[Haskell-fr] Re: inférence

[Dupont Corentin]

 J'ai tranformé mon programme de la manière suivante (voir ci-après).
J'ai spécifié le type de la plupart des fonctions.
Ca marche mieux, mais l'écriture est sérieusement plus lourde!

J'ai encore un problème:

courbe = defaultPlotLines {
        plot_lines_values = [[ (Point a b) | (a,b) <- ps]],
        plot_lines_style = solidLine lineWidth 0 0 1
    }

donne l'erreur:
   Couldn't match expected type `Double' against inferred type `Float'
   In the first argument of `Point', namely `a'
   In the expression: (Point a b)
   In the expression: [(Point a b) | (a, b) <- ps]

en effet Point prend des doubles. Je n'ai pas trouvé de fonctions de
conversion Float vers Double...

Merci!
Corentin


*module Lagrange where*

*nombre_points :: Integer
nombre_points = 7*

*-- creation d'une liste exluant i
list :: Integer -> [Integer]
list i = filter (/=i) [0..nombre_points-1] *

*-- un terme du polynôme de Lagrange
--un_terme :: Float -> Integer -> Integer  -> Float
un_terme t j i = (t - i_f)/(j_f - i_f)
         where i_f = fromInteger i
               j_f = fromInteger j*


*--produit des termes pour obtenir le polynôme d'un point
les_termes t j = map (un_terme t j) (list j)
poly t j = product (les_termes t j)*

* *

*--blend (a,t) = a(0) * (poly t 0) + a(1) * (poly t 1) + a(2) * (poly t 2) +
a(3) * (poly t 3) +
--              a(4) * (poly t 4) + a(5) * (poly t 5) + a(6) * (poly t 6)*

*--t est le paramètre du polynôme, a sera la coordonnée (x ou y).
blend_un_point :: Float -> (Integer -> Float) -> Integer -> Float
blend_un_point t a numero_point = a(numero_point) * (poly t numero_point)
blend_les_points t a = map (blend_un_point t a) [0..6]*

*blend :: (Integer -> Float, Float) -> Float
blend (a,t) = sum (blend_les_points t a)*

*-- Sample points
xy = [(-4.0,0.0), (-1.0,1.0), (-3.0,3.0), (0.0,4.0), (3.0,3.0),(1.0,1.0),(
4.0,0.0)]*


*--creation des fonctions x et y
x :: Integer -> Float
x pos = fst (xy !! pos_Integer)
 where pos_Integer = fromInteger(pos)
y :: Integer -> Float
y pos = snd (xy !! pos_Integer)
 where pos_Integer = fromInteger(pos)*


*-- Blend the sample points for some given u:
bx :: Float -> Float
bx(u) = blend(x,u)*

*by :: Float -> Float
by(u) = blend(y,u)*

*-- Take m+1 values for u, from 0 to nombre_points, equally spaced:
us :: Integer -> [Float]
us m = map (/mf) [0..6*mf]
 where mf = fromInteger m*

*-- For*

*m = 50*

*-- we get us(m)=[0.0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1.0].*

*-- Now get a list of points for the above values of the parameter:*

*xs = map bx (us(m))
ys = map by (us(m))*


*-- Running this, we get, where I've rounded the results to 2 digits:
--
--  xs = [0.00, 0.38, 0.75, 1.1, 1.5, 1.9, 2.3, 2.6, 3.0]
--  ys = [0.00, 0.46, 1.00, 1.7, 2.3, 2.8, 3.1, 3.2, 3.0]*

*-- Finally, get a list of pairs (x,y), i.e. a list of points:*

*ps = zip xs ys*

*-- In this example, running "ps" we get, after rounding, the points:
--
-- [(0, 0), (0.38, 0.46), (0.75, 1), (1.1, 1.7),
--  (1.5, 2.3), (1.9, 2.8), (2.3, 3.1), (2.6, 3.2), (3, 3)]
--
-- Now plot lines joining these points to get an approximation of the curve
*
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