## TOC »

## Rationale

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, which are ledal identifiers, is

- two dots: the argument to the left references a callable list with zero or one items
- three dots: the argument to the left references a callable list
- four dots: the argument to the left references a nonempty callable list

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

We've used callable lists instead of ordinary lists for ease of use. Indeed, (lst 3) is much easyer on the fingers than (list-ref lst 3).

Note, that there is an egg written by Mario, callable-data-structures, and one written by me, callable-sequences, which could have been used instead. But since we only need list arguments and their values on indexes, the only necessary routine, callable, is defined here, so that there are no dependencies.

The implementation of the macro is quite simple. I use a not so well-known Chicken extension of syntax-rules, which allows to replace the ellipsis with another symbol, here !!!. So I can use .., ... and .... as keywords.

### API

#### callable

`callable``lst`proceduremakes the list argument, lst, callable, i.e. encapsulates it in a procedure of zero or one argument. With no argument it returns the encapsulated list and with one argument, an index, returns the list's value at that index.

#### lambda*

`(lambda* (x ...) xpr . xprs)`syntaxthe first three evaluate to (lambda (x ... . xs) xpr . xprs) making xs callable and checking if xs is of length at most 1, arbitrary or at least1, respectively. The last one evaluates to ordinary (lambda (x ...) xpr . xprs)

#### dotted-lambdas

`dotted-lambdas`procedure

`dotted-lambdas``sym`procedurewith sym: documentation of exported symbol without sym: list of exported symbols

### Examples

(import dotted-lambdas) (condition-case (lst0 0) ((exn) #f)) ;-> #f (lst 0) ;-> 0 (lst 3) ;-> 3 (condition-case (lst 5) ((exn) #f)) ;-> #f (condition-case (lst -1) ((exn) #f)) ;-> #f ((lambda* (xs ...) (list (xs 0) (xs 1) (xs 2))) 1 2 3) ;-> (quote (1 2 3)) ((lambda* (x xs ...) (apply list x (xs))) 1 2 3) ;-> (quote (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))) ;-> (quote ()) ((lambda* (x y zs ...) (list x y (zs 0) (zs 1))) 1 2 3 4) ;-> (quote (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) ;-> (quote (1 2)) ((lambda* (as ...) (as)) 1 2 3) ;-> (quote (1 2 3)) ((lambda* (as ...) (as))) ;-> (quote ())

## Requirements

None

## Last update

Sep 4, 2020

## Author

Juergen Lorenz

## License

Copyright (c) 2020 , Juergen Lorenz, ju (at) jugilo (dot) de All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

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## Version history

- 1.0
- Initial check in