Arrow Shapes
Arrow shapes can be specified and named using the following simple grammar. Terminals are shown in bold font and nonterminals in italics. Literal characters are given in single quotes. Square brackets [ and ] enclose optional items. Vertical bars | separate alternatives.
arrowname | : | aname [ aname [ aname [ aname ] ] ] |
aname | : | [ modifiers ] shape |
modifiers | : | [ 'o' ] [ side ] |
side | : | 'l' |
| | 'r' | |
shape | : | box |
| | crow | |
| | curve | |
| | diamond | |
| | dot | |
| | inv | |
| | none | |
| | normal | |
| | tee | |
| | vee |
The primitive shapes are:
"box" | ![]() | "crow" | ![]() | "curve" | ![]() | "diamond" | ![]() | "dot" | ![]() |
"inv" | ![]() | "none" | ![]() | "normal" | ![]() | "tee" | ![]() | "vee" | ![]() |
As for the modifiers:
- 'l'
- Clip the shape, leaving only the part to the left of the edge.
- 'r'
- Clip the shape, leaving only the part to the right of the edge.
- 'o'
- Use an open (non-filled) version of the shape.
As an example, the arrow shape lteeoldiamond is parsed as 'l' 'tee' 'o' 'l' 'diamond' and corresponds to the shape

Not all syntactically legal combinations of modifiers are meaningful or semantically valid. For example, none of the modifiers make any sense with none. The following table indicates which modifiers are allowed with which shapes.
Modifier | box | crow | diamond | dot | inv | none | normal | tee | vee |
---|---|---|---|---|---|---|---|---|---|
'l'/'r' | X | X | X | X | X | X | X | ||
'o' | X | X | X | X | X |
This yields 36 different arrow shapes. The optional second, third, fourth shapes can independently be any of the 36, but since nonenone is redundant, there are 35**4 + 35**3 + 35**2 + 35 + 1 = 1,544,761 different combinations.
The following display contains the 36 combinations possible with a single arrow shape. The node attached to the arrow is not drawn but would appear on the right side of the edge.
![]() | ![]() | ![]() | ![]() | ![]() | ![]() |
box | lbox | rbox | obox | olbox | orbox |
![]() | ![]() | ![]() | |||
crow | lcrow | rcrow | |||
![]() | ![]() | ![]() | ![]() | ![]() | ![]() |
diamond | ldiamond | rdiamond | odiamond | oldiamond | ordiamond |
![]() | ![]() | ||||
dot | odot | ||||
![]() | ![]() | ![]() | ![]() | ![]() | ![]() |
inv | linv | rinv | oinv | olinv | orinv |
![]() | |||||
none | |||||
![]() | ![]() | ![]() | ![]() | ![]() | ![]() |
normal | lnormal | rnormal | onormal | olnormal | ornormal |
![]() | ![]() | ![]() | |||
tee | ltee | rtee | |||
![]() | ![]() | ![]() | |||
vee | lvee | rvee | |||
![]() | ![]() | ![]() | |||
curve | lcurve | rcurve |
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