Add current grammar

README.md

@@ -19,39 +19,63 @@ and a possbility to compile Elna programs for different platforms.
 
 ## Grammar
 
+```ebnf
 digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9";
+letter = "A" | "B" | … | "Z" | "a" | "b" | … | "z";
 
+ident = letter { letter | digit | "_" };
 integer = digit { digit };
+float = integer "." integer;
 boolean = "true" | "false";
 
 program = [ "type" type_definitions ";" ]
-    [ "const" ident "=" integer { "," ident "=" integer } ";"]
+    [ constant_part ]
     { procedure_definition }
-    [ "var" variable_declarations ";" ]
+    [ variable_part ]
     compound_statement ".";
 
-procedure_definition = "procedure" ident formal_parameter_list ";" block ";";
+procedure_definition = "proc" ident formal_parameter_list ";" block ";";
 
-block = [ "const" ident "=" integer { "," ident "=" integer } ";" ]
-    [ "var" variable_declarations ";" ]
+block = [ constant_part ]
+    [ variable_part ]
     statement;
 
-statement = [ ident ":=" expression
-            | ident actual_parameter_list
-            | compound_statement
-            | "if" condition "then" statement 
-            | "while" condition "do" statement ];
+constant_part = "const" ident "=" integer { "," ident "=" integer } ";";
+variable_part = "var" variable_declarations ";";
 
-compound_statement = "begin" statement {";" statement } "end" ;
+statement = compound_statement
+          | ident ":=" expression
+          | ident actual_parameter_list
+          | "while" condition "do" statement
+          | "if" expression "then" statement [ else statement ];
+
+statement_list = statement {";" statement };
+compound_statement = "begin" [ statement_list ] "end";
 
 condition = "odd" expression |
             expression ("="|"#"|"<"|"<="|">"|">=") expression;
 
-expression = [ "+"|"-"] term { ("+"|"-") term};
+comparison_operator = "=", "/=", "<", ">", "<=", ">=";
+unary_prefix = "not", "@";
 
-term = factor { ("*"|"/") factor };
+expression = logical_operand { ("and" | "or") logical_operand };
+logical_operand = comparand { comparison_operator comparand };
+comparand = summand { ("+" | "-") summand };
+summand = factor { ("*" | "/") factor };
+factor = pointer { unary_prefix pointer };
 
-factor = ident | integer | "(" expression ")";
+pointer = integer
+        | float
+        | boolean
+        | "'" character "'"
+        | """ { character } """
+        | designator_expression { $$ = $1; }
+        | "(" expression ")";
+
+designator_expression = designator_expression "[" expression "]"
+                      | designator_expression "." ident
+                      | designator_expression "^"
+                      | ident;
 
 formal_parameter_list = "(" [ variable_declarations ] ")";
 
@@ -71,3 +95,4 @@ type_expression = "array" integer "of" type_expression
 field_list = field_declaration { ";" field_declaration };
 
 field_declaration = ident ":" type_expression;
+```