:: process-keys ( g -- )
    read-keyboard keys>> :> keys
    {
        { [ key-w ] [ g 0 >>angle-diff drop ] }
        { [ key-e ] [ g 1 >>angle-diff drop ] }
        { [ key-h ] [ g [ 1 + ] change-horiz-angle drop ] }
        { [ key-l ] [ g [ 1 - ] change-horiz-angle drop ] }
    } [ [ keys nth ] dip when ] assoc-each ;