Something like a programming language for composing graphics? Racket comes awfully close to that ideal.

http://docs.racket-lang.org/quick/index.html

I laid out a conference poster this way.

The poster: http://temp.sneakygcr.net/cvpr2012-mughunt-demo-poster.pdf

The source: https://gist.github.com/gcr/9854495#file-poster-rkt-L227

Unfortunately I gave in and made the center figure in Inkscape.