How to create cairo surface in guile

I have this code

guile> (cairo-pdf-surfac开发者_如何学运维e-create "foo.pdf" 100.0 100.0)
; and get this error
standard input:29:1: In procedure cairo-pdf-surface-create in expression (cairo-pdf-surface-create "foo.pdf" 100.0 ...):
standard input:29:1: Wrong type (expecting string): 100.0
ABORT: (wrong-type-arg)

and when I use strings as width and height

guile> (cairo-pdf-surface-create "foo.pdf" "100.0" "100.0")

Backtrace:
In standard input:
  30: 0* [cairo-pdf-surface-create "foo.pdf" {"100.0"} "100.0"]

standard input:30:1: In procedure cairo-pdf-surface-create in expression (cairo-pdf-surface-create "foo.pdf" "100.0" ...):
standard input:30:1: Wrong type (expecting real number): "100.0"

Documentation says:

cairo-pdf-surface-create (filename <char>)                                 [Function]

         (width-in-points <double>) (height-in-points <double>)

         ⇒ (ret <cairo-surface-t>)

---

At least for the most recent version, try this:

(cairo-pdf-surface-create 100.0 100.0 "foo.pdf")

See the source, which specifies the arguments in the order (sx sy filename), with the filename being optional (using the current output port if not specified).