Ch.hs

--Ch.hs 
module Ch (chlen,pitch) where
import Data.Complex
pitch = 12.7
p = pitch
chlen a b c = (l + f + r) * 2
    where   rf = pcr a
            rr = pcr b
            l' = rf - rr
            l = sqrt(c ** 2 - l' ** 2)
            th = atan (c / l')
            sf = sirc a / 2
            sr = sirc b / 2
            f = sf * (pi - th) / pi
            r = sr * th / pi
sirc = (p *)
rOfd = 7.8 / 2
yen = pi * 2
rd0 n | even n      = (n,round (rd d)) 
      | otherwise   = (n,round (rd' d)) 
    where d = fromIntegral n
rd n = pcd n - rOfd * 2
rd' n = let a = mkPolar m (pi/n/2) 
            b = mkPolar m pi 
        in dist a b 
        where m = pcr n-rOfd
dist a b = magnitude (a - b)
pcr n = d / sin t 
    where   d = p / 2 
            t = pi / n 
pcd n = pcr n * 2