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Lambda equivalents with dots as trailing 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

Using the appropriate dots-type gives you additional control over the length of the variable argument lists.

We've used callable-sequences 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) returning callable-sequences encapsulating '(2 3) and '(4 3) respectively.

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 not so well-known 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

callable-sequences

Examples

 

(import dotted-lambdas callable-sequences (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 14, 2020

Author

Juergen Lorenz

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Version History
1.0 ; initial version