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Elixir

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require Logger
defmodule ElixirStan do
@moduledoc """
Documentation for `ElixirStan`.
"""
@doc """
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Get the version of the stanc3 executable bundled with the library.
"""
@spec stanc_version :: String.t() | {:error, String.t()}
def stanc_version() do
case System.cmd(Application.app_dir(:elixir_stan, "/priv/bin/stanc"), ["--version"]) do
{version_string, 0} -> String.trim(version_string)
{error, _} -> {:error, error}
end
end
@doc """
Computes the hash of a file used for caching.
Computes SHA256 of the file and truncates it to 8 bytes, then encodes it in a hex string.
"""
@spec hash_file(binary()) :: String.t()
def hash_file(file) when is_binary(file) do
<<hash::bitstring-size(64), _::binary>> = :crypto.hash(:sha256, file)
Base.encode16 hash
end
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@spec model_tmp_dir(Path.t()) :: binary | {:error, atom}
def model_tmp_dir(path) do
with {:ok, model_code} <- File.read(path) do
model_name = Path.basename(path, ".stan")
model_hash = hash_file(model_code)
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Path.join([
System.tmp_dir(),
"elixir_stan",
model_name <> model_hash <> String.replace(stanc_version(), " ", "_")
])
end
end
@doc """
Transpiles the model into C++ and stores it in a temporary directory.
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Temporary directory is based on `System.tmp_dir()`. An `elixir_stan` directory is created in the system temporary
directory and the model is stored in a subdirectory of that. The model directory is based on the model name, the hash
of the model code and the version of stanc used to compile it.
"""
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@spec transpile_model(Path.t()) :: :ok | {:error, any()}
def transpile_model(path) do
with {:ok, model_code} <- File.read(path) do
model_tmp_path = model_tmp_dir(path)
# Create model dir
:ok = File.mkdir_p(model_tmp_path)
model_tmp_file = Path.join(model_tmp_path, Path.basename(path))
# Write model code
:ok = File.write(model_tmp_file, model_code)
case System.cmd(Application.app_dir(:elixir_stan, "/priv/bin/stanc"), [model_tmp_file]) do
{_, 0} -> :ok
end
end
end
@doc """
Cleans the model tmp directory.
"""
@spec clean_model(Path.t()) :: :ok | {:error, String.t()}
def clean_model(path) do
model_tmp_path = model_tmp_dir(path)
# Remove model dir
case File.rm_rf(model_tmp_path) do
{:ok, _} ->
:ok
{:error, error, file} ->
Logger.error(
"Could not clean model: #{path}\n\t Error: #{:file.format_error(error)}\n\t File: #{file}"
)
{:error, :file.format_error(error)}
end
end
end