This file describes the Pop-11 uses construct for loading library files.
Select headings to return to index
In Pop-11, the normal way to load libraries that are not autoloadable is with the syntax construct uses, which looks for library files in the directories given by * popuseslist.
uses works on the assumption that a library file 'foo.p' will define a corresponding identifier foo. If foo is already defined, uses takes this to mean the library is already loaded. Thus
uses foo;
may occur in multiple program files, but only the first occurrence will actually load the library.
The basic syntax of uses is just a comma-separated list of library names terminated by a semicolon, e.g.
uses foo, baz, ... ;
where the names refer to library files foo.p, baz.p, ... defining (at least) identifiers foo, baz, ... etc.
(Note that from within Ved, the command <ENTER> uses libname may be used for a single library.)
For normal interactive compilation, nothing further than the above is usually required. However, uses has two variants, uses-by_name and uses-now, plus additional syntax; these are described below.
The general syntax of uses is
uses - uses-by_name | lib-spec1, lib-spec2, ... ; uses-now -
where each lib-spec consists of a library name, optionally preceded by the keyword from, and optionally followed by a comma-separated list of other identifier names enclosed in parentheses:
[ from ] lib-name [ ( ident-name1, ident-name2, ... ) ]
lib-name is both the name of a library file and an identifier defined by that file: it may be a simple name, or a section pathname for a non top-level identifier, e.g.
uses foo, $-sect$-baz;
A identifier pathname such as $-sect$-baz is assumed to correspond to a filename
S-sectS-baz.p
that is, the corresponding filename is got by replacing `$` characters in the identifier pathname with `S`. (Note that you must specify the full identifier pathname starting with $-, since the current section is not taken into account.)
When other identifier names are present following lib-name, they refer to other identifiers defined by the same file. (Again, non top-level identifiers must be specified by full section pathnames.) These other identifiers (and the optional from keyword) are mainly relevant to uses-by_name.
Sometimes, a Pop-11 program file may use an identifier 'by name' only, that is, refer to it only via a quoted word (or quoted word-identifier). This usually involves * valof applied to the word, or using a Poplog VM code-planting procedure such as * sysCALL on the name of a procedure.
In these cases, uses-by_name may be employed instead of an ordinary uses:
uses-by_name foo, baz, ... ;
The effect of this is to delay the loading of each library file until such time as the corresponding identifier is actually fetched from its name (by a call to valof etc). In effect, uses-by_name makes the corresponding identifier autoloadable (regardless of whether the file defining it is in one of the normal autoloadable directories given by * popautolist).
Where a library file defines other identifiers in addition to the main (i.e. library name) one, you can also specify these as being used-by- name in a list following the main name, e.g.
uses-by_name foo (mary, joe, fred);
As with foo itself, the identifiers mary, joe, and fred then become autoloadable (any of them will load foo.p). Alternatively,
uses-by_name from foo (mary, joe, fred);
specifies that only the other identifiers are used by name, not the library name itself. Thus mary, joe, and fred become autoloadable, but not foo.
Unless you specifically want delayed loading, uses-by_name has no particularly advantage over uses for ordinary compilation; however, its use is more important for files that need to be compiled with Popc (see below).
(N.B. uses-by_name operates by assigning to the * sys_autoload_action of the words declared.)
Some library files define code for use at compile-time, such as
When a Pop-11 program file uses such a library (and the library is not autoloadable) the program file should specify uses-now for the library rather than uses. For example,
uses-now popxlib;
This reflects the fact the code from the library must actually be executed at compile-time, i.e. before or during compilation of the program file.
However, this distinction is irrelevant for normal interactive compilation, and only matters if the Popc compiler is to be used on the program file.
This section describes the way in which the Pop-11 object-module compiler Popc interprets the different variants of uses. See REF * POPC for more information.
In Popc compile mode, an ordinary uses statement
uses foo, baz, ... ;
does not actually cause any files to be loaded; rather, it merely records that the identifiers foo, baz, ... have been 'used'. At link time, this will force the extraction of the library modules defining the identifiers (even if they have not actually been referred to anywhere in the program being linked).
Thus the Popc behaviour of an ordinary uses is not appropriate when the libraries referred to define syntax words, macros, or other code which must actually be executed at compile-time. In this case, uses-now must be employed:
uses-now foo, baz, ... ;
This is effectively the same as surrounding an ordinary uses with normal_compile ... end_normal_compile, i.e. Popc compile mode is temporarily turned off, and the files are compiled as normal. (In normal compilation, uses-now is therefore the same as uses.)
In Popc, uses-by_name behaves like uses in that it forces identifiers to be extracted at link-time, but additionally ensures they are present in the run-time dictionary (so procedures like valof will work correctly when applied to the identifier name).
To inform Popc that identifiers are being 'used' regardless of which files define them, uses and uses-by_name may also be given identifier names directly, enclosed in parentheses:
uses (ident-name1, ident-name2, ...);
This usage is ignored in ordinary compilation.
HELP * LIBRARIES
REF * LIBRARY
Summary of library facilities in Poplog.
HELP * LOAD
Loading a file.
HELP * ECHOLOAD
'Echoes' a file on the terminal while loading it.
HELP * AUTOLOAD
The automatic compilation of files.
HELP * INITIAL
Initialising the Poplog system.
REF * POPC
The Pop-11 object module compiler
--- C.all/help/uses --- Copyright University of Sussex 1995. All rights reserved.