diff options
| -rw-r--r-- | ghc/docs/comm/the-beast/coding-style.html | 46 |
1 files changed, 43 insertions, 3 deletions
diff --git a/ghc/docs/comm/the-beast/coding-style.html b/ghc/docs/comm/the-beast/coding-style.html index 7f0efbf3a2..20aab896c1 100644 --- a/ghc/docs/comm/the-beast/coding-style.html +++ b/ghc/docs/comm/the-beast/coding-style.html @@ -29,9 +29,49 @@ <h2>To CPP or not to CPP?</h2> <p>We pass all the compiler sources through CPP. The - <tt>-cpp</tt> flag is always added by the build system. More - about what you're allowed to do in the way of CPP directives - later. + <tt>-cpp</tt> flag is always added by the build system. + + <p>The following CPP symbols are used throughout the compiler: + + <dl> + <dt><tt>DEBUG</tt></dt> + + <dd>Used to enables extra checks and debugging output in the + compiler. The <tt>ASSERT</tt> macro (see <tt>HsVersions.h</tt>) + provides assertions which disappear when <tt>DEBUG</tt> is not + defined. + + <p>All debugging output should be placed inside <tt>#ifdef + DEBUG</tt>; we generally use this to provide warnings about + strange cases and things that might warrant investigation. When + <tt>DEBUG</tt> is off, the compiler should normally be silent + unless something goes wrong (exception when the verbosity level + is greater than zero). + + <p>A good rule of thumb is that <tt>DEBUG</tt> shouldn't add + more than about 10-20% to the compilation time. This is the case + at the moment. If it gets too expensive, we won't use it. For + more expensive runtime checks, consider adding a flag - see for + example <tt>-dcore-lint</tt>. + </dd> + + <dt><tt>GHCI</tt></dt> + + <dd>Enables GHCi support, including the byte code generator and + interactive user interface. This isn't the default, because the + compiler needs to be bootstrapped with itself in order for GHCi + to work properly. The reason is that the byte-code compiler and + linker are quite closely tied to the runtime system, so it is + essential that GHCi is linked with the most up-to-date RTS. + Another reason is that the representation of certain datatypes + must be consistent between GHCi and its libraries, and if these + were inconsistent then disaster could follow. + </dd> + + </dl> + + <p>More about what you're allowed to do in the way of CPP + directives later. <h2>Compiler versions</h2> |