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 | |
|