Constructor style pretty printing

Questions & Answers
1

In HtDP, the structs are printed using the (make-XXX ...) constructor style either by default in REPL or via print. How do I get the same behavior for pretty printing?

I have been able to print values in constructor style via the pconvert library:

(require (only-in lang/htdp-intermediate-lambda
                  define-struct
                  make-posn)
         mzlib/pconvert)

(install-converting-printer)
(constructor-style-printing #t)

(define-struct game [snake foods obstacles ticks])

(define g
  (make-game "snake" (list) (list (make-posn 3 4)) 0))

g

However, the pconvert printer does not apply to pretty-print. The best I can get is

(parameterize ([print-as-expression #t])
  (pretty-print g))

but this one does not use the make-game and make-posn constructors.

2

I think the idea is that you use pconvert directly and then pretty-write the result. Something like this (building on your code above):

(define (pp x)
  (pretty-write
   (print-convert x #t)))

(parameterize ([pretty-print-columns 80])
  (pp (for/list ([i (in-range 20)]) g)))

produces this:

(list
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0)
 (make-game "snake" empty (list (posn 3 4)) 0))
3

This works great, thank you!

Starting with print-convert, I found the desired configuration:

In particular, I need to set at least these three parameters:

(parameterize ([constructor-style-printing #t]
               [add-make-prefix-to-constructor #t]
               [abbreviate-cons-as-list #t]
               [print-as-expression #f])
  (pretty-write (print-convert g)))
4

Great! I'm glad you got something sorted out.

Is this for use with the teaching languages? If it is for #lang-based language, there may be a way to get the language to cough up its printer and that might end up being more modular.

5

It's for use in the script. The teaching languages don't pretty print the values, however, so the outputs are often difficult to read.

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