CODEWITHSUNDEEP
scheme
Anandamide
Anandamide

Reputation: 243

Scheme graphics

I am using mit-scheme and its graphics library. You make a graphics device with (define device (make-graphics-device (car (enumerate-graphics-types)))) which opens up a window for graphics creation.(graphics-operation device 'set-foreground-color "black") makes the lines black. The function (graphics-operation device 'fill-polygon #(0 1 0 0 1 0 1 1)) makes a black square, every two numbers in the argument #() is a point on the shape. If I use the following: 

(define (print-cell dev x y)
  (define off .01)
  (define x+ (+ x off))
  (define x- (- x off))
  (define y+ (+ y off))
  (define y- (- y off))
  (graphics-operation dev 'fill-polygon #(x+ y+ x+ y- x- y+ x- y-)))

I get the error The object x+ passed to integer->flownum is not the correct type

I don't understand this because I can use flonums as args in the #() part of the function.

I want print-cell to take a set of coordinates and then draw a small square centered at the points such that (print-cell device .5 .5) turns into (graphics-operation device 'fill-polygon #(.51 .51 .51 .49 .49 .49 .49 .51))

Upvotes: 0

Views: 318

Answers (1)

coredump
coredump

Reputation: 38799

The #() notation reads vector constants: you are reading literal symbols, which explains why the object passed to integer->flownum is x+ and not a value bound to x+. You should think about #(x+) as being equivalent to '(x+), but for vectors. What you want to do is possible with the vector function:

(vector x+ y+ x+ y- y+ x- y-)

Upvotes: 1

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