Add dot formatter (Graphviz)

[pocke]

Ref: https://qiita.com/Nabetani/items/7904651fae1f925129c7

Note: It is experimental, and Dot formatter supports limited parsers (Ripper.sexp, Parser, RubyParser, and RubyVM::AST).

This formatter displays Dot language for Graphviz.
For example:

$ rpr -p rubyvm_ast -e 'p 1 + 1' -f dot
digraph{graph [dpi=288;];
b -> ROOT
b[ label="SCOPE" shape=oval ]
c -> b
c[ label="[]" shape=box ]
d -> b
d[ label="nil" shape=box ]
e -> b
e[ label="FCALL" shape=oval ]
f -> e
f[ label=":p" shape=box ]
g -> e
g[ label="ARRAY" shape=oval ]
h -> g
h[ label="OPCALL" shape=oval ]
i -> h
i[ label="LIT" shape=oval ]
j -> i
j[ label="1" shape=box ]
k -> h
k[ label=":+" shape=box ]
l -> h
l[ label="ARRAY" shape=oval ]
m -> l
m[ label="LIT" shape=oval ]
n -> m
n[ label="1" shape=box ]
o -> l
o[ label="nil" shape=box ]
p -> g
p[ label="nil" shape=box ]
}

Convert to PNG

$ rpr -p rubyvm_ast -e 'p 1 + 1' -f dot | dot -Tpng -oast.png
$ open ast.png

[coveralls]

Coverage remained the same at 70.588% when pulling a6bec16 on dot-formatter into 56e3ad5 on master.

[coveralls]

Coverage remained the same at 70.588% when pulling a6bec16 on dot-formatter into 56e3ad5 on master.

[pocke]

Sample image for README

[pocke]

Updated the example image