1. Rationale
    1. Usage of the functor to generate a typed options module
    2. Usage of the untyped module
    3. Generated functions of the options datatype
      1. options
      2. none
      3. some
      4. option?
      5. none?
      6. some-ref
    4. Examples
    5. Requirements
  2. Last update
  3. Author
  4. License
  5. Version History

Rationale

The option datatype is inspired by the equally named type in ML. It simply stores one or no value at all. To be able to type options, we implement it as a functor, named option-functor, and supply an untyped version as a module named options, which simply applies the functor to a module with an any? type test, i.e. no check at all. This argument module is generated implicitly by instantiation of the functor and named _options.

Usage of the functor to generate a typed options module

(require-library datatype)
(import option-functor datatype)

;; apply functor to instantiate module
(module item-options = option-functor
  (import scheme)
  (define (item? xpr) ...)
; this defines modules item-options and implicitly _item-options

;; don't forget to patch item-options.import.scm when compiling
item-options by replacing the name of the functor parameter with the
name of the functor argument _item-options

;; import the module
(import (prefix item-options item-))

;; now use the generated routines

Usage of the untyped module

(use options)

Generated functions of the options datatype

options

[procedure] (options [sym])

documentation procedure.

none

[procedure] (none)

the fundamental datatype-constructor of an empty option

some

[procedure] (some item)

the fundamental datatype-constructor for a nonempty option. In typed modules, the argument item must pass the item? check.

option?

[procedure] (option? xpr)

type predicate.

none?

[procedure] (none? xpr)

evaluates xpr to an empty option?

some-ref

[procedure] (some-ref opt)

fetches the value out of the option argument, it there is one, otherwise signals an error.

Examples

(use options)

(define opt (some 5))
(option? opt) ; -> #t
(none? opt) ; -> #f
(none? (none)) ; -> #t
(some-ref opt) ; -> 5
(option? (none)) ; -> #t
(some-ref (none)) ; -> error

Requirements

datatype

Last update

Sep 07, 2014

Author

Juergen Lorenz

License

Copyright (c) 2014, Juergen Lorenz
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.

Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
Neither the name of the author nor the names of its contributors may be
used to endorse or promote products derived from this software without
specific prior written permission. 
  
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Version History

0.2
functor renamed
0.1
initial import