about summary refs log tree commit diff
path: root/src/libexpr/eval.cc
blob: cef346002962b4c40f6d8582497ecebbecfa6a96 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
#include "eval.hh"
#include "parser.hh"
#include "nixexpr-ast.hh"


EvalState::EvalState()
    : normalForms(32768, 50)
{
    blackHole = makeBlackHole();
    
    nrEvaluated = nrCached = 0;

    initNixExprHelpers();

    addPrimOps();
}


void EvalState::addPrimOp(const string & name,
    unsigned int arity, PrimOp primOp)
{
    primOps.set(name, makePrimOpDef(arity, ATmakeBlob(0, (void *) primOp)));
}


/* Substitute an argument set into the body of a function. */
static Expr substArgs(Expr body, ATermList formals, Expr arg)
{
    ATermMap subs;
    Expr undefined = makeUndefined();

    /* Get the formal arguments. */
    for (ATermIterator i(formals); i; ++i) {
        Expr name, def;
        if (matchNoDefFormal(*i, name))
            subs.set(name, undefined);
        else if (matchDefFormal(*i, name, def))
            subs.set(name, def);
        else abort(); /* can't happen */
    }

    /* Get the actual arguments, and check that they match with the
       formals. */
    ATermMap args;
    queryAllAttrs(arg, args);
    for (ATermIterator i(args.keys()); i; ++i) {
        Expr key = *i;
        Expr cur = subs.get(key);
        if (!cur)
            throw Error(format("unexpected function argument `%1%'")
                % aterm2String(key));
        subs.set(key, args.get(key));
    }

    /* Check that all arguments are defined. */
    for (ATermIterator i(subs.keys()); i; ++i)
        if (subs.get(*i) == undefined)
            throw Error(format("required function argument `%1%' missing")
                % aterm2String(*i));
    
    return substitute(subs, body);
}


/* Transform a mutually recursive set into a non-recursive set.  Each
   attribute is transformed into an expression that has all references
   to attributes substituted with selection expressions on the
   original set.  E.g., e = `rec {x = f x y; y = x;}' becomes `{x = f
   (e.x) (e.y); y = e.x;}'. */
ATerm expandRec(ATerm e, ATermList rbnds, ATermList nrbnds)
{
    ATerm name;
    Expr e2;
    Pos pos;

    /* Create the substitution list. */
    ATermMap subs;
    for (ATermIterator i(rbnds); i; ++i) {
        if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
        subs.set(name, makeSelect(e, name));
    }
    for (ATermIterator i(nrbnds); i; ++i) {
        if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
        subs.set(name, e2);
    }

    /* Create the non-recursive set. */
    ATermMap as;
    for (ATermIterator i(rbnds); i; ++i) {
        if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
        as.set(name, makeAttrRHS(substitute(subs, e2), pos));
    }

    /* Copy the non-recursive bindings.  !!! inefficient */
    for (ATermIterator i(nrbnds); i; ++i) {
        if (!matchBind(*i, name, e2, pos)) abort(); /* can't happen */
        as.set(name, makeAttrRHS(e2, pos));
    }

    return makeAttrs(as);
}


static Expr updateAttrs(Expr e1, Expr e2)
{
    /* Note: e1 and e2 should be in normal form. */

    ATermMap attrs;
    queryAllAttrs(e1, attrs, true);
    queryAllAttrs(e2, attrs, true);

    return makeAttrs(attrs);
}


string evalString(EvalState & state, Expr e)
{
    e = evalExpr(state, e);
    ATerm s;
    if (!matchStr(e, s)) throw Error("string expected");
    return aterm2String(s);
}


Path evalPath(EvalState & state, Expr e)
{
    e = evalExpr(state, e);
    ATerm s;
    if (!matchPath(e, s)) throw Error("path expected");
    return aterm2String(s);
}


bool evalBool(EvalState & state, Expr e)
{
    e = evalExpr(state, e);
    if (e == eTrue) return true;
    else if (e == eFalse) return false;
    else throw Error("boolean expected");
}


Expr evalExpr2(EvalState & state, Expr e)
{
    Expr e1, e2, e3, e4;
    ATerm name, pos;
    AFun sym = ATgetAFun(e);

    /* Normal forms. */
    if (sym == symStr ||
        sym == symPath ||
        sym == symSubPath ||
        sym == symUri ||
        sym == symNull ||
        sym == symInt ||
        sym == symBool ||
        sym == symFunction ||
        sym == symFunction1 ||
        sym == symAttrs ||
        sym == symList ||
        sym == symPrimOp)
        return e;
    
    /* The `Closed' constructor is just a way to prevent substitutions
       into expressions not containing free variables. */
    if (matchClosed(e, e1))
        return evalExpr(state, e1);

    /* Any encountered variables must be primops (since undefined
       variables are detected after parsing). */
    if (matchVar(e, name)) {
        ATerm primOp = state.primOps.get(name);
        if (!primOp)
            throw Error(format("impossible: undefined variable `%1%'") % name);
        int arity;
        ATermBlob fun;
        if (!matchPrimOpDef(primOp, arity, fun)) abort();
        if (arity == 0)
            return ((PrimOp) ATgetBlobData(fun)) (state, ATermVector());
        else
            return makePrimOp(arity, fun, ATempty);
    }

    /* Function application. */
    if (matchCall(e, e1, e2)) {

        ATermList formals;
        ATerm pos;
        
        /* Evaluate the left-hand side. */
        e1 = evalExpr(state, e1);

        /* Is it a primop or a function? */
        int arity;
        ATermBlob fun;
        ATermList args;
        if (matchPrimOp(e1, arity, fun, args)) {
            args = ATinsert(args, e2);
            if (ATgetLength(args) == arity) {
                /* Put the arguments in a vector in reverse (i.e.,
                   actual) order. */
                ATermVector args2(arity);
                for (ATermIterator i(args); i; ++i)
                    args2[--arity] = *i;
                return ((PrimOp) ATgetBlobData((ATermBlob) fun))
                    (state, args2);
            } else
                /* Need more arguments, so propagate the primop. */
                return makePrimOp(arity, fun, args);
        }

        else if (matchFunction(e1, formals, e4, pos)) {
            e2 = evalExpr(state, e2);
            try {
                return evalExpr(state, substArgs(e4, formals, e2));
            } catch (Error & e) {
                throw Error(format("while evaluating the function at %1%:\n%2%")
                    % showPos(pos) % e.msg());
            }
        }
        
        else if (matchFunction1(e1, name, e4, pos)) {
            try {
                ATermMap subs;
                subs.set(name, e2);
                return evalExpr(state, substitute(subs, e4));
            } catch (Error & e) {
                throw Error(format("while evaluating the function at %1%:\n%2%")
                    % showPos(pos) % e.msg());
            }
        }
        
        else throw Error("function or primop expected in function call");
    }

    /* Attribute selection. */
    if (matchSelect(e, e1, name)) {
        ATerm pos;
        string s1 = aterm2String(name);
        Expr a = queryAttr(evalExpr(state, e1), s1, pos);
        if (!a) throw Error(format("attribute `%1%' missing") % s1);
        try {
            return evalExpr(state, a);
        } catch (Error & e) {
            throw Error(format("while evaluating the attribute `%1%' at %2%:\n%3%")
                % s1 % showPos(pos) % e.msg());
        }
    }

    /* Mutually recursive sets. */
    ATermList rbnds, nrbnds;
    if (matchRec(e, rbnds, nrbnds))
        return expandRec(e, rbnds, nrbnds);

    /* Conditionals. */
    if (matchIf(e, e1, e2, e3)) {
        if (evalBool(state, e1))
            return evalExpr(state, e2);
        else
            return evalExpr(state, e3);
    }

    /* Assertions. */
    if (matchAssert(e, e1, e2, pos)) {
        if (!evalBool(state, e1))
            throw Error(format("assertion failed at %1%") % showPos(pos));
        return evalExpr(state, e2);
    }

    /* Withs. */
    if (matchWith(e, e1, e2, pos)) {
        ATermMap attrs;
        try {
            e1 = evalExpr(state, e1);
            queryAllAttrs(e1, attrs);
        } catch (Error & e) {
            throw Error(format("while evaluating the `with' definitions at %1%:\n%2%")
                % showPos(pos) % e.msg());
        }
        try {
            e2 = substitute(attrs, e2);
            checkVarDefs(state.primOps, e2);
            return evalExpr(state, e2);
        } catch (Error & e) {
            throw Error(format("while evaluating the `with' body at %1%:\n%2%")
                % showPos(pos) % e.msg());
        } 
    }

    /* Generic equality. */
    if (matchOpEq(e, e1, e2))
        return makeBool(evalExpr(state, e1) == evalExpr(state, e2));

    /* Generic inequality. */
    if (matchOpNEq(e, e1, e2))
        return makeBool(evalExpr(state, e1) != evalExpr(state, e2));

    /* Negation. */
    if (matchOpNot(e, e1))
        return makeBool(!evalBool(state, e1));

    /* Implication. */
    if (matchOpImpl(e, e1, e2))
        return makeBool(!evalBool(state, e1) || evalBool(state, e2));

    /* Conjunction (logical AND). */
    if (matchOpAnd(e, e1, e2))
        return makeBool(evalBool(state, e1) && evalBool(state, e2));

    /* Disjunction (logical OR). */
    if (matchOpOr(e, e1, e2))
        return makeBool(evalBool(state, e1) || evalBool(state, e2));

    /* Attribute set update (//). */
    if (matchOpUpdate(e, e1, e2))
        return updateAttrs(evalExpr(state, e1), evalExpr(state, e2));

    /* Attribute existence test (?). */
    if (matchOpHasAttr(e, e1, name)) {
        ATermMap attrs;
        queryAllAttrs(evalExpr(state, e1), attrs);
        return makeBool(attrs.get(name) != 0);
    }

    /* String or path concatenation. */
    if (matchOpPlus(e, e1, e2)) {
        e1 = evalExpr(state, e1);
        e2 = evalExpr(state, e2);
        ATerm s1, s2;
        if (matchStr(e1, s1) && matchStr(e2, s2))
            return makeStr(string2ATerm((
                (string) aterm2String(s1) + (string) aterm2String(s2)).c_str()));
        else if (matchPath(e1, s1) && matchPath(e2, s2))
            return makePath(string2ATerm(canonPath(
                (string) aterm2String(s1) + "/" + (string) aterm2String(s2)).c_str()));
        else throw Error("wrong argument types in `+' operator");
    }

    /* Barf. */
    throw badTerm("invalid expression", e);
}


Expr evalExpr(EvalState & state, Expr e)
{
    checkInterrupt();
    
    startNest(nest, lvlVomit,
        format("evaluating expression: %1%") % e);

    state.nrEvaluated++;

    /* Consult the memo table to quickly get the normal form of
       previously evaluated expressions. */
    Expr nf = state.normalForms.get(e);
    if (nf) {
        if (nf == state.blackHole)
            throw Error("infinite recursion encountered");
        state.nrCached++;
        return nf;
    }

    /* Otherwise, evaluate and memoize. */
    state.normalForms.set(e, state.blackHole);
    nf = evalExpr2(state, e);
    state.normalForms.set(e, nf);
    return nf;
}


Expr evalFile(EvalState & state, const Path & path)
{
    startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path);
    Expr e = parseExprFromFile(state, path);
    try {
        return evalExpr(state, e);
    } catch (Error & e) {
        throw Error(format("while evaluating the file `%1%':\n%2%")
            % path % e.msg());
    }
}


void printEvalStats(EvalState & state)
{
    debug(format("evaluated %1% expressions, %2% cache hits, %3%%% efficiency")
        % state.nrEvaluated % state.nrCached
        % ((float) state.nrCached / (float) state.nrEvaluated * 100));
}