Debugging The Compiler


The compiler has the --timing flag to dump timing information collected during operation.

The output documents, in reverse chronological order, the cumulative time taken for the operation (and sub operations) to complete. Sub levels are indicated by successive repetitions of +.


The compiler logs various categories of information during operation at various levels.

Log levels are characterised by two things:

  • a dot-separated path of ever finer topics of interest e.g. scope.let
  • a natural number corresponding to the verbosity level e.g. 5

If the user asks for some logs by writing:

%logging "scope" 5

they will get all of the logs whose path starts with scope and whose verbosity level is less or equal to 5. By combining different logging directives, users can request information about everything (with a low level of details) and at the same time focus on a particular subsystem they want to get a lot of information about. For instance::

%logging 1
%logging "scope.let" 10

will deliver basic information about the various phases the compiler goes through and deliver a lot of information about scope-checking let binders.

You can set the logging level at the command line using:

--log <level>

and through the REPL using:

:log <string category> <level>

:logging <string category> <level>

The supported logging categories can be found using the command line flag:

--help logging

REPL Commands

To see more debug information from the REPL there are several options one can set.

Logging Categories
command description
:di <name> show debugging information for a name
:set showimplicits show values of implicit arguments

Compiler Flags

There are several ‘hidden’ compiler flags that can help expose Idris’ inner workings.

Logging Categories
command description
--dumpcases <file> dump case trees to the given file
--dumplifted <file> dump lambda lifted trees to the given file
--dumpanf <file> dump ANF to the given file
--dumpvmcode <file> dump VM Code to the given file
--debug-elab-check do more elaborator checks (currently conversion in LinearCheck)

Output Formats

Debug Output

Calling :di <name> dumps debugging information about the selected term. Specifically dumped are:

Debugging Information
topic description
Full Name(s) The fully qualified name of the term.
Multiplicity The terms multiplicity.
Erasable Arguments Things that are erased.
Detaggable argument types  
Specialised arguments  
Inferrable arguments  
Compiled version  
Compile time linked terms  
Runtime linked terms  
Size change graph