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
|
#include "eval.hh"
#include "expr.hh"
#include "parser.hh"
#include "primops.hh"
EvalState::EvalState()
{
blackHole = ATmake("BlackHole()");
if (!blackHole) throw Error("cannot build black hole");
nrEvaluated = nrCached = 0;
}
Expr getAttr(EvalState & state, Expr e, const string & name)
{
}
/* Substitute an argument set into the body of a function. */
static Expr substArgs(Expr body, ATermList formals, Expr arg)
{
Subs subs;
Expr undefined = ATmake("Undefined");
/* Get the formal arguments. */
while (!ATisEmpty(formals)) {
char * s;
if (!ATmatch(ATgetFirst(formals), "<str>", &s))
abort(); /* can't happen */
subs[s] = undefined;
formals = ATgetNext(formals);
}
/* Get the actual arguments, and check that they match with the
formals. */
Attrs args;
queryAllAttrs(arg, args);
for (Attrs::iterator i = args.begin(); i != args.end(); i++) {
if (subs.find(i->first) == subs.end())
throw badTerm(format("argument `%1%' not declared") % i->first, arg);
subs[i->first] = i->second;
}
/* Check that all arguments are defined. */
for (Subs::iterator i = subs.begin(); i != subs.end(); i++)
if (i->second == undefined)
throw badTerm(format("formal argument `%1%' missing") % i->first, arg);
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 bnds)
{
/* Create the substitution list. */
Subs subs;
ATermList bs = bnds;
while (!ATisEmpty(bs)) {
char * s;
Expr e2;
if (!ATmatch(ATgetFirst(bs), "Bind(<str>, <term>)", &s, &e2))
abort(); /* can't happen */
subs[s] = ATmake("Select(<term>, <str>)", e, s);
bs = ATgetNext(bs);
}
/* Create the non-recursive set. */
Attrs as;
bs = bnds;
while (!ATisEmpty(bs)) {
char * s;
Expr e2;
if (!ATmatch(ATgetFirst(bs), "Bind(<str>, <term>)", &s, &e2))
abort(); /* can't happen */
as[s] = substitute(subs, e2);
bs = ATgetNext(bs);
}
return makeAttrs(as);
}
string evalString(EvalState & state, Expr e)
{
e = evalExpr(state, e);
char * s;
if (!ATmatch(e, "Str(<str>)", &s))
throw badTerm("string expected", e);
return s;
}
Path evalPath(EvalState & state, Expr e)
{
e = evalExpr(state, e);
char * s;
if (!ATmatch(e, "Path(<str>)", &s))
throw badTerm("path expected", e);
return s;
}
bool evalBool(EvalState & state, Expr e)
{
e = evalExpr(state, e);
if (ATmatch(e, "True")) return true;
else if (ATmatch(e, "False")) return false;
else throw badTerm("expecting a boolean", e);
}
Expr evalExpr2(EvalState & state, Expr e)
{
Expr e1, e2, e3, e4;
char * s1;
/* Normal forms. */
if (ATmatch(e, "Str(<str>)", &s1) ||
ATmatch(e, "Path(<str>)", &s1) ||
ATmatch(e, "Uri(<str>)", &s1) ||
ATmatch(e, "Function([<list>], <term>)", &e1, &e2) ||
ATmatch(e, "Attrs([<list>])", &e1) ||
ATmatch(e, "List([<list>])", &e1))
return e;
/* Any encountered variables must be undeclared or primops. */
if (ATmatch(e, "Var(<str>)", &s1)) {
return e;
}
/* Function application. */
if (ATmatch(e, "Call(<term>, <term>)", &e1, &e2)) {
/* Evaluate the left-hand side. */
e1 = evalExpr(state, e1);
/* Is it a primop or a function? */
if (ATmatch(e1, "Var(<str>)", &s1)) {
string primop(s1);
if (primop == "import") return primImport(state, e2);
if (primop == "derivation") return primDerivation(state, e2);
else throw badTerm("undefined variable/primop", e1);
}
else if (ATmatch(e1, "Function([<list>], <term>)", &e3, &e4)) {
return evalExpr(state,
substArgs(e4, (ATermList) e3, evalExpr(state, e2)));
}
else throw badTerm("expecting a function or primop", e1);
}
/* Attribute selection. */
if (ATmatch(e, "Select(<term>, <str>)", &e1, &s1)) {
string name(s1);
Expr a = queryAttr(evalExpr(state, e1), name);
if (!a) throw badTerm(format("missing attribute `%1%'") % name, e);
return evalExpr(state, a);
}
/* Mutually recursive sets. */
ATermList bnds;
if (ATmatch(e, "Rec([<list>])", &bnds))
return expandRec(e, (ATermList) bnds);
/* Let expressions `let {..., body = ...}' are just desugared
into `(rec {..., body = ...}).body'. */
if (ATmatch(e, "LetRec(<term>)", &e1))
return evalExpr(state, ATmake("Select(Rec(<term>), \"body\")", e1));
/* Conditionals. */
if (ATmatch(e, "If(<term>, <term>, <term>)", &e1, &e2, &e3)) {
if (evalBool(state, e1))
return evalExpr(state, e2);
else
return evalExpr(state, e3);
}
/* Equality. Just strings for now. */
if (ATmatch(e, "OpEq(<term>, <term>)", &e1, &e2)) {
string s1 = evalString(state, e1);
string s2 = evalString(state, e2);
return s1 == s2 ? ATmake("True") : ATmake("False");
}
/* Barf. */
throw badTerm("invalid expression", e);
}
Expr evalExpr(EvalState & state, Expr e)
{
Nest nest(lvlVomit, format("evaluating expression: %1%") % printTerm(e));
state.nrEvaluated++;
/* Consult the memo table to quickly get the normal form of
previously evaluated expressions. */
NormalForms::iterator i = state.normalForms.find(e);
if (i != state.normalForms.end()) {
if (i->second == state.blackHole)
throw badTerm("infinite recursion", e);
state.nrCached++;
return i->second;
}
/* Otherwise, evaluate and memoize. */
state.normalForms[e] = state.blackHole;
Expr nf = evalExpr2(state, e);
state.normalForms[e] = nf;
return nf;
}
Expr evalFile(EvalState & state, const Path & path)
{
Nest nest(lvlTalkative, format("evaluating file `%1%'") % path);
Expr e = parseExprFromFile(path);
return evalExpr(state, e);
}
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));
}
|
