Haskell Program Coverage (hpc) is a high-fidelity code coverage tool for Haskell, now in widespread use throughout the Haskell community. Hpc includes tools that instrument Haskell programs to record program coverage, run instrumented programs, and display the coverage information obtained. It is included with the standard GHC distribution.

What is Haskell Program Coverage?

Hpc is a tool-kit to record and display the code coverage of a Haskell Program. Typically coverage tools are used to determine if test suites is actually innovating parts of a program. Hpc is included with all versions of GHC since 6.8. so no extra downloading or installing is needed!

Quick Start and FAQ

I just want to start using Hpc. How do I do this?

You need a Haskell program, for example:

% cat Main.hs
main = print ("Hello, World " ++ show (const 1 2))

To compile use the ghc-6.8.1 (or later) command line option -fhpc:

% ghc -fhpc Main.hs 
[1 of 1] Compiling Main             ( Main.hs, Main.o )
Linking Main ...
% ./a.out
"Hello, World 1"
% hpc report a.out
 85% expressions used (6/7)
100% boolean coverage (0/0)
     100% guards (0/0)
     100% 'if' conditions (0/0)
     100% qualifiers (0/0)
100% alternatives used (0/0)
100% local declarations used (0/0)

How do I see my program marked up?

You run an instrumented binary, and then run hpc markup after execution. (If you have have just run the example about, there is no need to re-compile and re-run the binary; the coverage information is preserved in the file Main.tix)

% ./a.out
Writing: Main.hs.html
Writing: hpc_index.html
Writing: hpc_index_fun.html
Writing: hpc_index_alt.html
Writing: hpc_index_exp.html

Now we have a file, Main.hs.html, which looks like this

~~~~ {.orig style=”background: white; padding: 0px; margin: 0px”} 1 main = print (“Hello, World “ ++ show (const 1 2)) ~~~~

The number 1 at the start of the line is the line number, and we can see that ‘2’ is highlighted; it was never evaluated during the execution of this program. We have also generated some index files, that list all the modules in our executable. hpc_index.html{.haskell .geshifilter-haskell} looks like this.

What files are you using to collect coverage?

File Summary Location\ Contents
Example Example —— ————————————————————————————- —————– —————————————————————————————————- .tix array of ticks, on for each location in the program, one per program Main.tix,\ Tix [TixModule "Main" 123 9 [1,2,3,2,2,1,2,4], ...]{.haskell .geshifilter-haskell} a.out.tix

.mix module specific information, mapping tick number to source location, one per module .hpc/Main.mix,\ Mix Main.hs" 1182484948 51696526 8 [(1:15-1:29,ExpBox False),...]{.haskell .geshifilter-haskell} .hpc/Foo.mix