Appendix C
Compatibility with PL/I Standards
This appendix describes the differences between Endless PL/I for POSIX Systems and the various PL/I language standards that are currently in force.
Endless PL/I for POSIX Systems is a strict superset of the ANSI X3.74-1981 PL/I General Purpose Subset and provides most of the features of the new ANSI X3.74-1987 PL/I General Purpose Subset and many of the features of the ANSI X3.53-1976 (full) PL/I language standard. Endless PL/I for POSIX Systems provides the SAA tm Common Programming Interface of IBM, compatibility with Digital (VAX PL/I, DEC PL/I) and other dialects of PL/I (such as LIANT and Stratus PL/I).
C.1. Relation to the 1981 PL/I General-Purpose Subset
The 1981 PL/I General-Purpose Subset (ANSI X3.74-1981) was designed to be useful in scientific, commercial, and systems programming, especially on small and medium-size computer systems. Among the primary goals of the design of the subset were the following:
To include features that were easy to learn and to use and to exclude features that were difficult to learn or prone to error
To provide a subset that would be easily portable from one computer system to another
To exclude features that were not often used and whose implementation greatly increased the complexity of the run-time support required by the compiler
The essential elements of the subset are described below. These descriptions are extracted from the ANSI X3.74-1981 standard.
C.1.1. Program Structure
The General-Purpose Subset includes a complete character set, with comments, identifiers, decimal arithmetic constants, and simple string constants.
Begin blocks and DO-groups are included in the subset. Each block or group in the program must be terminated with an END statement.
C.1.2. Program Control
The following program control statements are included in the subset: CALL, RETURN, IF, DO, GOTO, null, STOP, ON, REVERT, and SIGNAL.
The DO statement options supported are TO, BY, WHILE, and REPEAT.
An IF statement can contain unlabeled THEN and ELSE clauses.
An ON statement can specify a single condition. The condition names supported are ERROR, ENDFILE, ENDPAGE, FIXEDOVERFLOW, KEY, OVERFLOW, UNDEFINEDFILE, UNDERFLOW, and ZERODIVIDE.
C.1.3. Storage Control
The subset includes the assignment statement and the assignment of array and structure variables whose dimensions and data types match. The subset also permits aggregate promotion, that is, the assignment of a scalar expression to every element or member of an aggregate variable.
In the subset, only static variables can be initialized.
The ALLOCATE statement with the SET option and the FREE statement are included in the subset.
C.1.4. Input/Output
The I/O statements are:
OPEN and CLOSE
READ, WRITE, DELETE, and REWRITE for record I/O
GET and PUT, with FILE, STRING, EDIT, LIST, PAGE, SKIP, and LINE options for stream I/O
The file attributes, specified in DECLARE or OPEN, are DIRECT, ENVIRONMENT, INPUT, KEYED, OUTPUT, PRINT, RECORD, SEQUENTIAL, STREAM, and UPDATE.
The FORMAT statement is included. The format items are E, F, P, A, B, X, R, PAGE, SKIP, COLUMN, TAB, and LINE.
C.1.5. Attributes and Pictures
The DECLARE statement is included in the subset. All names must be declared, either by means of a DECLARE statement or by means of a label prefix.
The attributes supported are as follows: ALIGNED, AUTOMATIC, BASED, BINARY, BIT, BUILTIN, CHARACTER, DECIMAL, DEFINED, DIRECT, ENTRY, ENVIRONMENT, EXTERNAL, FILE, FIXED, FLOAT, INITIAL, INPUT, INTERNAL, KEYED, LABEL, OPTIONS, OUTPUT, PICTURE, POINTER, PRINT, RECORD, RETURNS, SEQUENTIAL, STATIC, STREAM, UPDATE, VARIABLE, and VARYING.
The picture characters included are CR, DB, S, V, Z, 9,-, +, $, and *. The picture insertion characters (. , / B) are also included.
C.1.6. Built-In Functions and Pseudovariables
The built-in functions in the subset are as follows: ABS, ACOS, ADDR, ASIN, ATAN, ATAND, ATANH, BINARY, BIT, BOOL, CEIL, CHARACTER, COLLATE, COPY, COS, COSD, COSH, DATE, DECIMAL, DIMENSION, DIVIDE, EXP, FIXED, FLOAT, FLOOR, HBOUND, INDEX, LBOUND, LENGTH, LINENO, LOG, LOG2, LOG10, MAX, MIN, MOD, NULL, ONCODE, ONFILE, ONKEY, PAGENO, ROUND, SIGN, SIN, SIND, SINH, SQRT, STRING, SUBSTR, TAN, TAND, TANH, TIME, TRANSLATE, TRUNC, UNSPEC, and VERIFY.
The pseudovariables are PAGENO, STRING, SUBSTR, and UNSPEC.
C.1.7. Expressions
The subset supports all infix and prefix operators, the locator qualifier, parenthesized expressions, subscripts, and function references. Implicit conversion from one data type to another is restricted to those contexts in which the conversion is likely to produce the desired results.
C.2. 198x PL/I General-Purpose Subset Features Supported
The 198x PL/I General-Purpose Subset (ANSI X3.74-198x) was designed to extend the previous subset standard on the basis of experience with subset implementations and the desire for more capabilities in subset-conforming implementations.
The following sections describe features in this standard that have been implemented to date in Endless PL/I for POSIX Systems.
C.2.1. Lexical Constructs
The character pair /* is permitted within comments.
Both uppercase and lowercase characters are permitted in source programs.
No space is required after the P for picture constants.
C.2.2. Program Control
RETURNS(CHAR(*)) is supported.
The statements following THEN and ELSE can be labeled.
The NONRECURSIVE procedure option is supported.
The SELECT and LEAVE statements are supported.
The UNTIL clause for DO groups and clauses is supported.
The AREA, CONDITION, CONVERSION, FINISH, and STORAGE conditions are supported.
Multiple conditions can be specified for ON and REVERT.
The SYSTEM option of the ON statement is supported.
C.2.3. Storage Control
The IN option can be used for the ALLOCATE and FREE statements, and language controlled allocation in areas is supported.
The SET option is optional for ALLOCATE if the based variable being allocated was declared with a base pointer.
The ALLOCATE and FREE statements can specify a comma list of items.
String assignment can have the source and target overlapped.
C.2.4. Input/Output
Expressions can be used in GET and PUT FORMAT lists.
You can use, as the source or target of a file I/O statement, a function reference that performs I/O on the same file and then returns to the original statement.
The OPEN and CLOSE statements can contain a list of file specifications.
The FROM option of the REWRITE statement can be omitted.
C.2.5. Attributes and Pictures
The INITIAL attribute is allowed with AUTOMATIC storage. The initial items can contain asterisks to denote uninitialized values. The initial values can be expressions. The NULL built-in function can be used in both STATIC and AUTOMATIC INITIAL attributes. The initial iteration factor can be an asterisk.
Restricted expressions can be used for static extents, parameter extents, and returns descriptor extents.
The AREA and OFFSET data types are supported.
The REFER attribute can be used at the end of a structure.
The DIMENSION, PARAMETER, and NONVARYING keywords can be specified.
The UNALIGNED attribute can be specified, but only for BIT and CHARACTER variables.
SYSIN and SYSPRINT can be contextually declared as files.
The CONDITION attribute is supported.
The UNION attribute is supported.
C.2.6. Built-In Functions and Pseudovariables
The following built-in functions are supported: ADD, EMPTY, EVERY, HIGH, LOW, MULTIPLY, ONSOURCE, POINTER, REVERSE, SOME, and SUBTRACT.
The ONSOURCE pseudovariable is supported.
The INDEX and VERIFY built-in functions have an optional starting position parameter.
The UNSPEC built-in function and pseudovariable can be used on aggregates.
C.2.7. Expressions
The operators AND THEN (short-circuiting AND, specified as &:, and OR ELSE (short- circuiting OR, specified as |:, are supported.
EXCLUSIVE OR (infix or dyadic ^) is supported.
C.3. Full PL/I Features Supported
The items discussed in this section are features that are explicitly excluded from both the old subset standard (ANSI X3.74-1981) and the new subset standard (ANSI X3.74-198x) but that have been implemented in Endless PL/I for POSIX Systems. These features all exist in full PL/I.
C.3.1. Program Structure
The STRINGRANGE and SUBSCRIPTRANGE conditions are supported.
Replication factors for string constants are supported.
A comma list can be specified on the left-hand side of an assignment statement.
C.3.2. Program Control
The ENTRY statement is supported.
C.3.3. Storage Control
CONTROLLED storage is supported.
C.3.4. Attributes and Pictures
The CONTROLLED, LIKE, MEMBER, POSITION, PRECISION, REFER, and STRUCTURE attributes are supported. (The REFER attribute is restricted to BASED and CONTROLLED variables.)
The picture characters Y, T, I, R, F, K, and E are supported, and pictures can include iteration factors.
C.3.5. Built-In Functions and Pseudovariables
The POINTER built-in function is not restricted to ADDR.
The ALLOCATION and ONCHAR built-in functions are supported.
The ONCHAR pseudovariable is supported.
C.3.6. Expressions
The expression in a WHILE or UNTIL clause or in an IF statement can be a bit string of any length. When evaluated, the expression results in a true value if any bit of the string expression is a 1 and in a false value if all bits in the string expression are 0s.
The control variable and the expressions in the TO, BY, and REPEAT options of the DO statement are not restricted to integers and pointers.
C.4. Nonstandard Features from Other Implementations
The features discussed in this section are not described in any ANSI PL/I standard. They are, however, provided by some other implementations.
C.4.1. Preprocessor
Endless PL/I for POSIX Systems supports an embedded lexical preprocessor for compilation control. This feature is
included for compatibility with PL/I for OpenVMS. Endless Software Solutions suggests you use the preprocessor only if you
require this compatibility. Therefore, it is turned on by default for the -D dec variant and off, by
default, for the -D ansi and -D ibm variants.
The following preprocessor statements are included: %ACTIVATE, %DEACTIVATE, %DECLARE, %DO, %END, %ERROR, %FATAL, %GOTO, %INFORM, %IF, %LIST (ignored), %NOLIST (ignored), %PAGE, %PROCEDURE, %REPLACE, %RETURN, %SBTTL, %TITLE, and %WARN.
An %IF statement can contain unlabeled %THEN and %ELSE clauses.
The following preprocessor built-in functions are included: ABS, BYTE, COPY, DATE, DATETIME, DECODE, ENCODE, ERROR, INDEX, INFORM, LENGTH, LINE, MAX, MIN, MOD, RANK, REVERSE,SEARCH, SIGN, SUBSTR, TIME, TRANSLATE, TRIM, VARIANT, VERIFY, and WARN.
C.4.2. Program Control
Endless PL/I for POSIX Systems, IBM dialect, supports condition prefixes and the following conditions:
ATTENTION, CHECK, NAME, RECORD, SIZE, STRINGSIZE, TRANSMIT
C.4.3. IBM Dialect I/O Features and Other IBM Dialect Features
Endless PL/I for POSIX Systems, IBM dialect, supports several features to facilitate IBM file handling. See Appendix B, Dialect Differences for more information on these and other IBM dialect features.
C.4.4. Built-In Functions
The following nonstandard built-in functions are included: BYTE, BYTESIZE, DATETIME, DECODE, ENCODE, INT, MAXLENGTH, POSINT, RANK, SEARCH, SIZE, and TRIM.
C.4.5. LIKE Extension
Endless PL/I for POSIX Systems lets you use the LIKE attribute on a structure already containing LIKE.
C.4.6. Declarations
Variables can be declared outside procedures.
The extensions in the following sections are enhancements for PL/I programs executing on POSIX systems. These extensions are provided for procedure calling, condition handling, compilation control, and miscellaneous purposes.
C.5.1. Procedure-Calling and Condition-Handling Extensions
The following extensions to PL/I were made to allow procedures to call procedures written in any other programming language that also supports the OpenVMS calling standard.
The ANY, VALUE, and REFERENCE attributes describe how data is to be passed to a called procedure.
The OPTIONAL attribute indicates that a parameter need not be specified in a call; the TRUNCATE attribute indicates the point at which an actual parameter list can be truncated.
The LIST attribute can be used for the parameter descriptor in an external entry declaration to denote that a list of parameters may be specified.
The VARIABLE option for the ENTRY attribute permits a PL/I procedure to call a non-PL/I procedure with an argument list of variable length. It also permits a procedure to omit arguments in an argument list.
The following attributes provide storage classes for PL/I variables. These attributes permit PL/I programs interact with other procedures that use these storage classes.
The GLOBALDEF and GLOBALREF attributes let you define and access external global variables and optionally place all external global definitions in the same program section.
The READONLY attribute can be applied to a static computational variable whose value does not change.
The VALUE attribute defines a variable that is, in effect, a constant whose value is supplied by the linker. The value attribute can also be used to allow a procedure to receive constants passed by immediate value.
The following extensions to condition handling provide compatibility with condition handling in PL/I for OpenVMS product:
The ANYCONDITION condition name can be used in an ON-unit to handle any condition that is signaled that does not explicitly have an ON-unit of its own.
The VAXCONDITION condition name can be used in ON, SIGNAL, and REVERT statements to process conditions specific to OpenVMS systems.
The RESIGNAL built-in subroutine permits an ON-unit to keep a signal active.
C.5.2. Miscellaneous Extensions
The following built-in functions are supported: BYTE, DECODE, ENCODE, INT, POSINT, RANK, and SIZE.
C.6. Implementation-Defined Values and Features
The following values and features are implementation-defined:
Endless PL/I for POSIX Systems supports the full 256-character DEC Multinational Character Set (a superset of ASCII) for CHARACTER data (including character string constants in PL/I source programs). All identifiers in a source program are restricted to the ASCII character set.
The default precisions for arithmetic data are listed in Chapter 3, Data Types .
The maximum record size for SEQUENTIAL files is 32767 bytes minus the length of any fixed-length control area.
The maximum key size is 255 bytes for character keys.
The default value for the LINESIZE option is as follows:
If the output is to a physical record-oriented device, such as a line printer or terminal, the line size is the width of the device.
If the output is to a print file, the line size is 132.
If the output is to a nonrecord device (magnetic tape), the line size is 510.
The values for TAB positions are columns beginning with column 1 and every eight columns thereafter.
The maximum length allowed for a file title is 128 characters.
The maximum number of digits in editing fixed-point data is 34.
The maximum numbers of digits for each combination of base and scale are listed in Chapter 3, Data Types .
The maximum length of CHARACTER, CHARACTER VARYING, and BIT strings is 32767.
The default precision for integer values is listed in Chapter 3, Data Types .
The maximum number of arguments that can be passed to an entry point is 253.
The second parameter of the F format item (the optional parameter specifying the number of fractional digits in the stream representation) must have a value less than or equal to 31.