Polyp = { Statement ";" } .

Statement = Declaration | Call .

Declaration = VariableDeclaration | FunctionDeclaration .

VariableDeclaration = [ "var" ] VariableList  ":=" ExpressionList .
FunctionDeclaration = [ "def" ] Function ":=" Expression .

VariableList = variable { "," variable } .
ExpressionList = Expression { "," Expression } .

// ForLoop = "for" Condition Block .

// Block = "{" Polyp "}" .

Function = identifier Parameters .
Parameters = "(" [ ParameterList ] ")" .
ParameterList = variable { "," variable } .

Call = identifier "(" [ ExpressionList ] ")" .
BuiltinCall = identifier "(" [ ExpressionList ] ")" .

Expression = Expr { log_op Expr } .

Expr = UnaryExpr | Expr binary_op UnaryExpr .

UnaryExpr = [ "(" ] PrimaryExpr [ ")" ] | unary_op [ "(" ] PrimaryExpr [ ")" ] .

PrimaryExpr = BuiltinCall | Call | Expr | Operand .

Operand = Literal | identifier .
Literal = int_lit | float_lit .

binary_op = rel_op | math_op .
log_op = "|" | "&" .
rel_op = "=" | "!=" | "<" | ">" | "<=" | ">=" | "<>" .
math_op = "+" | "-" | "*" | "/" | "%" | "^" | "**" .
unary_op = "+" | "-" | "!" | "¬" | "~" .

// Boolean = true | false .
// true = "True" .
// false = "False" .
// none = "None" .

variable = identifier .

identifier = letter { letter | unicode_digit } .

unicode_letter = "a" ... "z" | "A" ... "Z" .
unicode_digit = decimal_digit .
letter        = unicode_letter | "_" .
decimal_digit = "0" ... "9" .
octal_digit   = "0" ... "7" .
hex_digit     = "0" ... "9" | "A" ... "F" | "a" ... "f" .

int_lit     = decimal_lit | octal_lit | hex_lit .
decimal_lit = ( "1" ... "9" ) { decimal_digit }  | "0" .
octal_lit   = "0" octal_digit { octal_digit } .
hex_lit     = "0" ( "x" | "X" ) hex_digit { hex_digit } .

float_lit = decimals "." [ decimals ] [ exponent ] |
            decimals exponent |
            "." decimals [ exponent ] |
            [ "+" | "-" ] "nan" | [ "+" | "-" ] "inf" .
decimals  = decimal_digit { decimal_digit } .
exponent  = ( "e" | "E" ) [ "+" | "-" ] decimals .

// char_lit         = "'" ( unicode_value | byte_value ) "'" .
// unicode_value    = unicode_char | little_u_value | big_u_value | escaped_char .
// byte_value       = octal_byte_value | hex_byte_value .
// octal_byte_value = `\` octal_digit octal_digit octal_digit .
// hex_byte_value   = `\` "x" hex_digit hex_digit .
// little_u_value   = `\` "u" hex_digit hex_digit hex_digit hex_digit .
// big_u_value      = `\` "U" hex_digit hex_digit hex_digit hex_digit
//                           hex_digit hex_digit hex_digit hex_digit .
// escaped_char     = `\` ( "a" | "b" | "f" | "n" | "r" | "t" | "v" | `\` | "'" | `"` ) .

// StringLit              = string_lit { string_lit } .
// string_lit             = raw_string_lit | interpreted_string_lit .
// raw_string_lit         = "`" { unicode_char } "`" .
// interpreted_string_lit = `"` { unicode_value | byte_value } `"` .