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;;; Copyright 2024 Peter McGoron
;;; Licensed under the Apache License, Version 2.0 (the "License");
;;; you may not use this file except in compliance with the License.
;;; You may obtain a copy of the License at
;;;
;;; http://www.apache.org/licenses/LICENSE-2.0
;;;
;;; Unless required by applicable law or agreed to in writing, software
;;; distributed under the License is distributed on an "AS IS" BASIS,
;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
;;; implied. See the License for the specific language governing
;;; permissions and limitations under the License.
;;;
;;; Example of COND-VALUES using units.
(load "cond-values.scm")
(define *si-prefixes*
'((quetta . #e1e30)
(ronna . #e1e27)
(yotta . #e1e24)
(zetta . #e1e21)
(exa . #e1e18)
(peta . #e1e15)
(tera . #e1e12)
(giga . #e1e9)
(mega . #e1e6)
(kilo . #e1e3)
(hecto . #e1e2)
(deka . #e1e1)
(deci . #e1e-1)
(centi . #e1e-2)
(milli . #e1e-3)
(micro . #e1e-6)
(nano . #e1e-9)
(pico . #e1e-12)
(femto . #e1e-15)
(atto . #e1e-18)
(zepto . #e1e-21)
(yocto . #e1e-24)
(ronto . #e1e-27)
(quecto . #e1e-30)))
(define *si-algebra*
`((/ . ,/)
(* . ,*)))
(define (atom-d unit)
(after ((when (or (symbol? unit)
(and (number? unit) (exact? unit)))))
unit))
(define (prefixed-d unit)
(after ((let (length* unit 2) => (head unit))
(let (assq-d head *si-prefixes*) => (factor)))
(values factor unit)))
(define (power-d unit)
(after ((let (length* unit 3) => (head number unit))
(when (eq? head '^)))
(values number unit)))
(define (algebra-function-d unit)
(after ((let (length-at-least unit 3) => (head . rest))
(let (assq-d head *si-algebra*) => (procedure)))
(values head procedure rest)))
(define (remove-prefixes unit)
(cond-values
(after ((let (atom-d unit) => (unit)))
(values 1 unit))
;;
(after ((let (prefixed-d unit) => (factor unit)))
(let-values (((sub-factor unit-w/o-factors)
(remove-prefixes unit)))
(values (* sub-factor factor) unit-w/o-factors)))
;;
(after ((let (power-d unit) => (power unit)))
(let-values (((sub-factor sub-unit)
(remove-prefixes unit)))
(values (expt sub-factor power)
(list '^ power sub-unit))))
;;
(after ((let (algebra-function-d unit) => (head proc units)))
(let-values (((factors units)
(map-values remove-prefixes units)))
(values (apply proc factors)
(cons head units))))
(else (error "invalid unit" unit))))
(remove-prefixes '(/ (* (centi meter) (centi meter))
volt
second))
(remove-prefixes '(/ (^ 2 (centi meter))
volt
second))
(define (make-unit-destructor atom prefixed power algebra-function on-else)
(lambda (unit)
(cond-values
(apply-after (atom-d unit) atom)
(apply-after (prefixed-d unit) prefixed)
(apply-after (power-d unit) power)
(apply-after (algebra-function-d unit) algebra-function)
(else (on-else unit)))))
(import r7rs)
(define (remove-prefixes unit)
(define (on-atom unit)
(values 1 unit))
(define (on-prefixed prefix-factor unit)
(let-values (((sub-prefix sub-unit) (remove-prefixes unit)))
(values (* prefix-factor sub-prefix) sub-unit)))
(define (on-power power unit)
(let-values (((sub-prefix sub-unit) (remove-prefixes unit)))
(values (expt sub-prefix power) sub-unit)))
(define (on-algebra-function symbol procedure units)
(let-values (((prefixes units) (map-values remove-prefixes units)))
(values (apply procedure prefixes)
(cons symbol units))))
(define (on-else unit)
(error "invalid unit" 'remove-prefixes unit))
(define remove-prefixes
(make-unit-destructor on-atom
on-prefixed
on-power
on-algebra-function))
(remove-prefixes unit))
(define remove-prefixes-destructors '())
(define remove-prefixes-handlers '())
(define (add-remove-prefixes-handler destructor handler)
(set! remove-prefixes-destructors
(cons destructor remove-prefixes-destructors))
(set! remove-prefixes-handlers
(cons handler remove-prefixes-handlers)))
(define (remove-prefixes unit)
(cond-values
(any-values (lambda (destructor handler)
(apply-after (destructor unit) handler))
remove-prefixes-destructors
remove-prefixes-handlers)
(else (error "invalid unit" unit))))
(add-remove-prefixes-handler atom-d (lambda (unit)
(values 1 unit)))
(remove-prefixes 'gram)
(remove-prefixes '(kilo gram))
(add-remove-prefixes-handler prefixed-d
(lambda (factor unit)
(let-values (((sub-factor sub-unit)
(remove-prefixes unit)))
(values (* factor sub-factor) sub-unit))))
(add-remove-prefixes-handler
algebra-function-d
(lambda (head procedure units)
(let-values (((factors units) (map-values remove-prefixes units)))
(values (apply procedure factors)
(cons head units)))))
(remove-prefixes '(/ (kilo meter) (micro second)))
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