Chapter 23. Dialyzer

Dialyzer is a tool that will detect discrepancies in your program. It does so using a technique known as success typing analysis which has the advantage of providing no false positives. Dialyzer is able to detect type errors, dead code and more. provides a wrapper around Dialyzer.

23.1. How it works

Dialyzer requires a PLT file to work. The PLT file contains the analysis information from all applications which are not expected to change, or rarely do. These would be all the dependencies of the application or applications you are currently working on, including standard applications in Erlang/OTP itself.

Dialyzer can generate this PLT file. includes rules to automatically generate the PLT file when it is missing.

Once the PLT file is generated, Dialyzer can perform the analysis in record time.

23.2. Configuration

In a typical usage scenario, no variable needs to be set. The defaults should be enough. Do note however that the dependencies need to be set properly using the DEPS and LOCAL_DEPS variables.

The DIALYZER_PLT file indicates where the PLT file will be written to (and read from). By default this is $(PROJECT).plt in the project’s directory. Note that the DIALYZER_PLT variable is exported and is understood by Dialyzer directly.

The PLT_APPS variable can be used to add additional applications to the PLT. You can either list application names or paths to these applications. defines two variables for specifying options for the analysis: DIALYZER_DIRS and DIALYZER_OPTS. The former one defines which directories should be part of the analysis. The latter defines what extra warnings Dialyzer should report.

Note that enables the race condition warnings by default. As it can take considerably large resources to run, you may want to disable it on larger projects.

23.3. Usage

To perform an analysis, run the following command:

$ make dialyze

This will create the PLT file if it doesn’t exist.

The analysis will also be performed when you run the following command, alongside tests:

$ make check

You can use the plt target to create the PLT file if it doesn’t exist. This is normally not necessary as Dialyzer creates it automatically.

The PLT file will be removed when you run make distclean.