euler: function [f, y0, a, b, h][
    [t,y]: @[a, y0]

    while [t < b][
        print [to :string .format:".3f" t, to :string .format:".3f" y]
        t: t + h
        y: y + h * call f @[t,y]
    ]
]

newtoncooling: function [ti, te]->
    (neg 0.07) * te - 20

euler 'newtoncooling 100.0 0.0 100.0 10.0