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* Added syntactic sugar to the construction of attribute sets to

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`inherit' variables from the surrounding lexical scope.

  E.g.,

    {stdenv, libfoo}: derivation {
      builder = ./bla;
      inherit stdenv libfoo;
      xyzzy = 1;
    }

  is equivalent to

    {stdenv, libfoo}: derivation {
      builder = ./bla;
      stdenv = stdenv;
      libfoo = libfoo;
      xyzzy = 1;
    }

  Note that for mutually recursive attribute set definitions (`rec
  {...}'), this also works, that is, `rec {inherit x;}' is equivalent
  to `let {fresh = x; body = rec {x = fresh;};}', *not*
  `rec {x = x}'.
This commit is contained in:
Eelco Dolstra 2004-02-02 21:39:33 +00:00
parent d9f30fe7c7
commit 1c9c0a5a46
6 changed files with 78 additions and 41 deletions
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30
src/libexpr/eval.cc
View file

@ -55,15 +55,15 @@ static Expr substArgs(Expr body, ATermList formals, Expr arg)
/* Transform a mutually recursive set into a non-recursive set. Each
attribute is transformed into an expression that has all references
to attributes substituted with selection expressions on the
original set. E.g., e = `rec {x = f x y, y = x}' becomes `{x = f
(e.x) (e.y), y = e.x}'. */
ATerm expandRec(ATerm e, ATermList bnds)
original set. E.g., e = `rec {x = f x y; y = x;}' becomes `{x = f
(e.x) (e.y); y = e.x;}'. */
ATerm expandRec(ATerm e, ATermList rbnds, ATermList nrbnds)
{
ATMatcher m;
/* Create the substitution list. */
ATermMap subs;
for (ATermIterator i(bnds); i; ++i) {
for (ATermIterator i(rbnds); i; ++i) {
string s;
Expr e2;
if (!(atMatch(m, *i) >> "Bind" >> s >> e2))
@ -73,7 +73,7 @@ ATerm expandRec(ATerm e, ATermList bnds)
/* Create the non-recursive set. */
ATermMap as;
for (ATermIterator i(bnds); i; ++i) {
for (ATermIterator i(rbnds); i; ++i) {
string s;
Expr e2;
if (!(atMatch(m, *i) >> "Bind" >> s >> e2))
@ -81,6 +81,15 @@ ATerm expandRec(ATerm e, ATermList bnds)
as.set(s, substitute(subs, e2));
}
/* Copy the non-recursive bindings. !!! inefficient */
for (ATermIterator i(nrbnds); i; ++i) {
string s;
Expr e2;
if (!(atMatch(m, *i) >> "Bind" >> s >> e2))
abort(); /* can't happen */
as.set(s, e2);
}
return makeAttrs(as);
}
@ -175,14 +184,9 @@ Expr evalExpr2(EvalState & state, Expr e)
}
/* Mutually recursive sets. */
ATermList bnds;
if (atMatch(m, e) >> "Rec" >> bnds)
return expandRec(e, bnds);
/* Let expressions `let {..., body = ...}' are just desugared
into `(rec {..., body = ...}).body'. */
if (atMatch(m, e) >> "LetRec" >> bnds)
return evalExpr(state, ATmake("Select(Rec(<term>), \"body\")", bnds));
ATermList rbnds, nrbnds;
if (atMatch(m, e) >> "Rec" >> rbnds >> nrbnds)
return expandRec(e, rbnds, nrbnds);
/* Conditionals. */
if (atMatch(m, e) >> "If" >> e1 >> e2 >> e3) {