| Eval and code interpretation |
|---|
|
|
|
This chapter describes the Bigloo evaluator.
Bigloo includes an interpreter. Unfortunately, the language accepted by the
interpreter is a proper subset of that accepted by the compiler. The main
differences are: - No foreign objects can be handled by interpreter.
- Classes of the object system cannot be declared within interpreted
code.
- The interpreter ignores modules, and has a unique global environment.
Compiled code and interpreted code can be mixed together. That
is, interpreted code is allowed to call compiled code and vice
versa. This connection can be use to circumvent the missing
features of the interpreter (see Section see Module Declaration,
for a description of how to connect compiled and interpreted code). By default the evaluator assumes that operators from the standard
library (e.g., +, car) are immutable. Hence, it optimizes
these operators's calls. This optimization can be disabled using
the bigloo-eval-strict-module parameter described in
the chapter describing the parameters (see see Parameters).
23.2 Eval standard functions
|
This form evaluates exp. The second argument is optional. It can be
the evaluation of one of these three function forms:
(scheme-report-environment 5)
(null-environment 5)
(interaction-environment)
|
|
| scheme-report-environment version | procedure |
null-environment version | procedure |
interaction-environment version | procedure |
These three procedures have the definitions given in the R5RS so see
info-file `r5rs.info', 6.5 Eval, for more
details.
|
| byte-code-compile exp [env (default-environment)] | bigloo procedure |
| byte-code-run byte-code | bigloo procedure |
The function byte-code-compile compiles a Scheme expression into
a sequence of byte codes that is implemented as a string.
The function byte-code-run execute such a sequence.
|
This invokes the read-eval-print loop. Several repl
can be embedded.
The repl function can be used to implement custom Bigloo interpreters.
For instance, one may write:
When compiled, this will deliver an executable containingthe sole Bigloo interpreter.
|
| set-repl-error-notifier! notifier | bigloo procedure |
| get-repl-error-notifier | bigloo procedure |
Set or get the procedure used in the REPLs to display errors. The notifier
is a procedure of one argument, the error or exception that has been
raised. Example:
(set-repl-error-notifier!
(lambda (e)
(print "=== error ======)
(exception-notify e)))
|
|
This exits from the currently running repl. If the current
repl is the first one then this function ends the interpreter.
|
| set-prompter! proc | bigloo procedure |
The argument proc has to be a procedure of one argument and invoking
this function sets the repl prompter. That is, to display its prompt,
repl invokes proc giving it the nesting level of the
current loop as its argument.
|
| get-prompter | bigloo procedure |
Returns the current repl prompter.
|
| set-repl-printer! proc | bigloo procedure |
The argument proc has to be a procedure accepting one or two arguments.
This function sets the repl display function. That is, to display the
result of its evaluations, repl invokes proc giving it the
evaluated expression as first argument and the current output port (or
a file in case of transcript) as second argument. Set-repl-printer!
returns the former repl display function.
For instance, one may write:
1:=> (define x (cons 1 2)) -| X
1:=> (define y (cons x x)) -| Y
1:=> y -| (#0=(1 . 2) . #0#)
1:=> (set-repl-printer! display) -| #<procedure:83b8c70.-2>
1:=> y -| ((1 . 2) 1 . 2)
|
|
| native-repl-printer | bigloo procedure |
Returns the native (default) repl display function.
|
| expand exp | bigloo procedure |
Returns the value of exp after all macro expansions
have been performed.
|
| expand-once exp | bigloo procedure |
Returns the value of exp after one macro expansion has been performed.
|
It is possible to specify files which have to be loaded when the interpreter
is invoked. For this, see section see Compiler Description. If a Bigloo file starts with the line:
and if this file is executable (in the meaning of the system) and if the user
tries to execute it, Bigloo will evaluate it. Note also that SRFI-22 support
enables to run any Unix interpreter (see SRFIs).
| load filename | bigloo procedure |
| loadq filename | bigloo procedure |
Filename should be a string naming an existing file which contains
Bigloo source code. This file is searched in the current directory and
in all the directories mentioned in the variable *load-path*.
The load procedure reads expressions and
definitions from the file, evaluating them sequentially. If the file
loaded is a module (i.e. if it begins with a regular
module clause), load behaves as module initialization. Otherwise, this
function returns the result of the last evaluation. The function loadq
differs from the function load in the sense that loadq does
not print any intermediate evaluations.
Both functions return the full path of the loaded file.
|
| loada filename | bigloo procedure |
Loads an ``access file'', which allows the interpreter to find
the modules imported by a loaded module. It returns the full path
of the loaded file.
|
| *load-path* | bigloo variable |
A list of search paths for the load functions.
|
| dynamic-load filename #!optional (init init-point) | bigloo procedure |
Loads a shared library named filename. Returns the value of the
last top-level expression.
Important note: The function dynamic-load can only be
used from compiled modules linked against dynamic libraries. In particular,
the dynamic-load function can be issued from the bigloo
command if and only if the option --sharedcompiler=yes has been
used when configuring Bigloo. If the bigloo command is not linked
against dynamic libraries and if dynamic-load is
required inside a read-eval-print loop (REPL) it exists a simple workaround.
It consists in implementing a new REPL and linking it against dynamic
libraries. This can be done as:
$ cat > new-repl.scm <<EOF
(module new-repl)
(repl)
EOF
$ bigloo new-repl.scm -o new-repl
$ new-repl
1:=> (dynamic-load ...)
|
If init-point is specified and if it is a string and if the
library defines a function named init-point, this function is
called when the library is loaded. Init-point is a C identifier,
not a Scheme identifier. In order to set the C name a Scheme function,
use the extern export clause (see Section see C Interface). If the init-point is provided and is not a string,
no initialization function is called after the library is loaded. If
the init-point value is not provided, once the library is
loaded, dynamic-load uses the Bigloo default entry
point. Normally you should not provide an init-point to
dynamic-load unless you known what you are doing. When
producing C code, to force the Bigloo compiler to emit such a default
entry point, use the -dload-sym compilation option (see Section
see Compiler Description). This option is useless when using the
JVM code generator. Let's assume a Linux system and two Bigloo
modules. The first:
(module mod1
(eval (export foo))
(export (foo x)))
(define (foo x)
(print "foo: " x))
(foo 4)
|
The second:
(module mod2
(import (mod1 "mod1.scm"))
(eval (export bar))
(export (bar x)))
(define (bar x)
(print "bar: " x))
(bar 5)
|
If these modules are compiled as:
$ bigloo mod1.scm -c -o mod1.o
$ bigloo mod2.scm -c -o mod2.o -dload-sym
|
Then, if a shared library is built using these two modules (note that on
non Linux systems, a different command line is required):
$ ld -G -o lib.so mod1.o mod2.o
|
Then, lib.so cant be dynamically loaded and the variables it defines
used such as :
$ bigloo -i
(dynamic-load "lib.so")
-| foo: 4
bar: 5
1:=> (foo 6)
-| foo: 7
|
As the example illustrates, when Bigloo modules are dynamically loaded,
they are initialized. This initialization is ensure only if
dynamic-load is called with exactly one parameter. If
dynamic-load is called with two parameters, it is of the
responsibility of the program to initialize the dynamically loaded
module before using any Scheme reference.
Note: In order to let the loaded module accesses the variables
defined by the loader application, special compilation flags must be
used (e.g., -rdynamic under the Linux operating
system). Dynamic-load is implemented on the top of the
dlopen facility. For more information read the dlopen and
ld manuals.
|
| dynamic-unload filename | bigloo procedure |
On the operating system that supports this facility, unloads a shared library.
Returns #t on success. Returns #f otherwise.
|
| *dynamic-load-path* | bigloo variable |
A list of search paths for the dynamic-load functions.
|
| dynamic-load-symbol filename name #!optional module | bigloo-procedure |
| dynamic-load-symbol-get dlsym | bigloo-procedure |
| dynamic-load-symbol-set dlsym val | bigloo-procedure |
The function dynamic-load-symbol looks up for a variable in the
dynamic library filename. If found, it returns a custom
Bigloo object denoting that variable. Otherwise it returns #f.
This function assumes that filename has previously been successfully
loaded with dynamic-load. If not, an error is raised. The argument
filename must be equal (in the sense of string=? to the argument
used to load the library.
The C name of the looked up variable is name is module is
not provided. Otherwise, it is the result of calling bigloo-module-mangle
with name and module as arguments.
The function dynamic-load-symbol-get returns the value of a
dynamically loaded variable.
The function dynamic-load-symbol-set sets the value of a dynamic
loaded variable. It assumes that the variable is writable, i.e., that it has
not been compiled as a C constant.
|
| transcript-on filename | procedure |
|
23.3 Eval command line options
|
This section presents the Bigloo compiler options that impact the interaction
between compiled and interpreted code. The whole list of the Bigloo
compiler options can be found in
The Bigloo command line. -i Don't compile a module, interpret it!
-export-all Make all the bindings defined by
the compiled module available from the interpreter.
-export-export Make all the bindings exported by the
compiled module available from the interpreter.
-export-mutable Make all the bindings exported by the
compiled module mutable from outside the module. This option is
dangerous! Either all the modules composing the application
must be compiled with or without -export-mutable. It is impossible
to mix -export-mutable enabled and disabled compilations.
23.4 Eval and the foreign interface
|
To be able to get access to foreign functions within the Bigloo
interpreter, some extra measurements have to be taken. The foreign
functions have to be present in the interpreter binary, which means you
have to compile a custom interpreter. This is described in
Section Using C bindings within the interpreter.
|