lix/src/libexpr/eval.hh
Eelco Dolstra 85d13c8f93 * Change the semantics of "with" so that inner "withs" take
precedence, i.e. `with {x=1;}; with {x=2;}; x' evaluates to 2'.
  This has a simpler implementation and seems more natural.  There
  doesn't seem to be any code in Nixpkgs or NixOS that relies on the
  old behaviour.
2010-04-14 08:37:08 +00:00

293 lines
7 KiB
C++

#ifndef __EVAL_H
#define __EVAL_H
#include <map>
#include "nixexpr.hh"
#include "symbol-table.hh"
namespace nix {
class Hash;
class EvalState;
struct Env;
struct Value;
typedef std::map<Symbol, Value> Bindings;
struct Env
{
Env * up;
Bindings bindings;
};
typedef enum {
tInt = 1,
tBool,
tString,
tPath,
tNull,
tAttrs,
tList,
tThunk,
tApp,
tLambda,
tCopy,
tBlackhole,
tPrimOp,
tPrimOpApp,
} ValueType;
typedef void (* PrimOp) (EvalState & state, Value * * args, Value & v);
struct Value
{
ValueType type;
union
{
int integer;
bool boolean;
/* Strings in the evaluator carry a so-called `context' (the
ATermList) which is a list of strings representing store
paths. This is to allow users to write things like
"--with-freetype2-library=" + freetype + "/lib"
where `freetype' is a derivation (or a source to be copied
to the store). If we just concatenated the strings without
keeping track of the referenced store paths, then if the
string is used as a derivation attribute, the derivation
will not have the correct dependencies in its inputDrvs and
inputSrcs.
The semantics of the context is as follows: when a string
with context C is used as a derivation attribute, then the
derivations in C will be added to the inputDrvs of the
derivation, and the other store paths in C will be added to
the inputSrcs of the derivations.
For canonicity, the store paths should be in sorted order. */
struct {
const char * s;
const char * * context;
} string;
const char * path;
Bindings * attrs;
struct {
unsigned int length;
Value * elems;
} list;
struct {
Env * env;
Expr * expr;
} thunk;
struct {
Value * left, * right;
} app;
struct {
Env * env;
ExprLambda * fun;
} lambda;
Value * val;
struct {
PrimOp fun;
unsigned int arity;
} primOp;
struct {
Value * left, * right;
unsigned int argsLeft;
} primOpApp;
};
};
static inline void mkInt(Value & v, int n)
{
v.type = tInt;
v.integer = n;
}
static inline void mkBool(Value & v, bool b)
{
v.type = tBool;
v.boolean = b;
}
static inline void mkThunk(Value & v, Env & env, Expr * expr)
{
v.type = tThunk;
v.thunk.env = &env;
v.thunk.expr = expr;
}
static inline void mkCopy(Value & v, Value & src)
{
v.type = tCopy;
v.val = &src;
}
void mkString(Value & v, const char * s);
void mkString(Value & v, const string & s, const PathSet & context = PathSet());
void mkPath(Value & v, const char * s);
typedef std::map<Path, Hash> DrvHashes;
/* Cache for calls to addToStore(); maps source paths to the store
paths. */
typedef std::map<Path, Path> SrcToStore;
struct EvalState;
std::ostream & operator << (std::ostream & str, Value & v);
class EvalState
{
public:
DrvHashes drvHashes; /* normalised derivation hashes */
SymbolTable symbols;
const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName;
private:
SrcToStore srcToStore;
bool allowUnsafeEquality;
std::map<Path, Expr *> parseTrees;
public:
EvalState();
~EvalState();
/* Evaluate an expression read from the given file to normal
form. */
void evalFile(const Path & path, Value & v);
/* Evaluate an expression to normal form, storing the result in
value `v'. */
void eval(Expr * e, Value & v);
void eval(Env & env, Expr * e, Value & v);
/* Evaluation the expression, then verify that it has the expected
type. */
bool evalBool(Env & env, Expr * e);
/* If `v' is a thunk, enter it and overwrite `v' with the result
of the evaluation of the thunk. If `v' is a delayed function
application, call the function and overwrite `v' with the
result. Otherwise, this is a no-op. */
void forceValue(Value & v);
/* Force a value, then recursively force list elements and
attributes. */
void strictForceValue(Value & v);
/* Force `v', and then verify that it has the expected type. */
int forceInt(Value & v);
bool forceBool(Value & v);
void forceAttrs(Value & v);
void forceList(Value & v);
void forceFunction(Value & v); // either lambda or primop
string forceString(Value & v);
string forceString(Value & v, PathSet & context);
string forceStringNoCtx(Value & v);
/* Return true iff the value `v' denotes a derivation (i.e. a
set with attribute `type = "derivation"'). */
bool isDerivation(Value & v);
/* String coercion. Converts strings, paths and derivations to a
string. If `coerceMore' is set, also converts nulls, integers,
booleans and lists to a string. If `copyToStore' is set,
referenced paths are copied to the Nix store as a side effect.q */
string coerceToString(Value & v, PathSet & context,
bool coerceMore = false, bool copyToStore = true);
/* Path coercion. Converts strings, paths and derivations to a
path. The result is guaranteed to be a canonicalised, absolute
path. Nothing is copied to the store. */
Path coerceToPath(Value & v, PathSet & context);
private:
/* The base environment, containing the builtin functions and
values. */
Env & baseEnv;
void createBaseEnv();
void addConstant(const string & name, Value & v);
void addPrimOp(const string & name,
unsigned int arity, PrimOp primOp);
Value * lookupVar(Env * env, const Symbol & name);
friend class ExprVar;
friend class ExprAttrs;
friend class ExprLet;
public:
/* Do a deep equality test between two values. That is, list
elements and attributes are compared recursively. */
bool eqValues(Value & v1, Value & v2);
void callFunction(Value & fun, Value & arg, Value & v);
/* Automatically call a function for which each argument has a
default value or has a binding in the `args' map. */
void autoCallFunction(const Bindings & args, Value & fun, Value & res);
/* Allocation primitives. */
Value * allocValues(unsigned int count);
Env & allocEnv();
void mkList(Value & v, unsigned int length);
void mkAttrs(Value & v);
void mkThunk_(Value & v, Expr * expr);
void cloneAttrs(Value & src, Value & dst);
/* Print statistics. */
void printStats();
private:
unsigned long nrValues;
unsigned long nrEnvs;
unsigned long nrEvaluated;
unsigned int recursionDepth;
unsigned int maxRecursionDepth;
char * deepestStack; /* for measuring stack usage */
friend class RecursionCounter;
};
/* Return a string representing the type of the value `v'. */
string showType(Value & v);
}
#endif /* !__EVAL_H */