# -*- tcl -*- tcl.tk//DSL diagram//EN//1.0
proc showcorners {e corners} {
    foreach {c anchor text} $corners {
	circle radius 2 at [$e $c] \
	    color red text $text \
	    anchor $anchor 
    }
}

block {
    down
    block {
	spline right \
	    then down [1 cm] left \
	    then right
    }
    text {The spline curve ...}
}
move
block {
    down
    block {
	line dashed                   right \
	    then down [1 cm] left then right 
	spline from [last line start] right \
	    then down [1 cm] left then right 
	showcorners [last line] {
	    1 ne 1  2 nw 2  3 se 3  4 sw 4
	}
    }
    text {... with tangents displayed}
}