Besides the documentation procedure, this module exports two curry procedures, @> and @<, and one macro, @@, which implements the holes mechanism. They all create partial procedures.
Holes are spezial identifiers, delimited by < and >, possibly enclosing zero or more digits. This new syntax replaces the old one, where both delimiters were bangs.
The macro @@ transforms expressions with zero or more holes into a procedure which has as many arguments as there are different holes in the expression. Moreover, the arguments are ordered according to the digits enclosed by the delimiters. For example, (@@ 5), is a thunk, because there are no holes. And (@@ (- <2> <1> <2>)) is a procedure of two arguments, <1> and <2> in this order, returning (- 20 10 20) when applied to 10 20: ((@@(- <2> <1> <2>)) 10 20) is -10.
But holes aren't restricted to flat list expressions, nested ones are accepted as well. For example, (@@ (+ 5 (* <> 2))) is a unary procedure which applied to 7 gives 19. The holes may appear in different nesting levels, which gives great flexibility.
Notice the difference of @@ to cut and cute. In the latter each pair <> accepts different arguments, whereas in the former different holes are needed.
- holes #!optional symprocedure
documentation procedure. Shows either the list of exported symbols or the documentation of sym.
- (@@ code)syntax
extracts the holes out of the argument expression, code, sorts them numerically while removing dups and considers the resulting list as the argument list of a procedure, with code as body.
Note, that (@@ xpr) is always a procedure, maybe a thunk, if there are no holes in xpr.
- @> proc #!rest headprocedure
returns a curried procedure with arguments tail, which applies proc to (append head tail)
- @< proc #!rest tailprocedure
returns a curried procedure with arguments head, which applies proc to (append head tail)
(hole-delimiters "!!") ((@> map add1) '(0 1 2)) ; -> '(1 2 3) ((@< list-ref 2) '(0 1 2 3)) ; -> 2 ((@@ 5)) ; -> 5 (((@@ (lambda (x) (- x <>))) 2) 3) ; ->1 (call-with-values (@@ (values 1 2 3)) list) ;-> '(1 2 3) ((@@ (list 1 2 (vector 3 4 <> 6))) 5) ; ->'(1 2 #(3 4 5 6)) ((@@ (list 1 2 '#(3 4 <> 6)))) ; note that the third arg of list is quoted ; hence there are no holes ; -> '(1 2 #(3 4 <> 6)) ((@@ (list (cons <2> <1>) (cons <1> <2>))) 1 2) ; -> '((2 . 1) (1 . 2))
Nov 11, 2019
Copyright (c) 2016-2019, Juergen Lorenz All rights reserved.
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- parameter hole-delimiters and read macros removed, only delimiters < and > accepted instead of bangs
- parameter hole-delimiters added accepting "<>" or "!!"
- port from chicken-4, version 1.4, with modifications