use ABNF for the grammar specification instead

ABNF has a more accepted standard than EBNF.

docs/grammar.abnf

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+; Rutile's grammar formal definition in ABNF
+; NOTE: terminal strings are case sensitive here
+
+function_kind 	 = "proc" / "iter"
+proc_decl 		 = function_kind "(" [proc_decl_args] ")" [ident] *stmt 'end'
+proc_decl_args 	 = symbol_type_pair *("," symbol_type_pair)
+symbol_type_pair = ident ":" ident
+
+symbol_decl = ("var" / "let" / "const") ident_type_expr		; "Variable" declaration
+ident_type_expr = ident [":" ident] ["=" expr]
+
+function_call = ident_qualified "(" [funcargs] ")"
+funcargs      = expr_list
+
+array_literal = "[" expr_list "]"
+
+expr_list 	= expr *("," expr) [","]					; Allows a trailling comma
+expr 		=  number
+expr		=/ array_literal
+expr		=/ function_call
+
+pragma = "#" "["  "]"								; TODO
+decorated_decl = pragma (proc_decl / symbol_decl)
+
+; Statements
+while_stmt 		= "while" expr *stmt "end"
+if_expr 		= "if" expr *stmt "end"
+break_expr 		= "break" *expr
+return_stmt 	= "return" *expr
+yield_stmt 		= "yield" *expr
+loop_control 	= "next" / break_expr
+stmt 			=  proc_decl
+stmt 			=/ expr
+stmt 			=/ loop_control
+stmt 			=/ if_expr
+stmt 			=/ while_stmt
+stmt 			=/ return_stmt
+stmt 			=/ yield_stmt
+
+ident = (ALPHA / "_") *(ALPHA / DIGIT / "_" / "?" / "!")
+; Identifier accounting for namespacing: std:io.print, aaa:bbb:ccc
+ident_qualified = (ALPHA / "_") *(ALPHA / DIGIT / "_" / "?" / "!" / ":" / ".")
+
+number 	= 1*DIGIT				; Decimal
+		/ "0b" 1*("0" / "1")	; Binary
+		/ "0o" 1*(0-8)			; Octal
+		/ "0x" 1*HEXDIGIT 		; Hexadecimal
+
+byte			= %x00-FF
+escape 			= "\" ("\" / DQUOTE / "0" / "a" / "b" / "n" / "r" / "t" / ("x" 1*2HEXDIGIT))
+character		= byte / escape
+string_literal 	= DQUOTE *character DQUOTE