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* Use a linked list of substitutions. This reduces the amount of

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copying.
This commit is contained in:
Eelco Dolstra 2006-05-02 21:39:02 +00:00
parent c791e94aee
commit 68174bdc7d
4 changed files with 54 additions and 19 deletions
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27
src/libexpr/nixexpr.hh
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@ -60,6 +60,31 @@ private:
typedef vector<ATerm> ATermVector;
/* A substitution is a linked list of ATermMaps that map names to
identifiers. We use a list of ATermMaps rather than a single to
make it easy to grow or shrink a substitution when entering a
scope. */
struct Substitution
{
ATermMap * map;
const Substitution * prev;
Substitution(const Substitution * prev, ATermMap * map)
{
this->prev = prev;
this->map = map;
}
Expr lookup(Expr name) const
{
Expr x;
for (const Substitution * s(this); s; s = s->prev)
if (x = s->map->get(name)) return x;
return 0;
}
};
/* Show a position. */
string showPos(ATerm pos);
@ -85,7 +110,7 @@ Expr queryAttr(Expr e, const string & name, ATerm & pos);
Expr makeAttrs(const ATermMap & attrs);
/* Perform a set of substitutions on an expression. */
Expr substitute(const ATermMap & subs, Expr e);
Expr substitute(const Substitution & subs, Expr e);
/* Check whether all variables are defined in the given expression.
Throw an exception if this isn't the case. */