This section describes iteration tools that are based on the idea of a "template". This is a generalization of an instruction list or an expression list in which "slots" are provided for the tool to insert varying data. Three different forms of template can be used: explicit-slot templates, named-procedure templates, and named-slot templates.
These iteration tools are extended versions of the ones in Appendix B of the book Computer Science Logo Style, Volume 3: Advanced Topics by Brian Harvey [MIT Press, 1987]. The extensions are primarily to allow for variable numbers of inputs.