SRFI 156: Syntactic combiners for binary predicates

by Panicz Maciej Godek

status: final (2017/12/18)

See also SRFI 26: Notation for Specializing Parameters without Currying.

Abstract

Recognizing binary predicates as a specific area in which the use of prefix operators is an impediment, we propose a thin layer of "syntactic stevia" for in-fixing such predicates. It can be implemented using regular Scheme macros. We suggest that the code (is x < y) should be transformed to (< x y), and (is x < y <= z) -- to (let ((y* y)) (and (< x y*) (<= y* z))). In addition, we suggest special meaning to the _ symbol: (is _ < y) and (is x < _) should be transformed to (lambda (_) (< _ y)) and (lambda (_) (< x _)), respectively. This SRFI document also describes some other uses of the is macro and its limitations.