Updated syntax definition

Author: DigitalFlow

README.md

@@ -877,13 +877,9 @@ This E-Mail was automatically generated by the system.
 The language syntax is defined by the following BNF (Backus-Naur form):
 
 ```
-<function_call> ::= <whitespace>* <function_name> <whitespace>* "(" <whitespace>* <arguments>? <whitespace>* ")" <whitespace>*
-
-<function_name> ::= <identifier>
+<formula> ::= <number> | <string> | <boolean> | <object> | <list> | <null> | <lambda_function> | <function_call>
 
-<arguments> ::= <argument> | <argument> <whitespace>* "," <whitespace>* <arguments>
-
-<argument> ::= <number> | <string> | <boolean> | <object> | <list> | <lambda_function> | <function_call> | <identifier>
+<expression> ::= <formula> | <identifier> 
 
 <number> ::= <sign>? (<integer> | <floating_point>)
 
@@ -895,23 +891,43 @@ The language syntax is defined by the following BNF (Backus-Naur form):
 
 <float_suffix> ::= "d" | "m"
 
-<string> ::= "\"" <character>* "\"" | "'" <character>* "'"
+<string> ::= "\"" <double_quote_character>* "\"" | "'" <single_quote_character>* "'"
+
+<single_quote_character> ::= <character> | <double_quote> | <escaped_single_quote>
+
+<double_quote_character> ::=  <character> | <single_quote> | <escaped_double_quote>
+
+<single_quote> ::= "'"
+
+<double_quote> ::= "\""
+
+<escaped_single_quote> ::= <escape_character> <single_quote>
+
+<escaped_double_quote> ::= <escape_character> <double_quote>
+
+<escape_character> ::= "\\"
 
 <boolean> ::= "true" | "false"
 
 <object> ::= "{" <whitespace>* <key_value_pairs>? <whitespace>* "}"
 
 <key_value_pairs> ::= <key_value_pair> | <key_value_pair> <whitespace>* "," <whitespace>* <key_value_pairs>
 
-<key_value_pair> ::= <letter> <character>* <whitespace>* ":" <whitespace>* <value>
-
-<value> ::= <string> | <number> | <boolean> | <object> | <list> | <lambda_function> | <function_call> | <identifier>
+<key_value_pair> ::= <letter> <character>* <whitespace>* ":" <whitespace>* <expression>
 
 <list> ::= "[" <whitespace>* <list_elements>? <whitespace>* "]"
 
-<list_elements> ::= <argument> | <argument> <whitespace>* "," <whitespace>* <list_elements>
+<list_elements> ::= <expression> | <expression> <whitespace>* "," <whitespace>* <list_elements>
+
+<null> ::= "null"
+
+<function_call> ::= <whitespace>* <function_name> <whitespace>* "(" <whitespace>* <arguments>? <whitespace>* ")" <whitespace>*
+
+<function_name> ::= <identifier>
+
+<arguments> ::= <expression> | <expression> <whitespace>* "," <whitespace>* <arguments>
 
-<lambda_function> ::= <whitespace>* "(" <whitespace>* <parameter> <whitespace>* ")" <whitespace>* "=>" <whitespace>* <function_call> <whitespace>*
+<lambda_function> ::= <whitespace>* "(" <whitespace>* <parameter> <whitespace>* ")" <whitespace>* "=>" <whitespace>* <expression> <whitespace>*
 
 <parameter> ::= <identifier>
 
@@ -921,7 +937,7 @@ The language syntax is defined by the following BNF (Backus-Naur form):
 
 <letter> ::= "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" | "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"
 
-<character> ::= <letter> | <digit> | " " | "\"" | "!" | "#" | "$" | "%" | "&" | "'" | "(" | ")" | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | "=" | ">" | "?" | "@" | "[" | "]" | "^" | "_" | "`" | "{" | "|" | "}" | "~"
+<character> ::= <letter> | <digit> | " " | "!" | "#" | "$" | "%" | "&" | "(" | ")" | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | "=" | ">" | "?" | "@" | "[" | "]" | "^" | "_" | "`" | "{" | "|" | "}" | "~"
 
 <whitespace> ::= " " <whitespace>* | "\t" <whitespace>* | "\n" <whitespace>*
 ```