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+# This is a file defining the BP grammar using BP syntax
+#
+# This is a complete definition of the grammar of BP grammar files, but it's
+# mainly intended to be used as a proof-of-concept, and a stress-test for BP.
+# The grammar files provided with BP are not otherwise intended to be full
+# language grammars.
+
+Grammar: __ *(Def [__`;])%__ __ ($$ / @!=(..$$%\n => "Could not parse this code"))
+Def: @name=id __ `: __ (
+      @definition=extended-pat
+    / $$ @!=(''=>"No definition for rule")
+    / @!=(..>(`;/id_`:/$)%\n => "Invalid definition: @0"))
+
+# This is used for command line arguments:
+String-pattern: ..$$ % (\n / Nodent / Escape / `\ pat [`;])
+
+pat: simple-pat !(__("!="/"==")) / suffixed-pat
+simple-pat: Upto-and / Dot / String / Chars / Nodent / Escape-range
+    / Escape / Repeat / Optional / No / After / Before / Capture
+    / Ref / parens
+
+suffixed-pat: (
+      Eq-pat
+    / Not-eq-pat
+)
+
+Eq-pat: @first=pat__"=="__@second=pat
+Not-eq-pat: @first=pat__"!="__@second=pat
+
+Dot: `. !`.
+String: (
+        `" @s=*(Escape / !`".) (`" / @!=(''=> "Expected closing quote here"))
+      / `' @s=*(Escape / !`'.) (`' / @!=(''=> "Expected closing quote here"))
+    )
+Chars: `` @+(Char-range/Char) % `,
+Char-range: @low=. `- (@high=. / @!=(''=> "Expected a second character to form a character range"))
+Char: (@s=. / @!=(''=> "Expected a character following the '`'"))
+Escape-range: `\ @low=escape-sequence `- @high=escape-sequence
+Escape: `\ (@s=escape-sequence
+    / $ @!=(''=>"Backslashes are used for escape sequences, not splitting lines")
+    / @!=(. *(Abc/`0-9) => "Invalid escape sequence: '@0'")
+)
+escape-sequence: (
+       `n,t,r,e,b,a,v
+      / 1-3 `0-7
+      / `x 2 `0-9,a-f,A-F
+    )
+No: `! (__@pat / @!=(''=>"Expected a pattern after the exclamation mark"))
+Nodent: `\ `N
+Upto-and: ".." [__@first=simple-pat] [__`%__@second=simple-pat]
+Repeat: (
+        @min=(''=>'0') (`*=>"-") @max=(''=>'∞')
+      / @min=int __ `- __ @max=int
+      / @min=(int / ''=>'1') __ (`+=>"-") @max=(''=>'∞')
+      / @min=@max=int
+    ) __ @repeat-pat=pat [__`%__@sep=pat]
+Optional: `[ __ extended-pat (__`] / @!=(''=> "Expected closing square bracket here"))
+After: `< __ pat
+Before: `> __ pat
+Capture: `@ [__ @capture-name=(id/`!) __ !"=>" `=] __ (@capture=pat / @!=(''=> "Expected pattern to capture"))
+Replace: (
+      @replace-pat=(Replace / Chain / pat) __ "=>" (__ @replacement=String / @!=(''=> "Expected replacement string"))
+    )
+Ref: @name=id !(__`:)
+
+parens: `( __ extended-pat (__ `) / @!=(''=> "Expected closing parenthesis here"))
+
+Chain: 2+@(pat !(__"=>") / Replace)%__
+Otherwise: 2+@(Replace / Chain / pat)%(__`/__)
+extended-pat: Otherwise / Replace / Chain / pat
+
+# Special-symbol rules:
+_:  *(`  / \t)
+__: *(`  / \t / \r / \n / comment)
+$$: !(./\n)
+$:  !.
+^^: !<(./\n)
+^:  !<.
+
+id: "^^" / "^" / "__" / "_" / "$$" / "$" / "|" / `a-z,A-Z *`a-z,A-Z,0-9,-
+
+comment: `# .. $