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Lambdas with dots as symbols

Scheme lambdas allow for variable length argument lists by using a dotted list as argument list.

dotted-lambdas use ordinary lists of length at least 2 instead, whose last item is one of the symbols .., ... or ....

The meaning of theses symbols is

We've used callable instead of ordinary lists for ease of use. Indeed, (lst 3) is much easyer on the fingers than (list-ref lst 3). Moreover, they are much more flexible, because they allow for slices, e.g. (lst 2 4) and (lst 4 2).

Note, that there is an egg written by Mario, named callable-data-structures, which could have been used instead.

The implementation of the macro is quite simple. I use a Chicken extension of syntax-rules, which allows to replace ellipses with another symbol, here !!!. So I can use e.g. ... as a keyword.

API

dotted-lambdas

[procedure] (dotted-lambdas)
[procedure] (dotted-lambdas sym)

returns the list of exported symbols, if called without argument, or the documentation of sym otherwise

lambda*

[syntax] (lambda* args xpr . xprs)

a version of lambda, where args is either a lambda-list as in ordinary lambda, or a list of at least two arguments, where the last one is one of the symbols .., ... or .... and the second to last references a callable list of at most one, arbitrary many or at least one items respectively in the lambda*'s body xpr . xprs

Requirements

callables

Examples

 

(import dotted-lambdas callables (chicken condition))

((lambda* (xs ...)
   (list (xs 0) (xs 1) (xs 2))) 1 2 3)
; -> '(1 2 3)
(condition-case
  ((lambda* (xs ..) xs) 1 2 3)
  ((exn) #f))
; -> #f
(condition-case
  ((lambda* (xs ....) xs))
  ((exn) #f))
; -> #f
((lambda* (xs ...) (xs)))
; -> '()
((lambda* (x y zs ...) (list x y (zs 0) (zs 1))) 1 2 3 4)
; -> '(1 2 3 4)
(condition-case
  ((lambda* (x y zs ..) (list x y zs)) 1 2 3 4)
  ((exn) #f))
; -> #f
(condition-case
  ((lambda* (x y zs ....) (list x y zs)) 1 2)
  ((exn) #f))
; -> #f
((lambda* (a b) (list a b)) 1 2)
; -> '(1 2)
((lambda* (a b . cs) (list a b cs)) 1 2 3 4)
; -> '(1 2 (3 4))
((lambda* as as) 1 2 3)
; -> '(1 2 3)
((lambda* as as))
; -> '()

Last update

Aug 11, 2020

Author

Juergen Lorenz

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Version History
1.0 ; initial version