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#ifndef __EVAL_H
#define __EVAL_H
extern "C" {
#include <aterm2.h>
}
#include "hash.hh"
using namespace std;
/* Abstract syntax of Nix expressions.
An expression describes a (partial) state of the file system in a
referentially transparent way. The operational effect of
evaluating an expression is that the state described by the
expression is realised.
File : String * Content * [Expr] -> Expr
File(path, content, refs) specifies a file object (its full path
and contents), along with all file objects referenced by it (that
is, that it has pointers to). We assume that all files are
self-referential. This prevents us from having to deal with
cycles.
Derive : String * Expr * [Expr] * [String] -> Expr
Derive(platform, builder, ins, outs) specifies the creation of new
file objects (in paths declared by `outs') by the execution of a
program `builder' on a platform `platform'. This execution takes
place in a file system state and in an environment given by `ins'.
Str : String -> Expr
A string constant.
Tup : Expr * Expr -> Expr
Tuples of expressions.
Regular : String -> Content
Directory : [(String, Content)] -> Content
Hash : String -> Content
File content, given either explicitly or implicitly through a cryptographic hash.
The set of expressions in {\em $f$-normal form} is as follows:
File : String * Content * [FExpr] -> FExpr
These are completely evaluated Nix expressions.
The set of expressions in {\em $d$-normal form} is as follows:
File : String * Content * [DExpr] -> DExpr
Derive : String * DExpr * [Tup] * [String] -> DExpr
Tup : Str * DExpr -> Tup
Tup : Str * Str -> Tup
Str : String -> Str
These are Nix expressions in which the file system result of Derive
expressions has not yet been computed. This is useful for, e.g.,
querying dependencies.
*/
typedef ATerm Expr;
/* Evaluate an expression. */
Expr evalValue(Expr e);
/* Return a canonical textual representation of an expression. */
string printExpr(Expr e);
/* Perform variable substitution. */
Expr substExpr(string x, Expr rep, Expr e);
/* Hash an expression. */
Hash hashExpr(Expr e);
#endif /* !__EVAL_H */
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