How to resolve the algorithm Nested templated data step by step in the Racket programming language

Published on 12 May 2024 09:40 PM
#Racket

How to resolve the algorithm Nested templated data step by step in the Racket programming language

Table of Contents

Problem Statement

A template for data is an arbitrarily nested tree of integer indices. Data payloads are given as a separate mapping, array or other simpler, flat, association of indices to individual items of data, and are strings. The idea is to create a data structure with the templates' nesting, and the payload corresponding to each index appearing at the position of each index. Answers using simple string replacement or regexp are to be avoided. The idea is to use the native, or usual implementation of lists/tuples etc of the language and to hierarchically traverse the template to generate the output. Given the following input template t and list of payloads p: The correct output should have the following structure, (although spacing and linefeeds may differ, the nesting and order should follow):

  1. Generate the output for the above template, t.
  2. Show which payloads remain unused.
  3. Give some indication/handling of indices without a payload. Show output on this page.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Nested templated data step by step in the Racket programming language

Source code in the racket programming language

#lang racket

(define current-not-found-handler
  (make-parameter (λ (idx max) (raise-range-error 'substitute-template "integer?" "" idx 0 max))))

(define ((substitute-template template) payloads)
  (define match-function
    (match-lambda
      [(? nonnegative-integer? idx) #:when (< idx (length payloads)) (list-ref payloads idx)]
      [(? nonnegative-integer? idx) ((current-not-found-handler) idx (sub1 (length payloads)))]
      [(list (app match-function substitutions) ...) substitutions]))
  (match-function template))

(module+ test
  (require rackunit)

  (define substitute-in-t (substitute-template '(((1 2)
                                                  (3 4 1)
                                                  5))))
 
  (define p '(Payload#0 Payload#1 Payload#2 Payload#3 Payload#4 Payload#5 Payload#6))

  (check-equal? (substitute-in-t p)
                '(((Payload#1 Payload#2)
                   (Payload#3 Payload#4 Payload#1)
                   Payload#5)))

  (define out-of-bounds-generating-template-substitution (substitute-template '(7)))
  
  (check-exn exn:fail:contract? (λ () (out-of-bounds-generating-template-substitution p)))

  (parameterize ((current-not-found-handler (λ (idx max) (format "?~a" idx))))
    (check-equal? (out-of-bounds-generating-template-substitution p) '("?7"))))

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