• Summary
• Acknowledgments
• Getting Started


• Overview of Scheme
• Lexical conventions
• Basic concepts
• Expressions
• Program structure
• Standard procedures


• Haskell Interface


• Standard Libraries
• Husk Libraries
• Standard Feature Identifiers
• Index

Proper tail recursion

Implementations of Scheme are required to be properly tail-recursive. Procedure calls that occur in certain syntactic contexts defined below are tail calls. A Scheme implementation is properly tail-recursive if it supports an unbounded number of active tail calls. A call is active if the called procedure might still return. Note that this includes calls that might be returned from either by the current continuation or by continuations captured earlier by call-with-current-continuation that are later invoked. In the absence of captured continuations, calls could return at most once and the active calls would be those that had not yet returned. A formal definition of proper tail recursion can be found in [6].