The Azimuth Project
Experiments in the Fay EDSL for Javascript


An attempt at a simplest possible functional programming syntax for simulation model specification using the Fay embedded domain specific language (EDSL) and Javascript compiler.

The following code snippets are under test and might provide a basis for a first FSim.hs. They have mostly been lifted directly from other people’s code in Haskell or ported from other languages.


  • Matrix operations
  • Fourier transform (inverse missing)
  • Euler’s method
  • RK4
  • Crank-Nicholson method
  • Kalman filter
  • Circuits
  • Onsager
  • misc.


  • Ring oscillator
  • Zero-dimension energy balance model (EBM)
  • One-dimensional EBM
  • Kamp advective ocean model
  • Game of Life
  • misc.

RS Latch

Compiled Javascript from a Haskell application.

Bistable climate

Direct port of Nathan Urban’s R code</h1>

q0,c1,c2,m,sigma,tc,kappa :: Double
q0 = 342.5
c1 = 0.15
c2 = 0.7
m = 0.4
sigma = 5.6697e-8
tc = 273
kappa = 0.05

t0 :: (Fractional a, Floating a) => a
t0 = (1.9e-15)**(-1/6) -- correct
-- T0 = (1.9e-15)^(1/6) # ZG10 bug

t :: [Double]
t = [200,300,400]

main :: IO ()
main = do
  let ros = fmap ro t
      ir mu t = ri t mu
      ris = fmap (ir mu) t
  print $ zipWith (-) ros ris

-- incoming radiation
ri :: Double -> Double -> Double
ri t mu = mu * q0 * (1-alpha) where
    alpha = c1 + c2*(1-tanh(kappa*(t-tc)))/2

-- outgoing radiation
ro :: Double -> Double
ro t = sigma * g * t**4 where 
       g = 1 - m*tanh((t/t0)^6)    
-- plot outgoing radation as a function of temperature
-- plot(T, Ro(T),

xRng,yRng :: [Int]
xRng = [150..400] 
yRng = [0..630]

"Zaliapin and Ghil (2010), Fig. 4",

This code plots incoming radiation, for different fractional insolations

-- Output ==>
-- 0.5, 60.55600727363061 34.787581731296   -16.749269353373222
-- 1.0, 159.1940519573757 21.18048301470816 -254.84665487062694
-- 2.0, 725.3039876743584 579.7418534269186 -288.61758493203934

Ring oscillator

Ian Ross’s “Fun with Fay” is a literate blog post using Fay and html5 canvas and a timer to display an animated 5 ring oscillator with dynamic graphs.

This seemed like a good example to start with but is too complicated for describing simple simulations.

The stripped-out user interfaceses html5 Options for parameter values. This avoids the FF non-working html5 slider problem.

Work is in progress on the simulation function (loop step? iterate step?) and graph rendering etc.

He also has another blog post on creating a good-looking jquery slider. Unfortunately this is for the Yesod web framework and needs to be ported to Snap TBD.

[Zero-Dimension EBM]


If the code contains FFI calls then the compiler is usually invoked with:

fay --package fay-base <yourcode>.hs

If the code has a main function and you want to automatically generate an html file, the syntax is:

fay --html-wrapper <...

If you want to produce a library then:

fay --library

If you want to include a javascript file then:

fay --

I haven’t yet mastered when to use –no-ghc. The usage says:

"Don't typecheck, specify when not working with files


I find I have to use it under circumstances I don’t quite understand yet to avoid clashes with the ghc Prelude.

The resulting Javascript in each of these examples can be cut and pasted it into a text editor, saved it as

<filename>.js and run it with node.js,</filename>


` node <filename>.js