Version: 0.4.4

KCL Spec

Lexical rules

Keywords and reserved words

The following are the keywords of the KCL:

    True       False      None        Undefined   import
    and        or         in          is          not
    as         if         else        elif        for
    schema     mixin      protocol    check       assert
    all        any        map         filter      lambda
    rule

The following are reserved words for the KCL:

    pass       return     validate   rule        flow
    def        del        raise      except      try
    finally    while      from       with        yield
    global     nonlocal   struct     class       final

Line comment

# a comment

Operators

    +       -       *       **      /       //      %
    <<      >>      &       |       ^       <       >
    ~       <=      >=      ==      !=      =
    +=      -=      *=      **=     /=      //=     %=
    <<=     >>=     &=      ^=

Delimiters

    (       )       [       ]       {       }
    ,       :       .       ;       @

Operator precedence

The following list of operators is ordered from highest to lowest:

Operator	Description
`**`	Exponentiation (highest priority)
`+x` `-x` `~x`	Positive, negative, bitwise NOT
`*` `/` `%` `//`	Multiplication, division, floor division and remainder
`+` `-`	Addition and subtraction
`<<` `>>`	Left and right shifts
`&`	Bitwise AND
`^`	Bitwise XOR
\|	Bitwise OR
`in`, `not in`, `is`, `is not`, `<`, `<=`, `>`, `>=`, `!=`, `==`	Comparisons, including membership and identity operators
`not`	Boolean NOT
`and`	Boolean AND
`or`	Boolean OR
`if – else`	Conditional expression =
`=`, `+=`, `-=`, `=`, `/=`, `%=`, `&=`, `=`, `^=`, `\\*=`, `//=`, `<<=`, `>>=`	Assign

Grammar

KCL uses Python's LarkParser tool to describe the grammar, and the specification rules are as follows:

// Copyright 2021 The KCL Authors. All rights reserved.

//////////// KCL grammar ////////////
start: (NEWLINE | preamble_statement)*

//////////// statement ////////////
preamble_statement: preamble_small_stmt | preamble_compound_stmt
preamble_small_stmt: (small_stmt | import_stmt) NEWLINE
preamble_compound_stmt: compound_stmt | schema_stmt
statement: small_stmt NEWLINE | compound_stmt
compound_stmt: if_stmt
small_stmt: assign_stmt | expr_stmt | assert_stmt

//////////// import_stmt ////////////
import_stmt: IMPORT dot_name (AS NAME)?
dot_name: [leading_dots] identifier (DOT identifier)*
leading_dots: DOT+

/////////// assert_stmt ////////////
assert_stmt: ASSERT test (COMMA test)?

//////////// if_stmt ////////////
if_stmt: IF test COLON suite (ELIF test COLON suite)* (ELSE COLON suite)?
suite: small_stmt NEWLINE | NEWLINE _INDENT statement+ _DEDENT

//////////// assign_stmt ////////////
assign_stmt: primary_expr (ASSIGN primary_expr)* ASSIGN test
    | primary_expr augassign test
augassign: COMP_PLUS | COMP_MINUS | COMP_MULTIPLY | COMP_DOUBLE_STAR | COMP_DIVIDE
    | COMP_DOUBLE_DIVIDE | COMP_MOD | COMP_AND | COMP_OR | COMP_XOR | COMP_SHIFT_LEFT
    | COMP_SHIFT_RIGHT

//////////// schema_stmt ////////////
schema_stmt: [decorators] SCHEMA [RELAXED] identifier [LEFT_BRACKETS [arguments] RIGHT_BRACKETS] [LEFT_PARENTHESES operand_name RIGHT_PARENTHESES] COLON NEWLINE [schema_body]
schema_body: _INDENT (string NEWLINE)* [mixin_stmt] (schema_attribute_stmt | statement)* [check_block] _DEDENT
schema_attribute_stmt: [decorators] (FINAL)? identifier COLON type [(ASSIGN | augassign) test] NEWLINE

/////////// decorators ////////////
decorators: (AT primary_expr NEWLINE)+

//////////// type ////////////
type: type_element (OR type_element)*
type_element: schema_type | basic_type | compound_type
schema_type: operand_name
basic_type: STRING_TYPE | INT_TYPE | FLOAT_TYPE | BOOL_TYPE
compound_type: list_type | dict_type
list_type: LEFT_BRACKETS (type)? RIGHT_BRACKETS
dict_type: LEFT_BRACE (type)? COLON (type)? RIGHT_BRACE

//////////// check_block ////////////
check_block: CHECK COLON NEWLINE _INDENT check_expr+ _DEDENT
check_expr: check_test [COMMA primary_expr] NEWLINE
check_test: or_test [IF or_test]

//////////// mixin_stmt ////////////
mixin_stmt: MIXIN LEFT_BRACKETS [mixins | multiline_mixins] RIGHT_BRACKETS NEWLINE
multiline_mixins: NEWLINE _INDENT mixins NEWLINE _DEDENT
mixins: operand_name (COMMA (NEWLINE mixins | operand_name))*

//////////// expression_stmt ////////////
expr_stmt: expression
expression: test (COMMA test)*
test: if_expr | primary_expr | unary_expr | binary_expr
if_expr: test IF test ELSE test
unary_expr: (PLUS | MINUS | NOT) primary_expr | L_NOT test
binary_expr: test bin_op test
bin_op: L_OR
      | L_AND
      | EQUAL_TO | NOT_EQUAL_TO | LESS_THAN | GREATER_THAN | LESS_THAN_OR_EQUAL_TO | GREATER_THAN_OR_EQUAL_TO
      | IN | L_NOT IN | IS | IS L_NOT
      | OR
      | XOR
      | AND
      | MINUS | PLUS
      | MULTIPLY | MOD | DIVIDE | DOUBLE_DIVIDE
      | SHIFT_LEFT | SHIFT_RIGHT

primary_expr: operand | primary_expr select_suffix | primary_expr call_suffix | primary_expr subscript_suffix | primary_expr schema_expr
operand: operand_name | number | string
    | TRUE | FALSE | NONE | list_expr | list_comp | dict_expr
    | dict_comp | LEFT_PARENTHESES test RIGHT_PARENTHESES
operand_name: identifier | qualified_identifier

select_suffix: DOT (identifier | dict_identifier_selector | list_identifier_selector)
dict_identifier_selector: MULTIPLY | LEFT_BRACE identifier (COMMA identifier)* RIGHT_BRACE
list_identifier_selector: subscript_suffix

//////////// call_suffix ////////////
call_suffix: LEFT_PARENTHESES [arguments [COMMA]] RIGHT_PARENTHESES

//////////// subscript_suffix ////////////
subscript_suffix: LEFT_BRACKETS (test | [test] COLON [test] [COLON [test]]) RIGHT_BRACKETS

//////////// arguments ////////////
arguments: argument (COMMA argument)*
argument: test | NAME ASSIGN test | MULTIPLY test | DOUBLE_STAR test


//////////// operand ////////////
identifier: NAME
qualified_identifier: identifier DOT identifier

//////////// list_expr ////////////
list_expr: LEFT_BRACKETS [list_items | NEWLINE _INDENT list_items _DEDENT] RIGHT_BRACKETS
list_items: list_item ((COMMA [NEWLINE] | NEWLINE) list_item)* [COMMA] [NEWLINE]
list_item: test | star_expr
list_comp: LEFT_BRACKETS (list_item comp_clause+ | NEWLINE _INDENT list_item comp_clause+ _DEDENT) RIGHT_BRACKETS
//////////// dict_expr ////////////
dict_expr: LEFT_BRACE [entries | NEWLINE _INDENT entries _DEDENT] RIGHT_BRACE
dict_comp: LEFT_BRACE (entry comp_clause+ | NEWLINE _INDENT entry comp_clause+ _DEDENT) RIGHT_BRACE
entries: entry ((COMMA [NEWLINE] | NEWLINE) entry)* [COMMA] [NEWLINE]
entry: test COLON test | double_star_expr
comp_clause: FOR loop_variables [COMMA] IN or_test [NEWLINE] [IF test [NEWLINE]]

star_expr: MULTIPLY primary_expr
double_star_expr: DOUBLE_STAR primary_expr
loop_variables: primary_expr (COMMA primary_expr)*

//////////// schema_expr ////////////
schema_expr: (LEFT_PARENTHESES [arguments] RIGHT_PARENTHESES)? dict_expr

//////////// misc ////////////
number: DEC_NUMBER | HEX_NUMBER | BIN_NUMBER | OCT_NUMBER | FLOAT_NUMBER | IMAG_NUMBER
string: STRING | LONG_STRING

// Tokens

ASSIGN: "="
COLON: ":"
SEMI_COLON: ";"
COMMA: ","
LEFT_PARENTHESES: "("
RIGHT_PARENTHESES: ")"
LEFT_BRACKETS: "["
RIGHT_BRACKETS: "]"
LEFT_BRACE: "{"
RIGHT_BRACE: "}"
PLUS: "+"
MINUS: "-"
MULTIPLY: "*"
DIVIDE: "/"
MOD: "%"
DOT: "."
AND: "&"
OR: "|"
XOR: "^"
NOT: "~"
LESS_THAN: "<"
GREATER_THAN: ">"
EQUAL_TO: "=="
NOT_EQUAL_TO: "!="
GREATER_THAN_OR_EQUAL_TO: ">="
LESS_THAN_OR_EQUAL_TO: "<="
DOUBLE_STAR: "**"
DOUBLE_DIVIDE: "//"
SHIFT_LEFT: "<<"
SHIFT_RIGHT: ">>"
AT: "@"

COMP_PLUS: "+="
COMP_MINUS: "-="
COMP_MULTIPLY: "*="
COMP_DIVIDE: "/="
COMP_MOD: "%="
COMP_AND: "&="
COMP_OR: "|="
COMP_XOR: "^="
COMP_DOUBLE_STAR: "**="
COMP_DOUBLE_DIVIDE: "//="
COMP_SHIFT_LEFT: "<<="
COMP_SHIFT_RIGHT: ">>="

// Special tokens
IMPORT: "import"
AS: "as"
SCHEMA: "schema"
MIXIN: "mixin"
RELAXED: "relaxed"
CHECK: "check"
FOR: "for"
ASSERT: "assert"
IF: "if"
ELIF: "elif"
ELSE: "else"
L_OR: "or"
L_AND: "and"
L_NOT: "not"
IN: "in"
IS: "is"
FINAL: "final"
LAMBDA: "lambda"

STRING_TYPE: "str"
INT_TYPE: "int"
FLOAT_TYPE: "float"
BOOL_TYPE: "bool"

// Constant tokens
TRUE: "True"
FALSE: "False"
NONE: "None"

NAME: /[a-zA-Z_]\w*/
COMMENT: /#[^\n]*/
NEWLINE: ( /\r?\n[\t ]*/ | COMMENT )+

STRING: /[ubf]?r?("(?!"").*?(?<!\\)(\\\\)*?"|'(?!'').*?(?<!\\)(\\\\)*?')/i
LONG_STRING: /[ubf]?r?(""".*?(?<!\\)(\\\\)*?"""|'''.*?(?<!\\)(\\\\)*?''')/is

DEC_NUMBER: /\-?0|\-?[1-9]\d*/i
HEX_NUMBER.2: /\-?0[xX][0-9a-fA-F]+/i
OCT_NUMBER.2: /\-?0[oO][0-7]+/i
BIN_NUMBER.2 : /\-?0[bB][0-1]+/i
FLOAT_NUMBER.2: /(([-+]?\d+\.\d*|\.\d+)(e[-+]?\d+)?|\d+(e[-+]?\d+))/i
IMAG_NUMBER.2: /\d+j/i | FLOAT_NUMBER "j"i

%ignore /[\t \f]+/  // WS
%ignore /\\[\t \f]*\r?\n/   // LINE_CONT
%declare _INDENT _DEDENT

Lexical rules​

Keywords and reserved words​

Line comment​

Operators​

Delimiters​

Operator precedence​

Grammar​