specification of a type system to carry out type checking and type inference;

  • understand by example the Curry-Howard correspondence between type systems and logics;

  • appreciate the expressive power of parametric polymorphism and dependent types.

Recommended reading

* Pierce, B.C. (2002). Types and programming languages. MIT Press.
Pierce, B. C. (Ed.) (2005). Advanced Topics in Types and Programming Languages. MIT Press.
Girard, J-Y. (tr. Taylor, P. & Lafont, Y.) (1989). Proofs and types. Cambridge University Press.