Hi "Racketeers" 
,
i present the lastest feature of scheme+ for racket that allow the melting in an expression of both infix and prefix sub-expressions.
There is a disambiguating algorithm based on a finite state machine.
Note that some expression would need to be detected not only at the syntax parsing but at the execution stage.(which is not yet implemented,will be in future version).
This feature allow to get rid of use of special { } curly brackets as it is now auto-detected by scheme syntax transformers, and so you just have to use normal ( ) parenthesis.
But then you have to use a special definition procedure called define+ but i have modified in scheme+ the classic define of scheme to integrate in it the define+ special feature, still with 100% compatibility with scheme. So you rarely have to use define+.
As there is no more needs to use { } you can get rid of the use of #lang reader SRFI-105 if you just use the infix/prefix syntax, but if you want to use the indexing via [ ] yo still need the SRFI-105 parser.
Note that it could be strange to mix infix and prefix sub-expressions in an expression it is more logic to keep the same syntax in all the expression. It just could be possible because the algorithm is recursive and check the syntax for all the sub expressions, allowing the mix
Here is some concrete examples:
Note that i really prefer for infix definitions a syntax like {x := infix_expressions ...} instead of (define x infix_expressions ...)
Welcome to DrRacket, version 8.17 [cs].
Language: racket, with debugging; memory limit: 14000 MB.
> (require Scheme+)
Scheme+ v10.0 by Damien Mattei
(define x 3 * 5 + 2)
x
17
(define t 3 * (+ 2 4) - 1)
t
17
(define z (3 + 1) * (2 * (+ 2 1) - (sin 0.3)) + ((* 2 5) - 5))
z
27.817919173354642
(define x 1 + 2 + 3)
x
6
(define k 10.0 - 3.0 - 4.0 + 1 - 5.0 * 2.0 ** 3.0 / 7.0 ** 3.0)
k
3.883381924198251
(define a 7)
(define b 3)
(define r a * - b)
r
-21
(define s 3 ² + 2 · 3 · 5 + 5 ²)
s
64
(define s 3 ² + 2 * 3 * 5 + 5 ²)
s
64
And here is a simple list of examples or piece of code tested or running REPL-SRFI-105-Racket.rkt :
Welcome to DrRacket, version 8.14 [cs].
Language: reader SRFI-105, with debugging; memory limit: 8192 MB.
SRFI 105 Curly Infix for Scheme+ v9.8
SRFI-105 Curly Infix parser for Racket Scheme and R6RS by Damien MATTEI
(based on code from David A. Wheeler and Alan Manuel K. Gloria.)
Possibly skipping some header's lines containing space,tabs,new line,etc or comments.
SRFI-105.rkt : number of skipped lines (comments, spaces, directives,...) at header's beginning : 12
Parsed curly infix code result =
(module repl racket (provide (all-defined-out)) (require Scheme+))
Scheme+ v10.0 by Damien Mattei
;; examples in REPL begins here:
{3 * (+ 2 4) - 1}
17
{(- 7 (3 * (+ 2 4) - 1))}
-10
{(3 + 1) * (2 * (+ 2 1) - sin(0.3)) + ((* 2 5) - 5)}
27.817919173354642
;; the above is in prefix : (+ (* (+ 3 1) (- (* 2 (+ 2 1)) (sin 0.3))) (- (* 2 5) 5))
(define n 7)
{2 * (- n 4)}
6
(define a 3)
(define b 5)
{n + (- b a)}
9
Here is a few more syntax available in this version of Scheme+ with SRFI-105 reader:
#lang SRFI-105
(require Scheme+)
(define (foo x y) {-4 · sin(x) + x · y ² - 5 · x / y})
(foo 1.23 3.4)
8.640021262861444
{2 ³}
8
{3 · (2 ³ - 1)}
21
{(2 ³) ⁴}
4096
(define+ (chaos p q d x0 y0)
;;(define a {2 * cos{2 * pi * p / q}}) ; or {2 * (cos {2 * pi * p / q})} or {2 * cos({2 * pi * p / q})}
(define a 2 * (cos (2 * pi * p / q)))
(define+ ksx (√ ((2 + a) / 2)) ) ;; (sqrt {(2 + a) / 2})) ; or sqrt{{2 + a} / 2}
{ksy := (√ ((2 - a) / 2))} ; (sqrt {(2 - a) / 2})} ; or (define ksy (sqrt {{2 - a} / 2}))
(stream-map (lambda (z)
(match-let (((vector x y) z))
(vector ((ksx / (√ 2)) * (x + y))
{(ksy / (√ 2)) * ((- x) + y)})))
(stream-iterate (lambda (z)
(match-let (((vector x y) z))
(vector
;;((a * x) + y + (d * x) / (add1 (x ** 2))) ; infix left to right evaluation avoid extra parenthesis but is hard for humans
((a * x) + y + (d * x) / (add1 (x ²)))
(- x))))
(vector x0 y0))))
(define+ (line-length x0 y0 x1 y1)
(√ ((x1 - x0) ² + (y1 - y0) ²)))
Scheme+ and SRFI-105 reader are available on Github: