Re: [racket-users] difference in struct printing from default #:transparent versus make-constructor-style-printer

[Jeremy Siek]

Thanks Ryan!

On Thursday, September 3, 2020 at 5:47:50 AM UTC-4 rmculp...@gmail.com 
wrote:

> The Racket printer uses a separate property to determine whether a struct 
> is quotable. If you add 
>
>   #:property prop:custom-print-quotable 'never
>
> to the declarations of Int2 and Prim2, your program should produce the 
> output you expect. I'll add a note to the docs for 
> make-constructor-style-printer.
>
> Ryan
>
>
> On Wed, Sep 2, 2020 at 10:07 PM Jeremy Siek  wrote:
>
>> I'm seeing some bad behavior from make-constructor-style-printer when
>> there are lists mixed in with the structs. It seems to switch from print 
>> mode to
>> write mode when going under a list. Whereas the default printer for 
>> transparent structs gets this right. The following program demonstrates the 
>> difference/problem.
>> Any thoughts on how to get the make-constructor-style-printer to behave
>> properly?
>>
>> #lang racket
>> (require racket/struct)
>>
>> (struct Int1 (value) #:transparent)
>> (struct Prim1 (op arg*) #:transparent)
>>
>> (struct Int2 (value) #:transparent
>>   #:methods gen:custom-write
>>   [(define write-proc
>>  (make-constructor-style-printer
>>   (lambda (obj) 'Int2)
>>   (lambda (obj) (list (Int2-value obj)])
>> (struct Prim2 (op arg*) #:transparent
>>   #:methods gen:custom-write
>>   [(define write-proc
>>  (make-constructor-style-printer
>>   (lambda (obj) 'Prim2)
>>   (lambda (obj) (list (Prim2-op obj) (Prim2-arg* obj)])
>>
>> (define p1 (Prim1 '+ (list (Int1 1) (Int1 2
>> (print p1)(newline)
>>
>> (define p2 (Prim2 '+ (list (Int2 1) (Int2 2
>> (print p2)(newline)
>>
>> The output is:
>>
>> (Prim1 '+ (list (Int1 1) (Int1 2)))
>> (Prim2 '+ '(# #))
>>
>> -Jeremy
>>
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>>  
>> <https://groups.google.com/d/msgid/racket-users/bdeb1052-ea25-4dc0-8292-a13d15bf7870n%40googlegroups.com?utm_medium=email_source=footer>
>> .
>>
>

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[racket-users] difference in struct printing from default #:transparent versus make-constructor-style-printer

[Jeremy Siek]

I'm seeing some bad behavior from make-constructor-style-printer when
there are lists mixed in with the structs. It seems to switch from print 
mode to
write mode when going under a list. Whereas the default printer for 
transparent structs gets this right. The following program demonstrates the 
difference/problem.
Any thoughts on how to get the make-constructor-style-printer to behave
properly?

#lang racket
(require racket/struct)

(struct Int1 (value) #:transparent)
(struct Prim1 (op arg*) #:transparent)

(struct Int2 (value) #:transparent
  #:methods gen:custom-write
  [(define write-proc
 (make-constructor-style-printer
  (lambda (obj) 'Int2)
  (lambda (obj) (list (Int2-value obj)])
(struct Prim2 (op arg*) #:transparent
  #:methods gen:custom-write
  [(define write-proc
 (make-constructor-style-printer
  (lambda (obj) 'Prim2)
  (lambda (obj) (list (Prim2-op obj) (Prim2-arg* obj)])

(define p1 (Prim1 '+ (list (Int1 1) (Int1 2
(print p1)(newline)

(define p2 (Prim2 '+ (list (Int2 1) (Int2 2
(print p2)(newline)

The output is:

(Prim1 '+ (list (Int1 1) (Int1 2)))
(Prim2 '+ '(# #))

-Jeremy

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[racket-users] Re: Pretty Printing for ASTs represented as structs

[Jeremy Siek]

Thanks for the tip!

I found the following to work pretty well :)

#lang racket
(require racket/match)
(require racket/struct)

(struct Var (name)
   #:methods gen:custom-write
  [(define (write-proc ast port mode)
 (match ast
   [(Var x)
(write x port)]))])

(struct Num (value) 
   #:methods gen:custom-write
  [(define (write-proc ast port mode)
 (match ast
   [(Num n)
(write n port)]))])

(struct Let (var rhs body)
  #:methods gen:custom-write
  [(define write-proc
 (make-constructor-style-printer
  (lambda (obj) 'let)
  (lambda (obj) (list (unquoted-printing-string "([")
  (Let-var obj)
  (Let-rhs obj)
  (unquoted-printing-string "])\n")
  (Let-body obj)])
  
(define x (Var 'x))
(define y (Var 'y))
(define n (Num 42))
(define l (Let x n (Let y n x)))
(pretty-print l)

Produced the output:

(let ([ x 42 ])
 (let ([ y 42 ])
 x))


On Sunday, August 16, 2020 at 5:10:20 PM UTC-4 jackh...@gmail.com wrote:

> I recommend using make-constructor-style-printer 
> ,
>  
> which automates a lot of the fiddly indentation-handling you'd have to do 
> otherwise.
> On Sunday, August 16, 2020 at 1:48:50 PM UTC-7 jerem...@gmail.com wrote:
>
>>
>> Hi All,
>>
>> I'm looking into using Racket structs to represent abstract syntax trees.
>> I've gotten as far as defining gen:custom-write properties, but have not
>> yet figured out how to control indenting. Also, I'm not sure I'm just 
>> calling
>> write-string, write, and newline in my gen:custom-write methods, which I
>> suspect is not exactly correct.
>>
>> Are there some good up-to-date examples of this that I could look at?
>>
>> Thanks,
>> Jeremy
>>
>

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[racket-users] Pretty Printing for ASTs represented as structs

[Jeremy Siek]

Hi All,

I'm looking into using Racket structs to represent abstract syntax trees.
I've gotten as far as defining gen:custom-write properties, but have not
yet figured out how to control indenting. Also, I'm not sure I'm just 
calling
write-string, write, and newline in my gen:custom-write methods, which I
suspect is not exactly correct.

Are there some good up-to-date examples of this that I could look at?

Thanks,
Jeremy

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