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Add a primop for regular expression pattern matching

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The function ‘builtins.match’ takes a POSIX extended regular
expression and an arbitrary string. It returns ‘null’ if the string
does not match the regular expression. Otherwise, it returns a list
containing substring matches corresponding to parenthesis groups in
the regex. The regex must match the entire string (i.e. there is an
implied "^<pat>$" around the regex).  For example:

  match "foo" "foobar" => null
  match "foo" "foo" => []
  match "f(o+)(.*)" "foooobar" => ["oooo" "bar"]
  match "(.*/)?([^/]*)" "/dir/file.nix" => ["/dir/" "file.nix"]
  match "(.*/)?([^/]*)" "file.nix" => [null "file.nix"]

The following example finds all regular files with extension .nix or
.patch underneath the current directory:

  let

    findFiles = pat: dir: concatLists (mapAttrsToList (name: type:
      if type == "directory" then
        findFiles pat (dir + "/" + name)
      else if type == "regular" && match pat name != null then
        [(dir + "/" + name)]
      else []) (readDir dir));

  in findFiles ".*\\.(nix|patch)" (toString ./.)
This commit is contained in:
Eelco Dolstra 2014-11-25 11:47:06 +01:00
parent 4e340a983f
commit 976df480c9
5 changed files with 84 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

30
src/libexpr/primops.cc
View file

@ -1430,7 +1430,34 @@ static void prim_hashString(EvalState & state, const Pos & pos, Value * * args,
string s = state.forceString(*args[1], context, pos);
mkString(v, printHash(hashString(ht, s)), context);
};
}
/* Match a regular expression against a string and return either
‘null’ or a list containing substring matches. */
static void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
Regex regex(state.forceStringNoCtx(*args[0], pos), true);
PathSet context;
string s = state.forceString(*args[1], context, pos);
Regex::Subs subs;
if (!regex.matches(s, subs)) {
mkNull(v);
return;
}
unsigned int len = subs.empty() ? 0 : subs.rbegin()->first + 1;
state.mkList(v, len);
for (unsigned int n = 0; n < len; ++n) {
auto i = subs.find(n);
if (i == subs.end())
mkNull(*(v.list.elems[n] = state.allocValue()));
else
mkString(*(v.list.elems[n] = state.allocValue()), i->second);
}
}
/*************************************************************
@ -1584,6 +1611,7 @@ void EvalState::createBaseEnv()
addPrimOp("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
addPrimOp("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
addPrimOp("__hashString", 2, prim_hashString);
addPrimOp("__match", 2, prim_match);
// Versions
addPrimOp("__parseDrvName", 1, prim_parseDrvName);