A. Q Language Grammar

This appendix summarizes the syntactical rules of the Q language. Please refer to Lexical Matters, for a detailed discussion of lexical matters. The syntax rules are given in BNF with the following extensions:

{ } denotes repetition; the enclosed elements may be repeated zero or more times.
[ ] denotes optional parts; the enclosed elements may be omitted.

The left-hand and right-hand sides of syntax rules are separated with a colon, and the | symbol denotes different alternatives. Identifiers stand for nonterminal grammar symbols, and terminal symbols are enclosed in single quotes.

In order to keep the grammar to a reasonable size, it does not specify the precedence of operator symbols. Expressions are parsed according to the precedence and associativity of operator symbols specified in Built-In Operators. A `=' symbol occuring unparenthesized in an equation separates left- and right-hand side.

script                  : {declaration|definition}

declaration             : unqualified-import
                        | qualified-import

                        | prefix headers ';'
                        | [scope] 'type' unqualified-identifier
                          [':' identifier] ['=' sections] ';'
                        | [scope] 'extern' 'type' unqualified-identifier
                          [':' identifier] ['=' sections] ';'
                        | [scope] 'type' qualified-identifier
                          ['as' unqualified-identifier] ';'
                        | [scope] 'type' unqualified-identifier
                          '==' identifier ';'

                        | '@' ['+'|'-'] unsigned-number

unqualified-import      : 'import' module-spec {',' module-spec} ';'
                        | 'include' module-spec {',' module-spec} ';'

qualified-import        : 'from' module-spec 'import' [symbol-specs] ';'
                        | 'from' module-spec 'include' [symbol-specs] ';'

module-spec             : module-name ['as' unqualified-identifier]
module-name             : unqualified-identifier
                        | string

symbol-specs            : symbol-spec {',' symbol-spec}

symbol-spec             : unqualified-identifier ['as' unqualified-identifier]
                        | unqualified-opsym ['as' unqualified-opsym]

prefix                  : scope
                        | [scope] modifier {modifier}

scope                   : 'private'|'public'

modifier                : 'const'|'special'|'extern'|'var'|'virtual'

headers                 : header {',' header}

header                  : unqualified-identifier '=' expression
                        | unqualified-identifier
                          {['~'] variable-identifier}
                        | qualified-identifier
                          {['~'] variable-identifier}
                          ['as' unqualified-identifier]
                        | '(' unqualified-opsym ')'
                          {['~'] variable-identifier}
                          ['@' precedence]
                        | '(' qualified-opsym ')'
                          {['~'] variable-identifier}
                          ['@' precedence]
                          ['as' unqualified-opsym]

precedence              : unsigned-number
                        | '(' operator ')'

sections                : section {'|' section}

section                 : [prefix] headers

definition              : expression
                          lqualifiers '=' expression qualifiers ';'
                          {lqualifiers '=' expression qualifiers ';'}
                        | 'def' expression '=' expression
                          {',' expression '=' expression} ';'
                        | 'undef' identifier {',' identifier} ';'

lqualifiers             : [qualifier {qualifier} ':']

qualifiers              : {qualifier}

qualifier               : condition
                        | where-clause

condition               : 'if' expression
                        | 'otherwise'

where-clause            : 'where' expression '=' expression
                          {',' expression '=' expression}

expression              : identifier
                        | 'var' unqualified-identifier
                        | variable-identifier ':' identifier
                        | number
                        | string
                        | expression expression
                        | unary-op expression
                        | expression binary-op expression
                        | 'if' expression 'then' expression
                          ['else' expression]
                        | '\' expression { expression } '.' expression
                        | '(' [element-list|enumeration|comprehension] ')'
                        | '[' [element-list|enumeration|comprehension] ']'
                        | '{' [element-list|enumeration|comprehension] '}'
                        | '(' op ')'
                        | '(' expression binary-op ')'
                        | '(' binary-op expression ')'

element-list            : expression-list [',' | ';' | '|' expression]

enumeration             : expression-list '..' [expression]

comprehension           : expression ':' expression-list

expression-list         : expression {',' expression}
                        | expression {';' expression}

identifier              : unqualified-identifier
                        | qualified-identifier

qualified-identifier    : module-identifier '::'
                          unqualified-identifier
unqualified-identifier  : variable-identifier
                        | function-identifier
                        | type-identifier

module-identifier       : letter {letter|digitsym}
type-identifier         : letter {letter|digitsym}
variable-identifier     : uppercase-letter {letter|digitsym}
                        | '_'
function-identifier     : lowercase-letter {letter|digitsym}

op                      : unary-op|binary-op

unary-op                : opsym
binary-op               : opsym|'and' 'then'|'or' 'else'

opsym                   : unqualified-opsym
                        | qualified-opsym

qualified-opsym         : module-identifier '::'
                          unqualified-opsym
unqualified-opsym       : function-identifier
                        | punctsym {punctsym}

number                  : ['-'] unsigned-number
unsigned-number         : '0' octdigitseq
                        | '0x' hexdigitseq
                        | '0X' hexdigitseq
                        | digitseq ['.' [digitseq]] [scalefact]
                        | [digitseq] '.' digitseq [scalefact]

digitseq                : digit {digit}
octdigitseq             : octdigit {octdigit}
hexdigitseq             : hexdigit {hexdigit}

scalefact               : 'E' ['-'] digitseq
                        | 'e' ['-'] digitseq

string                  : '"' {char} '"'

letter                  : uppercase-letter|lowercase-letter
uppercase-letter        : 'A'|...|'Z'|uppercase unicode letter
lowercase-letter        : 'a'|...|'z'|'_'|lowercase unicode letter
digitsym                : '0'|...|'9'|unicode digit
punctsym                : unicode punctuation character

digit                   : '0'|...|'9'
octdigit                : '0'|...|'7'
hexdigit                : '0'|...|'9'|'a'|...|'f'|'A'|...|'F'

char                    : any character but newline and "

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