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* Allow a default value in attribute selection by writing

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x.y.z or default

  (as originally proposed in
  https://mail.cs.uu.nl/pipermail/nix-dev/2009-September/002989.html).

  For instance, an expression like

    stdenv.lib.attrByPath ["features" "ckSched"] false args

  can now be written as

    args.features.ckSched or false
This commit is contained in:
Eelco Dolstra 2011-07-13 12:19:57 +00:00
parent 2b9e29b1c8
commit 0a623a10c7
9 changed files with 70 additions and 22 deletions
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36
src/libexpr/parser.y
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@ -237,7 +237,7 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
char * id; // !!! -> Symbol
char * path;
char * uri;
std::vector<nix::Symbol> * ids;
std::vector<nix::Symbol> * attrNames;
std::vector<nix::Expr *> * string_parts;
}
@ -247,14 +247,15 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
%type <attrs> binds
%type <formals> formals
%type <formal> formal
%type <ids> ids attrpath
%type <attrNames> attrs attrpath
%type <string_parts> string_parts ind_string_parts
%type <id> attr
%token <id> ID ATTRPATH
%token <e> STR IND_STR
%token <n> INT
%token <path> PATH
%token <uri> URI
%token IF THEN ELSE ASSERT WITH LET IN REC INHERIT EQ NEQ AND OR IMPL
%token IF THEN ELSE ASSERT WITH LET IN REC INHERIT EQ NEQ AND OR IMPL OR_KW
%token DOLLAR_CURLY /* == ${ */
%token IND_STRING_OPEN IND_STRING_CLOSE
%token ELLIPSIS
@ -326,7 +327,13 @@ expr_app
expr_select
: expr_simple '.' attrpath
{ $$ = new ExprSelect($1, *$3); }
{ $$ = new ExprSelect($1, *$3, 0); }
| expr_simple '.' attrpath OR_KW expr_select
{ $$ = new ExprSelect($1, *$3, $5); }
| /* Backwards compatibility: because Nixpkgs has a rarely used
function named ‘or’, allow stuff like ‘map or [...]’. */
expr_simple OR_KW
{ $$ = new ExprApp($1, new ExprVar(data->symbols.create("or"))); }
| expr_simple { $$ = $1; }
;
@ -370,7 +377,7 @@ ind_string_parts
binds
: binds attrpath '=' expr ';' { $$ = $1; addAttr($$, *$2, $4, makeCurPos(@2, data)); }
| binds INHERIT ids ';'
| binds INHERIT attrs ';'
{ $$ = $1;
foreach (AttrPath::iterator, i, *$3) {
if ($$->attrs.find(*i) != $$->attrs.end())
@ -379,26 +386,31 @@ binds
$$->attrs[*i] = ExprAttrs::AttrDef(*i, pos);
}
}
| binds INHERIT '(' expr ')' ids ';'
| binds INHERIT '(' expr ')' attrs ';'
{ $$ = $1;
/* !!! Should ensure sharing of the expression in $4. */
foreach (vector<Symbol>::iterator, i, *$6) {
if ($$->attrs.find(*i) != $$->attrs.end())
dupAttr(*i, makeCurPos(@6, data), $$->attrs[*i].pos);
$$->attrs[*i] = ExprAttrs::AttrDef(new ExprSelect($4, *i), makeCurPos(@6, data));
}}
}
}
| { $$ = new ExprAttrs; }
;
ids
: ids ID { $$ = $1; $1->push_back(data->symbols.create($2)); /* !!! dangerous */ }
attrs
: attrs attr { $$ = $1; $1->push_back(data->symbols.create($2)); /* !!! dangerous */ }
| { $$ = new vector<Symbol>; }
;
attrpath
: attrpath '.' ID { $$ = $1; $1->push_back(data->symbols.create($3)); }
| ID { $$ = new vector<Symbol>; $$->push_back(data->symbols.create($1)); }
: attrpath '.' attr { $$ = $1; $1->push_back(data->symbols.create($3)); }
| attr { $$ = new vector<Symbol>; $$->push_back(data->symbols.create($1)); }
;
attr
: ID { $$ = $1; }
| OR_KW { $$ = "or"; }
;
expr_list