Earmark.Transform (Earmark v1.4.14) View Source
Transformations
Structure Conserving Transformers
For the convenience of processing the output of EarmarkParser.as_ast
we expose two structure conserving
mappers.
map_ast
takes a function that will be called for each node of the AST, where a leaf node is either a quadruple
like {"code", [{"class", "inline"}], ["some code"], %{}}
or a text leaf like "some code"
The result of the function call must be
for nodes → a quadruple of which the third element will be ignored -- that might change in future, and will therefore classically be
nil
. The other elements replace the nodefor strings → strings
A third parameter ignore_strings
which defaults to false
can be used to avoid invocation of the mapper
function for text nodes
As an example let us transform an ast to have symbol keys
iex(0)> input = [
...(0)> {"h1", [], ["Hello"], %{title: true}},
...(0)> {"ul", [], [{"li", [], ["alpha"], %{}}, {"li", [], ["beta"], %{}}], %{}}]
...(0)> map_ast(input, fn {t, a, _, m} -> {String.to_atom(t), a, nil, m} end, true)
[ {:h1, [], ["Hello"], %{title: true}},
{:ul, [], [{:li, [], ["alpha"], %{}}, {:li, [], ["beta"], %{}}], %{}} ]
N.B. If this returning convention is not respected map_ast
might not complain, but the resulting
transformation might not be suitable for Earmark.Transform.transform
anymore. From this follows that
any function passed in as value of the postprocessor:
option must obey to these conventions.
map_ast_with
this is like map_ast
but like a reducer an accumulator can also be passed through.
For that reason the function is called with two arguments, the first element being the same value
as in map_ast
and the second the accumulator. The return values need to be equally augmented
tuples.
A simple example, annotating traversal order in the meta map's :count
key, as we are not
interested in text nodes we use the fourth parameter ignore_strings
which defaults to false
iex(0)> input = [
...(0)> {"ul", [], [{"li", [], ["one"], %{}}, {"li", [], ["two"], %{}}], %{}},
...(0)> {"p", [], ["hello"], %{}}]
...(0)> counter = fn {t, a, _, m}, c -> {{t, a, nil, Map.put(m, :count, c)}, c+1} end
...(0)> map_ast_with(input, 0, counter, true)
{[ {"ul", [], [{"li", [], ["one"], %{count: 1}}, {"li", [], ["two"], %{count: 2}}], %{count: 0}},
{"p", [], ["hello"], %{count: 3}}], 4}
Structure Modifying Transformers
For structure modifications a tree traversal is needed and no clear pattern of how to assist this task with tools has emerged yet.
Link to this section Summary
Link to this section Functions
Coming soon
Coming soon