Automa is a regex-to-Julia compiler. By compiling regex to Julia code in the form of Expr objects, Automa provides facilities to create efficient and robust regex-based lexers, tokenizers and parsers using Julia's metaprogramming capabilities. You can view Automa as a regex engine that can insert arbitrary Julia code into its input matching process, which will be executed when certain parts of the regex matches an input.

Schema of Automa.jl

Automa.jl is designed to generate very efficient code to scan large text data, which is often much faster than handcrafted code.

Where to start

If you're not familiar with regex engines, start by reading the theory section, then you might want to read every section from the top. They're structured like a tutorial, beginning from the simplest use of Automa and moving to more advanced uses.

If you like to dive straight in, you might want to start by reading the examples below, then go through the examples in the examples/ directory in the Automa repository.


Validate some text is composed only of ASCII alphanumeric characters

generate_buffer_validator(:validate_alphanumeric, re"[a-zA-Z0-9]*") |> eval

for s in ["abc", "aU81m", "!,>"]
    println("$s is alphanumeric? $(isnothing(validate_alphanumeric(s)))")

Making a lexer

tokens = [
    :identifier => re"[A-Za-z_][0-9A-Za-z_!]*",
    :lparens => re"\(",
    :rparens => re"\)",
    :comma => re",",
    :quot => re"\"",
    :space => re"[\t\f ]+",
@eval @enum Token errortoken $(first.(tokens)...)
    [Token(i) => j for (i,j) in enumerate(last.(tokens))]
)) |> eval

collect(tokenize(Token, """(alpha, "beta15")"""))

Make a simple TSV file parser

machine = let
    name = onexit!(onenter!(re"[^\t\r\n]+", :mark), :name)
    field = onexit!(onenter!(re"[^\t\r\n]+", :mark), :field)
    nameline = name * rep('\t' * name)
    record = onexit!(field * rep('\t' * field), :record)
    compile(nameline * re"\r?\n" * record * rep(re"\r?\n" * record) * rep(re"\r?\n"))

actions = Dict(
    :mark => :(pos = p),
    :name => :(push!(headers, String(data[pos:p-1]))),
    :field => quote
        n_fields += 1
        push!(fields, String(data[pos:p-1]))
    :record => quote
        n_fields == length(headers) || error("Malformed TSV")
        n_fields = 0

@eval function parse_tsv(data)
    headers = String[]
    fields = String[]
    pos = n_fields = 0
    $(generate_code(machine, actions))
    (headers, reshape(fields, length(headers), :))

header, data = parse_tsv("a\tabc\n12\t13\r\nxyc\tz\n\n")