BNF Definition of the XPL Language

<program>		::= <statement list> EOF
<statement list>	::= <statement>
			 | <statement list> <statement>
<statement> 		::= <basic statement>
			 | <if statement>
<basic statement> 	::= <assignment> ;
			 | <group> ;
			 | <procedure definition> ;
			 | <return statement> ;
			 | <call statement> ;
			 | <go to statement> ;
			 | <declaration statement> ;
 | ;
			 | <label definition> <basic statement>
<if statement> 	::= <if clause> <statement> 
			 | <if clause> <true part> <statement>
			 | <label definition> <if statement>
<if clause>		::= IF <expression> THEN 
<true part>	 ::= <basic statement> ELSE
<group> ::= <group head> <ending>
<group head> ::= DO ;
 | DO <step definition> ;
 | DO <while clause> ;
 | DO <case selector> ;
 | <group head> <statement>
<step definition> ::= <variable> <replace> <expression> <iteration control>
<iteration control> ::= TO <expression>
 | TO <expression> BY <expression>
<while clause>	 ::= WHILE <expression>
<case selector> ::= CASE <expression>
<procedure definition> ::= <procedure head> <statement list> <ending>
<procedure head> ::= <procedure name> ;
 | <procedure name> <type> ;
 | <procedure name> <parameter list> ;
 | <procedure name> <parameter list> <type> ;
<procedure name> ::= <label definition> PROCEDURE
<parameter list> ::= <parameter head> <identifier> )
<parameter head> ::= (
 | <parameter head> <identifier> ,
<ending> ::= END
 | END <identifier>
 | <label definition> <ending>
<label definition> ::= <identifier> :
<return statement> ::= RETURN
 | RETURN <expression>
<call statement> ::= CALL <variable>
<go to statement> ::= <go to> <identifier>
<go to> ::= GO TO
 | GOTO
<declaration statement> ::= DECLARE <declaration element>
		 | <declaration statement> , <declaration element>
<declaration element> ::= <type declaration>
 | <identifier> LITERALLY <string>
<type declaration> ::= <identifier specification> <type>
 | <bound head> <number> ) <type>
 | <type declaration> <initial list>
<type> ::= FIXED
 | CHARACTER
 | LABEL
 | <bit head> <number> )
<bit head> ::= BIT (
<bound head> ::= <identifier specification> (
<identifier specification> ::= <identifier>
 | <identifier list> <identifier> )
<identifier list> ::= (
 | <identifier list> <identifier> ,
 
<initial list> ::= <initial head> <constant> )
<initial head> ::= INITIAL (
 | <initial head> <constant> ,
<assignment> ::= <variable> <replace> <expression>
 | <left part> <assignment>
<replace> ::= =
<left part> ::= <variable> ,
<expression> ::= <logical factor>
 | <expression> | <logical factor>
<logical factor> ::= <logical secondary>
 | <logical factor> & <logical secondary>
<logical secondary> ::= <logical primary>
 | ¬ <logical primary>
<logical primary> ::= <string expression>
 | <string expression> <relation> <string expression>
<relation> ::= =
 | <
 | >
 | ¬ =
 | ¬ <
 | ¬ >
 | < =
 		 | > =
<string expression> ::= <arithmetic expression>
			 | <string expression> ||  <arithmetic expression>
<arithmetic expression> ::= <term>
 | <arithmetic expression> + <term>
 | <arithmetic expression> - <term>
 | + <term>
 | - <term>
<term> ::= <primary>
 | <term> * <primary>
 | <term> / <primary>
 | <term> MOD <primary>
<primary> ::= <constant>
 | <variable>
 | ( <expression> )
<variable> ::= <identifier>
 | <subscript head> <expression> )
<subscript head> ::= <identifier> (
 | <subscript head> <expression> ,
<constant> ::= <string>
 | <number>

---

The following definitions are hardcoded into the lexical scanner:

<number>	 ::= <integer>
 | <bit string>
<integer> ::= <decimal digit>
 | <integer> <decimal digit>
<decimal digit> ::= 0|1|2|3|4|5|6|7|8|9
<bit string> ::= "<bit list>"
<bit list> ::= <hex integer>
		 | <bit group>
 | <bit list> <bit group>
<bit group> ::= (1)<binary integer>
 | (2)<quartal integer>
 | (3)<octal integer>
 | (4)<hex integer>
<binary integer> ::= <binary digit>
 | <binary integer> <binary digit>
<binary digit> ::= 0|1
<quartal integer> ::= <quartal digit>
 | <quartal integer> <quartal digit>
<quartal digit> ::= 0|1|2|3
<octal integer> ::= <octal digit>
 | <octal integer> <octal digit>
<octal digit> ::= 0|1|2|3|4|5|6|7
<hex integer> ::= <hex digit>
 | <hex integer> <hex digit>
<hex digit> ::= 0|1|2||3|4|5|6|7|8|9|A|B|C|D|E|F
<string> ::= '<characters>'
 | ''
<characters> ::= <character>
 | <characters> <character>
<character> ::= ''
 | {any EBCDIC character other than ' }
<identifier> ::= <id character>
 | <identifier> <id character>
 | <identifier> <decimal digit>
<id character> ::= <letter> | <break character>
<letter> ::= A|B|C ... |Z|a|b|c ... |z
<decimal digit> ::= 0|1| ... |9
<break character> ::= _ | @ | # | $
No identifier can exceed 256 characters. The following reserved words cannot be
used as identifiers:
 BIT DECLARE GOTO PROCEDURE
 BY ELSE IF RETURN
 CALL END INITIAL THEN
 CASE EOF LABEL TO
 CHARACTER FIXED LITERALLY WHILE
 DO GO MOD
<comment> ::= <opening bracket> <almost anything> <closing bracket>
<opening bracket> ::= /*
<closing bracket> ::= */
<almost anything> ::= {any string of valid characters which does not contain a <closing bracket>}
A $ within a comment specifies that the next <character> is a control character.
There are 256 control toggles corresponding to the 256 valid character codes. 
Each toggle can have a value true or false. 
When $<character> is encountered, the value of the corresponding toggle is complemented. 
Currently defined toggles are:

toggle
Description
initial
B
Interlist emitted byte codes in hex.
off
D
Print statistics and symbol table.
on
E
Interlist emitted assembly code.
off
L
List compiled program.
on
M
List program without auxiliary information.
off
N
Warn if procedure args¬=parameters.
off
S
Dump symbol table at end of each procedure.
off
T
Begin tracing.
 
U
Terminate tracing.
 
Z
Allow program to execute in spite of errors.
off
|
Set margin. Input scan will be terminated at column containing the |