slangs, what are they?

COBOL.pm

class COBOL does Slangy {
    has $.grammar = grammar {
        token TOP { .* }
    };
    has $.actions = class {
        method TOP($/) { say "method TOP($/)" }
    }
}

in-short.md

I'd imagine that the following could be the nicest way to create your own slang:

# The `slang` keyword implicitly applies "does Slangy" which stubs `has $.grammar;`
# and `has $.actions;`. It also makes sure the slang will be available as `$~COBOL`
# and the grammar and actions will be put in `%*LANG`.
slang COBOL {
    has $.grammar = COBOL::Grammar.new;
    has $.actions = COBOL::Actions.new;

    # Optionally register our own module loader to support `use Foo:from<COBOL`
    # from within Perl 6.
    has $.module-loader = COBOL::ModuleLoader;
}

# Or register the ML later, by:
$~COBOL.module-loader = COBOL::ModuleLoader.new;

rakudo.diff

diff --git a/src/Perl6/Grammar.nqp b/src/Perl6/Grammar.nqp
index a37b6ec..69e0d3e 100644
--- a/src/Perl6/Grammar.nqp
+++ b/src/Perl6/Grammar.nqp
@@ -854,6 +854,7 @@ grammar Perl6::Grammar is HLL::Grammar does STD {
         
         # Quasis and unquotes
         :my $*IN_QUASI := 0;                       # whether we're currently in a quasi block
+        :my $*MAIN := 'MAIN';
 
         # Setting loading and symbol setup.
         {
@@ -922,6 +923,9 @@ grammar Perl6::Grammar is HLL::Grammar does STD {
                     %*LANG{$_.key} := $_.value;
                 }
             }
+            if $have_outer && $*UNIT_OUTER.symbol('$*MAIN') {
+                $*MAIN := $*UNIT_OUTER.symbol('$*MAIN')<value>;
+            }
             
             # Install unless we've no setting, in which case we've likely no
             # static lexpad class yet either. Also, UNIT needs a code object.
@@ -944,7 +948,7 @@ grammar Perl6::Grammar is HLL::Grammar does STD {
         
         <.finishpad>
         <.bom>?
-        <statementlist>
+        <statementlist=.LANG($*MAIN, 'statementlist')>
 
         <.install_doc_phaser>
         
@@ -1257,13 +1261,23 @@ grammar Perl6::Grammar is HLL::Grammar does STD {
 
     token statement_control:sym<use> {
         :my $longname;
+        :my $module;
         :my $*IN_DECL := 'use';
         :my $*HAS_SELF := '';
         :my $*SCOPE   := 'use';
+        :my $OLD_MAIN := ~$*MAIN;
         $<doc>=[ 'DOC' \h+ ]**0..1
         <sym> <.ws>
         [
-        | <version>
+        | <version> [ <?{ ~$<version><vnum>[0] eq '5' }> {
+                        $module := $*W.load_module($/, 'Perl5', {}, $*GLOBALish);
+                        do_import($/, $module, 'Perl5');
+                        $longname := 'Perl5';
+                        $/.CURSOR.import_EXPORTHOW($module);
+                    } ]?
+                    [ <?{ ~$<version><vnum>[0] eq '6' }> {
+                        $*MAIN := 'MAIN';
+                    } ]?
         | <module_name>
             {
                 $longname := $<module_name><longname>;
@@ -1296,7 +1310,7 @@ grammar Perl6::Grammar is HLL::Grammar does STD {
                             $<arglist><EXPR>.ast);
                     $arglist    := nqp::getattr($arglist.list.eager,
                             $*W.find_symbol(['List']), '$!items');
-                    my $module  := $*W.load_module($/, $name, %cp, $*GLOBALish);
+                    $module  := $*W.load_module($/, $name, %cp, $*GLOBALish);
                     do_import($/, $module, $name, $arglist);
                     $/.CURSOR.import_EXPORTHOW($module);
                 }
@@ -1306,7 +1320,7 @@ grammar Perl6::Grammar is HLL::Grammar does STD {
                             my $lnd    := $*W.dissect_longname($longname);
                             my $name   := $lnd.name;
                             my %cp     := $lnd.colonpairs_hash('use');
-                            my $module := $*W.load_module($/, $name, %cp, $*GLOBALish);
+                            $module := $*W.load_module($/, $name, %cp, $*GLOBALish);
                             do_import($/, $module, $name);
                             $/.CURSOR.import_EXPORTHOW($module);
                         }
@@ -1314,6 +1328,17 @@ grammar Perl6::Grammar is HLL::Grammar does STD {
                 }
             ]
         ]
+        [
+        ||  <?{ nqp::defined($module) && nqp::existskey($module, ~$longname)
+                && nqp::istype($module{~$longname}, $*W.find_symbol(['Slangy'])) }>
+            {
+                $*MAIN                := ~$longname;
+                %*LANG<COBOL>         := $module{~$longname}.new.grammar;
+                %*LANG<COBOL-actions> := $module{~$longname}.new.actions;
+            }
+            <statementlist=.LANG($*MAIN, 'TOP')>
+        || <?>
+        ]
         <.ws>
     }
     
diff --git a/src/core/Positional.pm b/src/core/Positional.pm
index ac73982..bd764fd 100644
--- a/src/core/Positional.pm
+++ b/src/core/Positional.pm
@@ -1,3 +1,7 @@
 my role Positional[::T = Mu] {
     method of() { T }
 }
+
+my role Slangy[::T = Mu] {
+    method of() { T }
+}
diff --git a/src/core/core_prologue.pm b/src/core/core_prologue.pm
index e41cc40..3c24c95 100644
--- a/src/core/core_prologue.pm
+++ b/src/core/core_prologue.pm
@@ -4,6 +4,7 @@ use Perl6::BOOTSTRAP;
 my class Pair { ... }
 my class Whatever { ... }
 my class WhateverCode { ... }
+my role Slangy { ... }
 
 # Stub these or we can't use any sigil other than $.
 my role Positional { ... }

use-cobol.sh

$ perl6-p -I. -e 'use COBOL'
method TOP()
===SORRY!===
Can not get attribute '$!pos' declared in class 'NQPCursor' with this object

# Problem is that the Perl6 grammar is a NQP class, while our COBOL grammar is from Perl 6 land.
# We need to ross that boundary somehow...


$ perl6-p -I. -e 'use COBOL; hurz'
===SORRY!===
No such method 'substr' for invocant of type 'String'