Dedicated to my father Mikhail Tereshkov, who instilled in me a taste for engineering
XD Pascal is a small embeddable self-hosting compiler for a Pascal language dialect. Any comments, suggestions, or bug reports are appreciated. Feel free to contact the author on GitHub or by e-mail VTereshkov@mail.ru. Enjoy.
- Go-style methods and interfaces
- Native x86 code generation (32 bit Windows executables)
- Support for both console and GUI applications
- No external assembler or linker needed
- Floating-point arithmetic using the x87 FPU
- Integration with the Raylib game development library
- Integration with Geany IDE
- Compiler source for Delphi 6/7, Free Pascal and XD Pascal itself (Delphi 2009+ migration is straightforward)
Type in the command prompt:
xdpw <file.pas>
The source file should be specified with its extension (.pas).
XD Pascal is similar to Delphi 6/7 and Free Pascal with the following changes:
- The compiler is self-hosting
- The compiler is extremely compact (~10000 lines) and can be easily embedded into larger systems
- Go-style methods and interfaces are supported
- Strings are null-terminated arrays of characters (C style), but indexed from 1 for Pascal compatibility
- The
Text
type is equivalent tofile
. It can be used for both text and untyped files - Method calls and procedural variable calls require parentheses even for empty parameter lists
- No classical (C++/Delphi style) object-oriented programming
- No visual components
- Units cannot be compiled separately
- Only peephole optimizations
Extended
is equivalent toDouble
- No
High
andLow
functions for open arrays. Open array length should be explicitly passed to a subroutine - Statement labels cannot be numerical
ProgramOrUnit = [("program" | "unit") Ident ";"]
["interface"] [UsesClause] Block "." .
UsesClause = "uses" Ident {"," Ident} ";" .
Block = { Declarations } (CompoundStatement | "end") .
Declarations = DeclarationSection ["implementation" DeclarationSection] .
DeclarationSection = LabelDeclarations |
ConstDeclarations |
TypeDeclarations |
VarDeclarations |
ProcFuncDeclarations .
Initializer = ConstExpression |
StringLiteral |
"(" Initializer {"," Initializer} ")" |
"(" Ident ":" Initializer {";" Ident ":" Initializer} ")" |
SetConstructor .
LabelDeclarations = "label" Ident {"," Ident} ";"
ConstDeclarations = (UntypedConstDeclaration | TypedConstDeclaration)
{";" (UntypedConstDeclaration | TypedConstDeclaration)} .
UntypedConstDeclaration = "const" Ident "=" ConstExpression .
TypedConstDeclaration = "const" Ident ":" Type "=" Initializer .
TypeDeclarations = "type" Ident "=" Type ";" {Ident "=" Type ";"} .
VarDeclarations = "var" IdentList ":" Type ["=" Initializer] ";"
{IdentList ":" Type ["=" Initializer] ";"} .
ProcFuncDeclarations = ("procedure" | "function") Ident
[Receiver] [FormalParams] [":" TypeIdent]
[CallModifier] ";" [(Directive | Block) ";"] .
Receiver = "for" Ident ":" TypeIdent .
CallModifier = "stdcall" | "cdecl" .
Directive = "forward" | "external" ConstExpression .
ActualParams = "(" [ (Expression | Designator) |
{"," (Expression | Designator)} ] ")" .
FormalParams = "(" FormalParamList {";" FormalParamList} ")" .
FormalParamList = ["const" | "var"] IdentList [":" ["array" "of"] TypeIdent]
["=" ConstExpression] .
IdentList = Ident {"," Ident} .
Type = "(" Ident {"," Ident} ")" |
"^" TypeIdent |
["packed"] "array" "[" Type {"," Type} "]" "of" Type |
["packed"] "record" Fields "end" |
["packed"] "interface" FixedFields "end" |
["packed"] "set" "of" Type |
["packed"] "string" [ "[" ConstExpression "]" ] |
["packed"] "file" ["of" Type] |
ConstExpression ".." ConstExpression |
("procedure" | "function") [FormalParams] [":" TypeIdent] [CallModifier] |
Ident .
Fields = FixedFields
["case" [Ident ":"] Type "of"
ConstExpression {"," ConstExpression} ":" "(" Fields ")"
{";" ConstExpression {"," ConstExpression} ":" "(" Fields ")"}] [";"] .
FixedFields = IdentList ":" Type {";" IdentList ":" Type} .
TypeIdent = "string" | "file" | Ident .
Designator = BasicDesignator {Selector} .
BasicDesignator = Ident |
Ident [ActualParams] |
Ident "(" Expression ")" .
Selector = "^" |
"[" Expression {"," Expression} "]" |
"." Ident |
"(" ActualParams ")".
Statement = [Label ":"] [ (Designator | Ident) ":=" Expression |
(Designator | Ident) [ActualParams] {Selector} |
CompoundStatement |
IfStatement |
CaseStatement |
WhileStatement |
RepeatStatement |
ForStatement |
GotoStatement |
WithStatement ] .
Label = Ident .
StatementList = Statement {";" Statement} .
CompoundStatement = "begin" StatementList "end" .
IfStatement = "if" Expression "then" Statement ["else" Statement] .
CaseStatement = "case" Expression "of" CaseElement {";" CaseElement}
[";"] ["else" StatementList] [";"] "end" .
WhileStatement = "while" Expression "do" Statement .
RepeatStatement = "repeat" StatementList "until" Expression .
ForStatement = "for" Ident ":=" Expression ("to" | "downto") Expression "do" Statement.
GotoStatement = "goto" Label .
WithStatement = "with" Designator {"," Designator} "do" Statement .
CaseElement = CaseLabel {"," CaseLabel} ":" Statement .
CaseLabel = ConstExpression [".." ConstExpression] .
ConstExpression = Expression .
Expression = SimpleExpression [("="|"<>"|"<"|"<="|">"|">="|"in") SimpleExpression] .
SimpleExpression = ["+"|"-"] Term {("+"|"-"|"or"|"xor") Term}.
Term = Factor {("*"|"/"|"div"|"mod"|"shl"|"shr"|"and") Factor}.
Factor = (Designator | Ident) [ActualParams] {Selector} |
Designator |
"@" Designator |
Number |
CharLiteral |
StringLiteral |
"(" Expression ")" |
"not" Factor |
SetConstructor |
"nil" |
Ident "(" Expression ")" {Selector} .
SetConstructor = "[" [Expression [".." Expression]
{"," Expression [".." Expression]}] "]" .
Ident = (Letter | "_") {Letter | "_" | Digit}.
Number = "$" HexDigit {HexDigit} |
Digit {Digit} ["." {Digit}] ["e" ["+" | "-"] Digit {Digit}] .
CharLiteral = "'" (Character | "'" "'") "'" |
"#" Number .
StringLiteral = "'" {Character | "'" "'"} "'".
The compiler is based on a recursive descent parser. It directly builds a Windows PE executable without using any external assembler or linker.
$APPTYPE
- Set application type. Examples:{$APPTYPE GUI}
,{$APPTYPE CONSOLE}
$UNITPATH
- Set additional unit search path. Example:{$UNITPATH ..\units\}
Some simple peephole optimizations are performed:
- Push/pop elimination
- FPU push/pop elimination
- Local variable loading optimizations
- Array element access optimizations
- Record field access optimizations
- Assignment optimizations
- Comparison optimizations
- Condition testing optimizations
The following identifiers are implemented as part of the compiler. Their names are not reserved words and can be locally redefined by the user.
procedure Inc(var x: Integer);
procedure Dec(var x: Integer);
procedure Read([var F: file;] var x1 {; var xi});
procedure Write([var F: file;] x1[:w[:d]] {; xi[:w[:d]]});
procedure ReadLn([var F: file;] var x1 {; var xi});
procedure WriteLn([var F: file;] x1[:w[:d]] {; xi[:w[:d]]});
procedure New(var P: Pointer);
procedure Dispose(var P: Pointer);
procedure Break;
procedure Continue;
procedure Exit;
procedure Halt[(const error: Integer)];
function SizeOf(var x | T): Integer;
function Ord(x: T): Integer;
function Chr(x: Integer): Char;
function Low(var x: T | T): T;
function High(var x: T | T): T;
function Pred(x: T): T;
function Succ(x: T): T;
function Round(x: Real): Integer;
function Abs(x: T): T;
function Sqr(x: T): T;
function Sin(x: Real): Real;
function Cos(x: Real): Real;
function Arctan(x: Real): Real;
function Exp(x: Real): Real;
function Ln(x: Real): Real;
function SqRt(x: Real): Real;
function Timer: Integer;
procedure GetMem(var P: Pointer; Size: Integer);
procedure FreeMem(var P: Pointer);
procedure Randomize;
function Random: Real;
procedure Assign(var F: file; const Name: string);
procedure Rewrite(var F: file[; BlockSize: Integer]);
procedure Reset(var F: file[; BlockSize: Integer]);
procedure Close(var F: file);
procedure BlockRead(var F: file; var Buf; Len: Integer; var LenRead: Integer);
procedure BlockWrite(var F: file; var Buf; Len: Integer);
procedure Seek(var F: file; Pos: Integer);
function FileSize(var F: file): Integer;
function FilePos(var F: file): Integer;
function EOF(var F: file): Boolean;
function IOResult: Integer;
function Length(const s: string): Integer;
procedure Move(var Source; var Dest; Count: Integer);
function Copy(const S: string; Index, Count: Integer): string;
procedure FillChar(var Data; Count: Integer; Value: Char);
function ParamCount: Integer;
function ParamStr(Index: Integer): string;
procedure Val(const s: string; var Number: Real; var Code: Integer);
procedure Str(Number: Real; var s: string[; DecPlaces: Integer]);
procedure IVal(const s: string; var Number: Integer; var Code: Integer);
procedure IStr(Number: Integer; var s: string);
function UpCase(ch: Char): Char;
function IntToStr(n: Integer): string;
function StrToInt(const s: string): Integer;
function FloatToStr(x: Real): string;
function FloatToStrF(x: Real; Format: TFloatFormat; Precision, Digits: Integer): string;
function StrToFloat(const s: string): Real;
function StrToPChar(const s: string): PChar;
function PCharToStr(p: PChar): string;
function StrToPWideChar(const s: string): PWideChar;
function PWideCharToStr(p: PWideChar): string;
factor.pas
- Integer factorization demolineq.pas
- Linear equation solver. Usesgauss.pas
unit. Requireseq.txt
,eqerr.txt
, or similar data filelife.pas
- The Game of Lifesort.pas
- Array sorting demofft.pas
- Fast Fourier Transform demoinserr.pas
- Inertial navigation system error estimation demo. Useskalman.pas
unitlist.pas
- Linked list operations demomap.pas
- Heterogenous list operations and Map function demo. Demonstrates XD Pascal methods and interfacesgui.pas
- GUI application demo. Useswindows.pas
unitraytracer.pas
- Raytracer demo. Demonstrates XD Pascal methods and interfaces. Equivalent toraytracer.go
Windows Defender antivirus is known to give false positive results on some programs compiled with XD Pascal.