lix/src/libexpr/nixexpr.cc
Eelco Dolstra 0a623a10c7 * Allow a default value in attribute selection by writing
x.y.z or default

  (as originally proposed in
  https://mail.cs.uu.nl/pipermail/nix-dev/2009-September/002989.html).

  For instance, an expression like

    stdenv.lib.attrByPath ["features" "ckSched"] false args

  can now be written as

    args.features.ckSched or false
2011-07-13 12:19:57 +00:00

327 lines
7.1 KiB
C++

#include "nixexpr.hh"
#include "derivations.hh"
#include "util.hh"
#include <cstdlib>
namespace nix {
/* Displaying abstract syntax trees. */
std::ostream & operator << (std::ostream & str, Expr & e)
{
e.show(str);
return str;
}
void Expr::show(std::ostream & str)
{
abort();
}
void ExprInt::show(std::ostream & str)
{
str << n;
}
void ExprString::show(std::ostream & str)
{
str << "\"" << s << "\""; // !!! escaping
}
void ExprPath::show(std::ostream & str)
{
str << s;
}
void ExprVar::show(std::ostream & str)
{
str << info.name;
}
void ExprSelect::show(std::ostream & str)
{
str << "(" << *e << ")." << showAttrPath(attrPath);
if (def) str << " or " << *def;
}
void ExprOpHasAttr::show(std::ostream & str)
{
str << "(" << *e << ") ? " << showAttrPath(attrPath);
}
void ExprAttrs::show(std::ostream & str)
{
if (recursive) str << "rec ";
str << "{ ";
foreach (AttrDefs::iterator, i, attrs)
if (i->second.inherited)
str << "inherit " << i->first << " " << "; ";
else
str << i->first << " = " << *i->second.e << "; ";
str << "}";
}
void ExprList::show(std::ostream & str)
{
str << "[ ";
foreach (vector<Expr *>::iterator, i, elems)
str << "(" << **i << ") ";
str << "]";
}
void ExprLambda::show(std::ostream & str)
{
str << "(";
if (matchAttrs) {
str << "{ ";
bool first = true;
foreach (Formals::Formals_::iterator, i, formals->formals) {
if (first) first = false; else str << ", ";
str << i->name;
if (i->def) str << " ? " << *i->def;
}
str << " }";
if (!arg.empty()) str << " @ ";
}
if (!arg.empty()) str << arg;
str << ": " << *body << ")";
}
void ExprLet::show(std::ostream & str)
{
str << "let ";
foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
if (i->second.inherited)
str << "inherit " << i->first << "; ";
else
str << i->first << " = " << *i->second.e << "; ";
str << "in " << *body;
}
void ExprWith::show(std::ostream & str)
{
str << "with " << *attrs << "; " << *body;
}
void ExprIf::show(std::ostream & str)
{
str << "if " << *cond << " then " << *then << " else " << *else_;
}
void ExprAssert::show(std::ostream & str)
{
str << "assert " << *cond << "; " << *body;
}
void ExprOpNot::show(std::ostream & str)
{
str << "! " << *e;
}
void ExprConcatStrings::show(std::ostream & str)
{
bool first = true;
foreach (vector<Expr *>::iterator, i, *es) {
if (first) first = false; else str << " + ";
str << **i;
}
}
std::ostream & operator << (std::ostream & str, const Pos & pos)
{
if (!pos.line)
str << "undefined position";
else
str << (format("`%1%:%2%:%3%'") % pos.file % pos.line % pos.column).str();
return str;
}
string showAttrPath(const AttrPath & attrPath)
{
string s;
foreach (AttrPath::const_iterator, i, attrPath) {
if (!s.empty()) s += '.';
s += *i;
}
return s;
}
Pos noPos;
/* Computing levels/displacements for variables. */
void Expr::bindVars(const StaticEnv & env)
{
abort();
}
void ExprInt::bindVars(const StaticEnv & env)
{
}
void ExprString::bindVars(const StaticEnv & env)
{
}
void ExprPath::bindVars(const StaticEnv & env)
{
}
void VarRef::bind(const StaticEnv & env)
{
/* Check whether the variable appears in the environment. If so,
set its level and displacement. */
const StaticEnv * curEnv;
unsigned int level;
int withLevel = -1;
for (curEnv = &env, level = 0; curEnv; curEnv = curEnv->up, level++) {
if (curEnv->isWith) {
if (withLevel == -1) withLevel = level;
} else {
StaticEnv::Vars::const_iterator i = curEnv->vars.find(name);
if (i != curEnv->vars.end()) {
fromWith = false;
this->level = level;
displ = i->second;
return;
}
}
}
/* Otherwise, the variable must be obtained from the nearest
enclosing `with'. If there is no `with', then we can issue an
"undefined variable" error now. */
if (withLevel == -1) throw EvalError(format("undefined variable `%1%'") % name);
fromWith = true;
this->level = withLevel;
}
void ExprVar::bindVars(const StaticEnv & env)
{
info.bind(env);
}
void ExprSelect::bindVars(const StaticEnv & env)
{
e->bindVars(env);
if (def) def->bindVars(env);
}
void ExprOpHasAttr::bindVars(const StaticEnv & env)
{
e->bindVars(env);
}
void ExprAttrs::bindVars(const StaticEnv & env)
{
if (recursive) {
StaticEnv newEnv(false, &env);
unsigned int displ = 0;
foreach (AttrDefs::iterator, i, attrs)
newEnv.vars[i->first] = i->second.displ = displ++;
foreach (AttrDefs::iterator, i, attrs)
if (i->second.inherited) i->second.var.bind(env);
else i->second.e->bindVars(newEnv);
}
else
foreach (AttrDefs::iterator, i, attrs)
if (i->second.inherited) i->second.var.bind(env);
else i->second.e->bindVars(env);
}
void ExprList::bindVars(const StaticEnv & env)
{
foreach (vector<Expr *>::iterator, i, elems)
(*i)->bindVars(env);
}
void ExprLambda::bindVars(const StaticEnv & env)
{
StaticEnv newEnv(false, &env);
unsigned int displ = 0;
if (!arg.empty()) newEnv.vars[arg] = displ++;
if (matchAttrs) {
foreach (Formals::Formals_::iterator, i, formals->formals)
newEnv.vars[i->name] = displ++;
foreach (Formals::Formals_::iterator, i, formals->formals)
if (i->def) i->def->bindVars(newEnv);
}
body->bindVars(newEnv);
}
void ExprLet::bindVars(const StaticEnv & env)
{
StaticEnv newEnv(false, &env);
unsigned int displ = 0;
foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
newEnv.vars[i->first] = i->second.displ = displ++;
foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
if (i->second.inherited) i->second.var.bind(env);
else i->second.e->bindVars(newEnv);
body->bindVars(newEnv);
}
void ExprWith::bindVars(const StaticEnv & env)
{
/* Does this `with' have an enclosing `with'? If so, record its
level so that `lookupVar' can look up variables in the previous
`with' if this one doesn't contain the desired attribute. */
const StaticEnv * curEnv;
unsigned int level;
prevWith = 0;
for (curEnv = &env, level = 1; curEnv; curEnv = curEnv->up, level++)
if (curEnv->isWith) {
prevWith = level;
break;
}
attrs->bindVars(env);
StaticEnv newEnv(true, &env);
body->bindVars(newEnv);
}
void ExprIf::bindVars(const StaticEnv & env)
{
cond->bindVars(env);
then->bindVars(env);
else_->bindVars(env);
}
void ExprAssert::bindVars(const StaticEnv & env)
{
cond->bindVars(env);
body->bindVars(env);
}
void ExprOpNot::bindVars(const StaticEnv & env)
{
e->bindVars(env);
}
void ExprConcatStrings::bindVars(const StaticEnv & env)
{
foreach (vector<Expr *>::iterator, i, *es)
(*i)->bindVars(env);
}
}