module Interpolator;

import std.io.*;

typedef function double (double) interpolator_t;

public main(args : String[]) : int
{
    interpolator_t i1 = getInterpolator(1, 5, 4);
    interpolator_t i2 = getInterpolator(10, 2, 5);

    assert( i1(0) =~ 1 );
    assert( i1(4) =~ 5 );
    assert( i1(3) =~ 4.0 );

    assert( i2(0) =~ 10 );
    assert( i2(5) =~ 2 );
    assert( i2(1.0) =~ 8.4 );
    assert( i2(2.0) =~ 6.8 );

    return 0;
}

/*
 * Create and return a linear interpolator functor which interpolates
 * between (0.0, x1) and (sep, x2), returning the output y-value
 */
private getInterpolator(x1 : double, x2 : double, sep : double) : interpolator_t
{
    assert (sep > 0.0);

    return function double (x : double)
    {
        return x * (x2 - x1) / sep + x1;
    }
}