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Lambda - The Ultimate Imperative

Guy Lewis Steele Jr. and Gerald Jay Sussman

Discussion led by Andrew K. Hirsch on June 12, 2017

We demonstrate how to model the following common programming constructs in terms of an applicative order language similar to LISP:

  • Simple Recursion
  • Iteration
  • Compound Statements and Expressions
  • GO TO and Assignment
  • Continuation-Passing
  • Escape Expressions
  • Fluid Variables
  • Call by Name, Call by Need, and Call by Reference
The models require only (possibly self-referent) lambda application, conditionals, and (rarely) assignment. No complex data structures such as stacks are used. The models are transparent, involving only local syntactic transformations.

Some of these models, such as those for GO TO and assignment, are already well known, and appear in the work of Landin, Reynolds, and others. The models for escape expressions, fluid variables, and call by need with side effects are new. This paper is partly tutorial in intent, gathering all the models together for purposes of context.

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