Author: leo
Date: Wed Aug 3 03:34:54 2005
New Revision: 8772
Modified:
trunk/docs/compiler_faq.pod
Log:
Update compiler_faq.pod
* howto delete globals, lexicals
* howto access %ENV, %Config
* some more notes about tailcalls, source comments, classes, ...
Modified: trunk/docs/compiler_faq.pod
==============================================================================
--- trunk/docs/compiler_faq.pod (original)
+++ trunk/docs/compiler_faq.pod Wed Aug 3 03:34:54 2005
@@ -28,10 +28,13 @@ See C<languages/tcl/tcl.pir_template>'s
=head2 How do I embed source locations in my code for debugging?
-You can do this using the C<setfile> and C<setline> opcodes. Simply
-set the source file name or line number whenever it changes. This is
-sub-optimal for a number of reasons, so there should eventually be a
-better system for this.
+You can do this using either the C<setfile> and C<setline> opcodes or
+with C-like C<#line> comments:
+
+ #line 27 "my_source.file"
+
+Simply set the source file name or line number whenever it changes. But note
+that currently (Parrot 0.2.x) both are ignored in the lexer.
=head1 Subroutines
@@ -63,6 +66,19 @@ The method name may also be a string var
m = "bold"
curses_obj.m()
+=head2 How do I generate a tailcall in PIR?
+
+ .sub foo
+ # do something
+ .return bar(42) # tailcall sub bar
+ .end
+
+ .sub bar
+ # ...
+ .end
+
+The sub C<bar> will return to the caller of C<foo>.
+
=head2 How do I generate a sub call with a variable-length parameter list in
PIR?
Use unprototyped calls and functions and pass as many arguments as you have.
@@ -125,6 +141,27 @@ or the C<find_global> op:
find_global $P0, "name_of_the_global"
+=head2 How can I delete a global
+
+You can retrieve the namespace hash and use the C<delete> opcode.
+Nested namespace names have a NUL char prepended to their name.
+
+ .sub main @MAIN
+ $P0 = new Integer
+ store_global "foo", $P0
+ store_global "Bar", "baz", $P0
+ # ...
+ .include "interpinfo.pasm"
+ .local pmc ns, Bar_ns
+ ns = interpinfo .INTERPINFO_NAMESPACE_ROOT
+ delete ns["foo"] # delete from top level
+ Bar_ns = ns["\0Bar"] # get Bar namespace
+ delete Bar_ns["baz"]
+ $P0 = find_global "Bar", "baz"
+ print "never\n"
+ .end
+
+
=head2 How do I use lexical pads to have both a function scope and a global
scope?
To create lexical variables, you'll need to keep track of how deeply
@@ -197,7 +234,7 @@ instead of:
You will still need to do a C<store_lex> at some point (probably at the start
of the block in which it is declared) to create the variable in the first
-place. Put a ParrotReference in it or something.
+place. Put a C<Undef> PMC in it or something.
If, on the other hand, you never find said lexical variable (or if a
block declares that variable to be global, or whatever other tricks
@@ -207,6 +244,21 @@ can access much the same way:
find_global $P0, "bar"
assign $P0, value_to_store
+=head2 How can I delete a lexical
+
+You can C<peek_pad> the current pad and use C<delete>.
+
+ .sub main @MAIN
+ new_pad 0
+ $P0 = new Integer
+ store_lex -1, "foo", $P0
+ .local pmc pad
+ pad = peek_pad
+ delete pad["foo"] # delete from current pad
+ $P0 = find_lex "foo"
+ print "never\n"
+ .end
+
=head2 How do I resolve a variable name?
Use C<find_name>:
@@ -250,6 +302,13 @@ With the C<newclass> op:
newclass $P0, "Animal"
+=head2 How do I add instance variables/attributes?
+
+Each class knows what attribute its object can have. You can add
+attributes to a class (not to individual objects) like so:
+
+ addattribute $P0, "legs"
+
=head2 How do I add instance methods to a class?
Methods are declared as functions in the class namespace with the
@@ -257,24 +316,23 @@ C<method> keyword appended to the functi
.namespace [ "Animal" ]
- .sub initialise method
- setattribute self, ...
+ .sub __init method
+ $P0 = new Integer
+ setattribute self, "legs", $P0
...
.end
.sub run method
...
.end
-=head2 How do I add instance variables/attributes?
-
-Each class knows what attribute its object can have. You can add
-attributes to a class (not to individual objects) like so:
+=head2 How do I access attributes?
- addattribute $P0, "legs"
+Attributes can be access by a short name, fully qualified name or by index.
-=head2 How do I access attributes?
+ $P0 = getattribute self, "legs"
+ assign $P0, 4 # set attribute's value
-Attributes can be access by a fully qualified name or by index.
+or
$P0 = getattribute self, "Animal\0legs"
assign $P0, 4 # set attribute's value
@@ -326,7 +384,17 @@ add more parent classes to it with the C
=head2 How can I specify the constructor of a class?
-You can specify the constructor method by setting the BUILD property of
+Just define a method named C<__init> in the namespace if the class.
+
+ newclass $P0, "Dog" # create a class named Dog
+ # ...
+
+ .namespace ["Dog"]
+
+ .sub __init method
+ # ...
+
+Or you can specify the constructor method by setting the BUILD property of
the class PMC:
newclass $P0, "Dog" # create a class named Dog
@@ -344,6 +412,10 @@ Then, you can create an instance of Dog
new $P0, $I0 # creates a Dog object and stores it in register $P0
+or for short:
+
+ new $P0, "Dog"
+
During the C<new> opcode the constructor is called.
=head2 How can I pass arguments to an constructor?
@@ -352,7 +424,7 @@ You can pass only a single argument to a
By convention, a hash PMC is passed to the constructor that contains
the arguments as key/value pairs:
- new $P0, .PerlHash
+ new $P0, .Hash
set $P0["greeting"], "hello"
set $P0["size"], 1.23
@@ -386,11 +458,11 @@ Not too hard, is it?
Use C<push_eh> to push an exception handler onto the stack.
push_eh handler
- $P0 = new Exception
- throw $P0
+ $P0 = new Exception # or any other code ...
+ throw $P0 # ... that might throw
clear_eh
exit 0
-
+
handler:
print "Exception caught!\n"
exit 1
@@ -405,7 +477,7 @@ P5 is the register used for the Exceptio
throw $P0
clear_eh
exit 0
-
+
handler:
print "Exception: "
$S0 = P5["_message"]
@@ -413,10 +485,31 @@ P5 is the register used for the Exceptio
print "\n"
exit 1
+=head1 Misc
+
+=head2 How can I access a programs environment.
+
+Create a new C<Env> PMC and access it like a hash.
+
+ .local pmc e
+ e = new .Env
+ $P0 = e['USER'] # lt
+
+=head2 How can I access parrot's configuration.
+
+ .include "iglobals.pasm"
+ .local pmc interp, cfg
+ interp = getinterp
+ cfg = interp[.IGLOBALS_CONFIG_HASH]
+ $S0 = cfg['VERSION'] "0.2.2"
+
+Seel F<config_lib.pasm> for all the keys in the config hash - or iterate
+over the config hash.
+
=head1 VERSION
=over 4
-=item Revision 0.4 - 28 June 2005
+=item Revision 0.5 - 2005.08.03
=back
