SYNTAX SUMMARY

This appendix defines the syntax of ALGOL entities in a notation known as Backus Normal Form (BNF). In this notation, entities are defined in terms of other entities in the following format:

This notation means that the entity <a> consists of the entity followed by entity <c>. A entity bracketed by < and > is defined further elsewhere in the syntax. Anything not appearing between < and > stands for itself.

For example

<a> ::= <d> #BEGIN#

If one entity can be defined by more than one sequence, the sequences are separated by vertical lines:

<a> ::= <c> | <d> #BEGIN#

In this example the entity <a> consists of either followed by entity <c>, or <d> followed by the characters #BEGIN#.

The entity being defined can also appear in the definition, in which case the definition is recursive. For example:

<a> ::= <c> | <d> #BEGIN# | <a> <e>

This definition means that <a> consists of either followed by entity <c>, or <d> followed by the characters #BEGIN#, followed in either case by any number (including none) of occurrences of <e>.

The representation of syntax in this appendix does not correspond precisely to the representation of syntax in the main text of the manual, but the ultimate syntax of an ALGOL program is the same in both cases.

<empty> ::=

<letter> ::= A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | Y | W | X | Y | Z

<digit> ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

<logical value> ::= #TRUE# | #FALSE#

<arithmetic operator> ::= + | - | * | / | // | ** | ^

<relational operator> ::= < | #le# | = | #ge# | > | ~=

<logical operator> ::= #EQUIV# | #IMPL# | #and# | #OR# | ~

<sequential operator> ::= #GO TO# | #IF# | #THEN# | #ELSE# | #FOR# | #DO#

<separator> ::= # | , | . | : | ; | := | #STEP# | #UNTIL# | #WHILE# | #COMMENT# | #CODE# | #ALGOL# | #FORTRAN# | #RJ#

<bracket> ::= ) | ( | ] | [ | #(# | #)# | #BEGIN# | #END#

CONSTITUENTS OF EXPRESSIONS

<subscripted variable> ::= <array identifier> [ <subscript list>]

< procedure identifier> ::= < identifier>

<parameter delimiter> ::= , | )<letter string>:(

EXPRESSIONS

<adding operator> ::= + | -

< multiplying operator> ::= * | / | //

<primary> ::= <unsigned number> | <variable> | <function designator> | (<arithmetic expression>)

<if clause> ::= #IF# <Boolean expression> #THEN#

<relational operator > ::= < | #le# | = | #ge# | > | ~=

<Boolean primary>::= <logical value> | <variable> | <function designator> | <relation> | (<Boolean expression>)

<simple Boolean> ::= <implication> | <simple Boolean> #equiv# <implication>

<switch designator> ::= <switch identifier>[<subscript expression>]

<simple designational> ::= <label> | <switeh designator> | (<designational expression>)

COMPOUND STATEMENTS AND BLOCKS

<block head> ::= #BEGIN# <declaration> | <block head >; < declaration >

<unlabeled compound> ::= #BEGIN# <compound tail>

STATEMENTS AND BASIC STATEMENTS

<left part> ::= <destination> :=

<parameter delimiter> ::= , | )<letter string>:(

<actual parameter part> ::= <empty> | (<actual parameter list>)

<for list element> ::= <arithmetic expression> | <arithmetic expression> #STEP# <arithmetic expression> #UNTIL# <arithmetic expression> | <arithmetic expression> #WHILE#< Boolean expression>

<for clause> ::= #FOR# <variable identifier> := <for list> #DO#

<if clause> ::= #IF# <Boolean expression> #THEN#

DECLARATIONS

<type> ::= #REAL# | #INTEGER# | #BOOLEAN#

<local or own> ::= <empty> | #OWN#

<array declarer> ::= < type> #ARRAY# | #ARRAY#

<switch declaration> ::= #SWITCH# <switch identifier> := <switch list>

<formal parameter part> ::= <empty> | (<formal parameter list>)

<value part> ::= #VALUE# <identifier list>; | <empty>

<separate specification part> ::= <empty> | <separate specifier><identifier list>; | <separate specification part> <separate specifier> <identifier list>;

<code> ::= #CODE# <code specifier> <code identifier> | #ALGOL#<code specifier><code identifier> | #FORTRAN#<code identifier>

<separate procedure declaration> ::= #PROCEDURE# <separate procedure heading>

<separate procedure body> | <type>#PROCEDURE# <separate procedure heading> <separate procedure body>

<specification part> ::= <empty> | <specifier> <identifier list>; | <specification part> <specifier> <identifier list>;

<procedure declaration>::= #PROCEDURE# <procedure heading> <procedure body> | <type> #PROCEDURE# <procedure heading> <procedure body>

I scanned, OCRed, and proofread the Backus-Naur form of Algol-60 from an old CDC Manual I had still lying around. Please do not blame me for any errors. Use at your own risk. I would like to add that the representation here is partially due to the awkward 6 bit character code CDC used. In general, what is written here as hash sign (#) is normally represented by a double quote ("). I replaced some characters in the printed version, where I have no idea what ASCII I should use by the appropriate keywords (e.g., right arrow by #IMPL# or the greater equal sign by #GE#).

Bernhard Treutwein - BdT(at)wildwein(dot)de