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