1980 · Languages & software

Making a program’s promises explicit

Specifications and disciplined design connect instructions with their meaning.

Tony Hoare

1980Turing Award

Visual guide

The prize, pictured

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Making a program’s promises explicit: Specifications and disciplined design connect instructions with their meaning. — Original AI-generated infographic by Curionode. Read the text version below for the full explanation.

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Require
State the precondition.
Execute
Apply a program command.
Guarantee
Establish the postcondition.

Explicit contracts make it easier to understand how components fit together and what a correct implementation must preserve.

A correct proof of the wrong specification still produces the wrong system for its users.

01 · The idea

In everyday language

Tony Hoare developed fundamental ideas in programming languages and program reasoning. Hoare logic relates a command to a condition before it runs and a condition afterwards. His work also includes Quicksort and models of communicating processes. The award recognised a wide contribution to defining and developing programming.

Why it matters

Explicit contracts make it easier to understand how components fit together and what a correct implementation must preserve.

02 · The people

Who brought the idea to life?

Tony Hoare

Tony Hoare developed ideas that made programs both faster and easier to reason about. He invented Quicksort and introduced a logic for expressing what must hold before and after a program runs. His later work on communicating sequential processes provided a framework for concurrent systems. At Oxford he combined language design, formal specification, and verification in a sustained effort to improve software reliability.

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03 · Read further