ExAST 🔬

Search, replace, and diff Elixir code by AST pattern.

Patterns are plain Elixir — variables capture, _ is a wildcard, structs match partially, pipes are normalized. No regex, no custom DSL.

mix ex_ast.search  'IO.inspect(_)'
mix ex_ast.replace 'IO.inspect(expr, _)' 'Logger.debug(inspect(expr))' lib/
mix ex_ast.diff lib/old.ex lib/new.ex

Why

Regex can't tell IO.inspect(data) from IO.inspect(data, label: "debug"). Text diff doesn't know a function moved vs changed. ExAST works on the AST — patterns match structure, not strings.

Quick examples

# Negative literals — flag potential bugs
ExAST.Patcher.find_all(source, "Enum.take(_, -_)")

# Always-true comparisons
ExAST.Patcher.find_all(source, "{a, a}")

# Compile-time config reads
ExAST.Patcher.find_all(source, "@name Application.get_env(_, _)")

# Batch analyzer checks in one scan
ExAST.Patcher.find_many(source,
  get_env: "@_ Application.get_env(_, _)",
  dbg_call: "dbg(expr)"
)

# Specific atom values
import ExAST.Query
from("def handle_event(event, _, _) do ... end")
|> where(^event == :click or ^event == :keydown)

# Functions with transaction but no debug output
from("def _ do ... end")
|> where(contains("Repo.transaction(_)"))
|> where(not contains("IO.inspect(...)"))

Installation

def deps do
  [{:ex_ast, "~> 0.11", only: [:dev, :test], runtime: false}]
end

Documentation

What you can match

# Function calls (any arity with ...)
Enum.map(_, _)
Logger.info(...)

# Definitions
def handle_call(msg, _, state) do _ end

# Pipes (matches both forms)
Enum.map(data, f)           # also matches: data |> Enum.map(f)

# Multi-node sequences
a = Repo.get!(_, _); Repo.delete(a)

# Tuples, structs, maps
{:ok, result}
%User{role: :admin}
%{name: name}

# Directives and attributes
use GenServer
@env Application.get_env(_, _)

# Control flow
case _ do _ -> _ end
fn _ -> _ end

Code intelligence APIs

ExAST can expose advisory metadata for external indexes while remaining the semantic verifier:

import ExAST.Query

selector =
  from("def _ do ... end")
  |> where(contains("Repo.transaction(_)"))

ExAST.Index.plan(selector)
#=> %ExAST.Index.Plan{required_terms: ..., requires_source?: false}

ExAST.Symbols.definitions(source)
ExAST.Symbols.references(source)
ExAST.Comments.extract(source)

ExAST.Symbols.qualified_name({Enum, :map, 2})
#=> "Enum.map/2"

Symbols keep stable string names for indexing and expose optional mfa tuples when a BEAM module can be safely resolved.

Use these terms and facts to retrieve candidates, then verify with ExAST.Selector.find_all/3 or ExAST.Selector.match?/3.

Limitations

• No function-name wildcards — def _(_) won't match arbitrary names
• Alias expansion is syntax-aware, not semantic — no macro expansion
• Multi-node patterns require contiguous statements
• Replacement formatting uses Macro.to_string/1 — run mix format after

License

MIT