Re: [PATCH] add SRFI-119 / language/wisp to Guile? (new patch with more tests, squashed)

[Dr. Arne Babenhauserheide]

Hi,

I realized that I did not actually send the reply to the list.

Damien Mattei <damien.mattei@gmail.com> writes:

> where is the doc of Wisp? i did not yet install it, as i understand it will 
> be included in next release of Guile? 

The documentation is either in the SRFI or on the wisp website:
- https://srfi.schemers.org/srfi-119/srfi-119.html
- https://www.draketo.de/software/wisp
- https://www.draketo.de/software/wisp#after-updates

If that’s useful, I’ll gladly send a patch to add it to the Guile
reference manual.

> what is the exact meaning of : and . ?

These control how parentheses are added to turn wisp with indentation
into regular Scheme.


In general every non-empty line opens a paren-pair which closes before
the next line with lower or equal indentation:

hello world

is

(hello world)

hello
  append world "!"
newline

is

(hello
  (append world "!"))
(newline)


If you start the line with ., it does not start with a paren.

+ 1
  . 2 3

is

(+ 1
   2 3)


If you need double-parentheses, you mark one line with :
(only whitespace, one :, and comments)

let
  :
    a 1
    b 2
  + a b

is

(let
  (
    (a 1)
    (b 2))
  (+ a b))


If : is in a line with other non-whitespace non-comments, it starts an
inline paren-pair that ends at the end of the line.

define : hello world
  display "Hello "
  display world

is

(define (hello world)
  (display "Hello ")
  (display world))


That can also make let look nicer:

let
  : a 1
    b 2
  + a b

is

(let
  ((a 1)
   (b 2))
  (+ a b))


> any simple examples?


  display "Hello World!"  ↦  (display "Hello World!")

  define : factorial n    ↦  (define (factorial n)            
      if : zero? n              (if (zero? n)                
         . 1                        1                      
         * n : factorial {n - 1}    (* n (factorial {n - 1}))))


> is it possible in Wisp to use normal scheme expression? can we mix the
> scheme code and wisp code?

you can use normal scheme in wisp. Within parentheses,
indentation-processing is then disabled (so you can simply copy-paste
scheme into wisp).

For example this is valid Wisp:


define (hello world)
  display (string-append "Hello "
    world "!")
  newline
  
hello "Wisp"


The reason is that the goal of wisp is to live within a Scheme world,
not replace Scheme. So the design assumes that the dominant language
will be Scheme.


The hardest part I see with such embedding is to stay simple. Every
syntax adaption is a risk.

That’s the main reason why Wisp split off from readable (srfi-110):
readable added more and more special cases and lost the simplicity I see
as one of the big strength of Scheme.

Wisp in contrast is intentionally limited to the minimum set of
additions needed to create a usable indentation-based Scheme.

For example the dot-prefix (.) does not take away existing syntax
because the dot is used in a position where it is illegal in regular
Scheme: (. 1 2 3) is a syntax error. But in many Schemes, (= 1 (. 1)).


Best wishes,
Arne
-- 
Unpolitisch sein
heißt politisch sein,
ohne es zu merken.
draketo.de

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