.ec e epsilon .am table_of_contents . bp . em .appendix "CLU Syntax" .para We use an extended BNF grammar to define the syntax. The general form of a production is: .show 4 .def nonterminal alternative .or alternative .or ```... .or alternative .eshow .para The following extensions are used: .nr fff fheight/4 .if . width "a , etc " . sv list_left_margin 800m . sv list_right_margin . sv list_indent width!m . sv list_space . sv list_spacing 1.5 . ilist a , etc stands for a list of one or more 2a*'s separated by commas; i.e., "a" or "a, a" or "a, a, a" etc. . next lcurly!arcurly stands for a sequence of zero or more 2a*'s; i.e., " " or "a" or "a a" etc. . next lbkt!arbkt stands for an optional 2a*; i.e., " " or "a". . end_list . en .para All semicolons are optional in CLU, but for simplicity they appear in the syntax as ";" rather than "lbkt!;rbkt". Nonterminal symbols appear in normal face. Reserved words appear in bold face. All other terminal symbols are non-alphabetic, and appear in normal face. .eq temp_or or .eq temp_def def .de bdef .be def_block .nv ls 110 .br .nv fill 0 .keep ndef \0 .hp d_stop0!m def .hp d_stop2!m .em . . .de or .br .hp d_stop1!m orbar .hp d_stop2!m .em . . .de ndef .end_keep .sp .5 .en .sr fff em look, ma! a space .if nargs>0 .sr fff .en .\fff!bdef \0 .em . . .de comment .sp .5 .hp d_stop1!m %  .em .de comment1 .br .hp d_stop1!m %  .em . . .de prec .hp percent_stop!m % .hp prec_stop!m \curprec .em . . .de nprec .nr curprec curprec-1 .nr prec_stop prec_stop+prec_width .prec .em . . .width "others_handler " .nr d_stop0 width .width "def" .nr d_stop1 d_stop0+(width/2) .width "cluster_body def " .nr d_stop2 width .width "expression // expression " .nr percent_stop d_stop2+width .width "% " .nr prec_width width . . .bdef module lcurly equate rcurly procedure .or lcurly equate rcurly iterator .or lcurly equate rcurly cluster . . .ndef procedure idn = s(1)proc lbkt parms rbkt args lbkt returns rbkt lbkt signals rbkt lbkt where rbkt ; t(1)body t(1)end idn ; . . .ndef iterator idn = s(1)iter lbkt parms rbkt args lbkt yields rbkt lbkt signals rbkt lbkt where rbkt ; t(1)body t(1)end idn ; . . .ndef cluster idn = s(1)cluster lbkt parms rbkt is idn , etc lbkt where rbkt ; t(1)cluster_body t(1)end idn ; . . .ndef parms [ parm , etc ] . . .ndef parm idn , etc : type .or idn , etc : type_spec . . .ndef args ( lbkt decl , etc rbkt ) . . .ndef decl idn , etc : type_spec . . .ndef returns returns ( type_spec , etc ) . . .ndef yields yields ( type_spec , etc ) . . .ndef signals signals ( exception , etc ) . . .ndef exception name lbkt ( type_spec , etc ) rbkt . . .ndef where where restriction , etc . . .ndef restriction idn has oper_decl , etc .or idn in type_set . . .ndef type_set { idn | idn has oper_decl , etc ; lcurly equate rcurly } .or idn . . .ndef oper_decl op_name , etc : type_spec . . .ndef op_name name lbkt [ constant , etc ] rbkt . . .ndef constant expression .or type_spec . . .ndef body lcurly equate rcurly lcurly statement rcurly . . .ndef cluster_body s(1)lcurly equate rcurly rep = type_spec ; lcurly equate rcurly b(1)routine lcurly routine rcurly . . .ndef routine procedure .or iterator . . .ndef equate idn = constant ; .or idn = type_set ; . . .ndef type_spec null .or bool .or int .or real .or char .or string .or any .or rep .or cvt .or array [ type_spec ] .or record [ field_spec , etc ] .or oneof [ field_spec , etc ] .or proctype ( lbkt type_spec , etc rbkt ) lbkt returns rbkt lbkt signals rbkt .or itertype ( lbkt type_spec , etc rbkt ) lbkt yields rbkt lbkt signals rbkt .or idn [ constant , etc ] .or idn . . .ndef field_spec name , etc : type_spec . . .ndef statement decl ; .or idn : type_spec := expression ; .or decl , etc := invocation ; .or idn , etc := invocation ; .or idn , etc := expression , etc ; .or primary . name := expression ; .or primary [ expression ] := expression ; .or invocation ; .or while expression do body end ; .or for lbkt decl , etc rbkt in invocation do body end ; .or for lbkt idn , etc rbkt in invocation do body end ; .or if s(1)expression then body t(1)lcurly elseif expression then body rcurly t(1)lbkt else body rbkt t(1)end ; .or tagcase expression t(1)tag_arm lcurly tag_arm rcurly t(1)lbkt others : body rbkt t(1)end ; .or return lbkt ( expression , etc ) rbkt ; .or yield lbkt ( expression , etc ) rbkt ; .or signal name lbkt ( expression , etc ) rbkt ; .or exit name lbkt ( expression , etc ) rbkt ; .or break ; .or continue ; .or begin body end ; .or statement except s(1)lcurly when_handler rcurly t(1)lbkt others_handler rbkt t(1)end ; . . .ndef tag_arm tag name , etc lbkt ( idn : type_spec ) rbkt : body . . .ndef when_handler when name , etc lbkt ( decl , etc )rbkt : body .or when name , etc ( * ) : body . . .ndef others_handler others lbkt ( idn : type_spec ) rbkt : body . . .ndef expression .nr prec_stop percent_stop+prec_width .nr curprec 6 primary .or ( expression ) .or ~ expressionprec() (precedence) .or - expressionprec() .or expression ** expressionnprec() .or expression // expressionnprec() .or expression / expressionprec() .or expression * expressionprec() .or expression || expressionnprec() .or expression + expressionprec() .or expression - expressionprec() .or expression < expressionnprec() .or expression <= expressionprec() .or expression = expressionprec() .or expression >= expressionprec() .or expression > expressionprec() .or expression ~< expressionprec() .or expression ~<= expressionprec() .or expression ~= expressionprec() .or expression ~>= expressionprec() .or expression ~> expressionprec() .or expression & expressionnprec() .or expression cand expressionprec() .or expression | expressionnprec() .or expression cor expressionprec() . . .ndef primary nil .or true .or false .or int_literal .or real_literal .or char_literal .or string_literal .or idn .or idn [ constant , etc ] .or primary . name .or primary [ expression ] .or invocation .or type_spec $ { field , etc } .or type_spec $ [ lbkt expression : rbkt lbkt expression , etc rbkt ] .or type_spec $ name lbkt [ constant , etc ] rbkt .or force [ type_spec ] .or up ( expression ) .or down ( expression ) . . .ndef invocation primary ( lbkt expression , etc rbkt ) . . .ndef field name , etc : expression . . .ndef .para 2Reserved word*: one of the identifiers appearing in bold face in the syntax. Upper and lower case letters are not distinguished in reserved words. .para 2Name*, 2idn*: a sequence of letters, digits, and underscores that begins with a letter or underscore, and that is not a reserved word. Upper and lower case letters are not distinguished in names and idns. .para 2Int_literal*: a sequence of one or more decimal digits. .para 2Real_literal*: a mantissa with an (optional) exponent. A mantissa is either a sequence of one or more decimal digits, or two sequences (one of which may be empty) joined by a period. The mantissa must contain at least one digit. An exponent is 'E' or 'e', optionally followed by '+' or '-', followed by one or more decimal digits. An exponent is required if the mantissa does not contain a period. .para 2Char_literal*: either a printing ASCII character (octal 40 thru octal 176), other than single quote or backslash, enclosed in single quotes, or one of the following escape characters enclosed in single quotes: .show escape sequence s(1)character .sp .5 \'t(1)' s(2)(single quote) \"t(1)"t(2)(double quote) \\t(1)\t(2)(backslash) \nt(1)NLt(2)(newline) \tt(1)HTt(2)(horizontal tab) \pt(1)FFt(2)(newpage) \bt(1)BSt(2)(backspace) \rt(1)CRt(2)(carriage return) \vt(1)VTt(2)(vertical tab) \***t(1)specified by octal value (* is an octal digit) .eshow The escape sequences may be written using upper case letters. .para 2String_literal*: a sequence of zero or more character representations, enclosed in double quotes. A character representation is either a printing ASCII character other than double quote or backslash, or one of the escape sequences listed above. .para 2Comment*: a sequence of characters that begins with a percent sign, ends with a newline character, and contains only printing ASCII characters and horizontal tabs in between. .para 2Separator*: a blank character (space, vertical tab, horizontal tab, carriage return, newline, form feed) or a comment. Zero or more separators may appear between any two tokens, except that at least one separator is required between any two adjacent non-self-terminating tokens: reserved words, identifiers, integer literals, and real literals. .eq or temp_or .eq def temp_def