forked from lix-project/lix
87 lines
1.9 KiB
C++
87 lines
1.9 KiB
C++
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#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 values:
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e := Hash(h) -- reference to expression value
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| External(h) -- reference to non-expression value
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| Str(s) -- string constant
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| Bool(b) -- boolean constant
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| App(e, e) -- application
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| Lam(x, e) -- lambda abstraction
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| Exec(platform, e, [(s, e)])
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-- primitive; execute e with args e* on platform
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;
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Semantics
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Each rules given as eval(e) => (e', h'), i.e., expression e has a
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normal form e' with hash code h'. evalE = fst . eval. evalH = snd
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. eval.
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eval(Hash(h)) => eval(loadExpr(h))
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eval(External(h)) => (External(h), h)
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eval(Str(s)@e) => (e, 0) # idem for Bool
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eval(App(e1, e2)) => eval(App(e1', e2))
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where e1' = evalE(e1)
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eval(App(Lam(var, body), arg)@in) =>
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eval(subst(var, arg, body))@out
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[AND write out to storage, and dbNFs[hash(in)] = hash(out) ???]
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eval(Exec(platform, prog, args)@e) =>
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(External(h), h)
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where
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hIn = hashExpr(e)
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fn = ... form name involving hIn ...
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h =
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if exec(evalE(platform) => Str(...)
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, getFile(evalH(prog))
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, map(makeArg . eval, args)
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) then
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hashExternal(fn)
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else
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undef
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makeArg((argn, (External(h), h))) => (argn, getFile(h))
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makeArg((argn, (Str(s), _))) => (argn, s)
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makeArg((argn, (Bool(True), _))) => (argn, "1")
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makeArg((argn, (Bool(False), _))) => (argn, undef)
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getFile :: Hash -> FileName
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loadExpr :: Hash -> FileName
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hashExpr :: Expr -> Hash
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hashExternal :: FileName -> Hash
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exec :: Platform -> FileName -> [(String, String)] -> Status
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*/
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typedef ATerm Expr;
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struct EvalResult
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{
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Expr e;
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Hash h;
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};
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/* Evaluate an expression. */
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EvalResult evalValue(Expr e);
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#endif /* !__EVAL_H */
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