Component Pascal

Component Pascal is a programming language in the tradition of Niklaus Wirth's Pascal, Modula-2, Oberon and Oberon-2. It bears the name of the Pascal programming language but is incompatible with it. Instead, it is a minor variant and refinement of Oberon-2, designed and supported by a small ETH Zürich spin-off company called Oberon microsystems. Their IDE (Integrated Development Environment) is called BlackBox Component Builder. At the time the first version was released (1994 as Oberon/F) it presented a novel approach to graphical user interface (GUI) construction based on editable forms, where fields and command buttons are linked to exported variables and executable procedures. This approach bears some similarity to the code-behind way used in Microsoft's .NET 3.0 to access code in XAML.

An Open Source implementation exists for the .NET and Java Virtual Machine platforms, from the Gardens Point team around John Gough at Queensland University of Technology in Australia.

On June 23, 2004 Oberon Microsystems announced that the BlackBox Component Builder was made available as a free download and that an open source version was planned. The beta open source version was initially released in December, 2004 and updated to a final v1.5 release in December, 2005. It includes the complete source code of the IDE, compiler, debugger, source analyser, profiler and interfacing libraries and can also be downloaded from their website.

BlackBox Component Pascal uses the extensions .odc (= Oberon document) for document files, such as source files for example, and .osf (= Oberon symbol file) for symbol files while Gardens Point Component Pascal uses .cp for source and .cps for symbol files. BlackBox Component Pascal has its own executable and loadable object format .ocf (= Oberon code file); it includes a runtime linking loader for this format.

Syntax

The full syntax for CP, as given by the Language Report, is shown below. Note that in the extended Backus–Naur form only 34 grammatical productions are required, just one more than for Oberon-2, although it is a rather more advanced language.

Module = MODULE ident ";" [ImportList] DeclSeq 
           [BEGIN StatementSeq] 
           [CLOSE StatementSeq] 
         END ident ".".

ImportList = IMPORT [ident ":="] ident {"," [ident ":="] ident} ";".

DeclSeq = { CONST {ConstDecl ";" } 
          | TYPE {TypeDecl ";"} 
          | VAR {VarDecl ";"}} 
          { ProcDecl ";" | ForwardDecl ";"}.

ConstDecl = IdentDef "=" ConstExpr.

TypeDecl = IdentDef "=" Type.

VarDecl = IdentList ":" Type.

ProcDecl = PROCEDURE [Receiver] IdentDef [FormalPars] MethAttributes 
           [";" DeclSeq [BEGIN StatementSeq] 
           END ident].

MethAttributes = ["," NEW] ["," (ABSTRACT | EMPTY | EXTENSIBLE)].

ForwardDecl = PROCEDURE " ^ " [Receiver] IdentDef [FormalPars] MethAttributes.

FormalPars = "(" [FPSection {";" FPSection}] ")" [":" Type].

FPSection = [VAR | IN | OUT] ident {"," ident} ":" Type.

Receiver = "(" [VAR | IN] ident ":" ident ")".

Type = Qualident
    | ARRAY [ConstExpr {"," ConstExpr}] OF Type
    | [ABSTRACT | EXTENSIBLE | LIMITED] 
      RECORD ["("Qualident")"] FieldList {";" FieldList} END
    | POINTER TO Type
    | PROCEDURE [FormalPars].

FieldList = [IdentList ":" Type].

StatementSeq = Statement {";" Statement}.

Statement = [ Designator ":=" Expr
    | Designator ["(" [ExprList] ")"]
    | IF Expr THEN StatementSeq
        {ELSIF Expr THEN StatementSeq}
        [ELSE StatementSeq] END
    | CASE Expr OF Case {"|" Case}
        [ELSE StatementSeq] END
    | WHILE Expr DO StatementSeq END
    | REPEAT StatementSeq UNTIL Expr
    | FOR ident ":=" Expr TO Expr [BY ConstExpr] DO StatementSeq END
    | LOOP StatementSeq END
    | WITH [ Guard DO StatementSeq ] 
       {"|" [ Guard DO StatementSeq ] } 
       [ELSE StatementSeq] 
      END
    | EXIT
    | RETURN [Expr]
    ].

Case = [CaseLabels {"," CaseLabels} ":" StatementSeq].

CaseLabels = ConstExpr [".." ConstExpr].

Guard = Qualident ":" Qualident.

ConstExpr = Expr.

Expr = SimpleExpr [Relation SimpleExpr].

SimpleExpr = ["+" | "-"] Term {AddOp Term}.

Term = Factor {MulOp Factor}.

Factor = Designator | number | character | string | NIL | Set | "(" Expr ")" | " ~ " Factor.

Set = "{" [Element {"," Element}] "}".

Element = Expr [".." Expr].

Relation = "=" | "#" | "<" | "<=" | ">" | ">=" | IN | IS.

AddOp = "+" | "-" | OR.

MulOp = " * " | "/" | DIV | MOD | "&".

Designator = Qualident {"." ident 
             | "[" ExprList "]" 
             | " ^ " 
             | "(" Qualident ")" 
             | "(" [ExprList] ")"} [ "$" ].

ExprList = Expr {"," Expr}.

IdentList = IdentDef {"," IdentDef}.

Qualident = [ident "."] ident.

IdentDef = ident [" * " | "-"].

External links

• Oberon microsystems
• Component Pascal Language Report
• What's new in Component Pascal?
• More Information / Download the BlackBox Component Builder
• Open Source License for the framework
• Gardens Point Component Pascal
• Component Pascal Collection with many useful sources
• Component Pascal Resources
• Component Pascal at the Open Directory Project

Evolution of Oberon and Oberon-2

• "From Modula-2 to Oberon" Wirth (1988)
• "The Programming Language Oberon" Wirth (1988)
• "Differences between Oberon and Oberon-2" Mössenböck and Wirth (1991)
• "The Programming Language Oberon-2" H. Mössenböck, N. Wirth, Institut für Computersysteme, ETH Zürich, January 1992
• "What's New in Component Pascal" (Changes from Oberon-2 to CP), Pfister (2001)