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Sample Translation
Source code
void Foo() { int a, b, max; read a; read b; if (a > b) max = a; else max = b; write max; }
Object code
1: ENTER 3
4: READ
5: STO 0
8: READ
9: STO 1
12: LOAD 0
15: LOAD 1
18: GTR
19: FJMP 31
22: LOAD 0
25: STO 2
28: JMP 37
31: LOAD 1
34: STO 2
37: LOAD 2
40: WRITE
41: LEAVE
42: RET
Scanner Specification
COMPILER Taste
CHARACTERS letter = 'A'..'Z' + 'a'..'z'. digit = '0'..'9'.
TOKENS ident = letter {letter | digit}. number = digit {digit}.
COMMENTS FROM "/" TO "/" NESTED COMMENTS FROM "//" TO '\r' '\n'
IGNORE '\r' + '\n' + '\t'
PRODUCTIONS ... END Taste.
Code Generator Class
public class CodeGenerator { public int pc ; public int progStart ; public CodeGenerator () {...} public void Emit (int op) {...} public void Emit (int op, int val) {...} public void Patch (int adr, int val) {...} ... }
Parser Specification -- Declarations
PRODUCTIONS
Taste (. string name; .) = "program" Ident (. tab.OpenScope(); .) '{' { VarDecl } { ProcDecl } '}' (. tab.CloseScope(); .).
VarDecl (. string name; int type; .) = Type Ident (. tab.Insert(name, VAR, type); .) { ',' Ident (. tab.Insert(name, VAR, type); .) } ';'.
ProcDecl (. string name; Obj obj; int adr; .) = "void" Ident (. obj = tab.Insert(name, PROC, UNDEF); obj.adr = gen.pc; if (name == "Main") gen.progStart = gen.pc; tab.OpenScope(); .) '(' ')' '{' (. gen.Emit(ENTER, 0); adr = gen.pc - 2; .) { VarDecl | Stat } '}' (. gen.Emit(LEAVE); gen.Emit(RET); gen.Patch(adr, tab.topScope.adr); tab.CloseScope(); .).
Type = (. type = UNDEF; .) ( "int" (. type = INT; .) | "bool" (. type = BOOL; .) ).
public SymbolTable tab; public CodeGenerator gen;
Parser Specification -- Factor
Factor (. int n; Obj obj; string name; .) = (. type = UNDEF; .) ( Ident (. obj = tab.Find(name); type = obj.type; if (obj.kind == VAR) { if (obj.level == 0) gen.Emit(LOADG, obj.adr); else gen.Emit(LOAD, obj.adr); } else SemErr("variable expected"); .)
| number (. n = Convert.ToInt32(t.val); gen.Emit(CONST, n); type = INT; .)
| '-' Factor (. if (type != INT) { SemErr("integer type expected"); type = INT; } gen.Emit(NEG); .)
| "true" (. gen.Emit(CONST, 1); type = BOOL; .) | "false" (. gen.Emit(CONST, 0); type = BOOL; .) ).
Ident = ident (. name = t.val; .).
Parser Specification -- Statements
Stat (. int type; string name; Obj obj; int adr, adr2, loopstart; .) = Ident (. obj = tab.Find(name); .) ( '=' (. if (obj.kind != VAR) SemErr("can only assign to variables"); .) Expr ';' (. if (type != obj.type) SemErr("incompatible types"); if (obj.level == 0) gen.Emit(STOG, obj.adr); else gen.Emit(STO, obj.adr); .) | '(' ')' ';' (. if (obj.kind != PROC) SemErr("object is not a procedure"); gen.Emit(CALL, obj.adr); .) )
| "read" Ident ';' (. obj = tab.Find(name); if (obj.type != INT) SemErr("integer type expected"); gen.Emit(READ); if (obj.level == 0) gen.Emit(STOG, obj.adr); else gen.Emit(STO, obj.adr); .)
| "write" Expr ';' (. if (type != INT) SemErr("integer type expected"); gen.Emit(WRITE); .)
| '{' { Stat | VarDecl } '}'
Main Program of Taste
using System;
public class Taste {
public static void Main (string[] arg) { if (arg.Length > 0) { Scanner scanner = new Scanner(arg[0]); Parser parser = new Parser(scanner); parser.tab = new SymbolTable(parser); parser.gen = new CodeGenerator(); parser.Parse(); if (parser.errors.count == 0) parser.gen.Interpret("Taste.IN"); } else Console.WriteLine("-- No source file specified"); }
Building the whole thing
c:> coco Taste.atg c:> csc Taste.cs Scanner.cs Parser.cs SymbolTable.cs CodeGenerator.cs c:> Taste Sample.tas
Summary
- Coco/R generates a scanner and a recursive descent parser from an attributed grammar
- LL(1) conflicts can be handled with resolvers
Grammars for C# and Java are available in Coco/R format
- Coco/R is open source software (Gnu GPL)
http://ssw.jku.at/Coco/
- Coco/R has been used by us to build
- a white-box test tool for C#
- a profiler for C#
- a static program analyzer for C#
- a metrics tool for Java
- compilers for domain-specific languages
- a log file analyzer
- ...
- Many companies and projects use Coco/R
- SharpDevelop: a C# IDE www.icsharpcode.net
- Software Tomography: Static Analysis Tool www.software-tomography.com
- CSharp2Html: HTML viewer for C# sources www.charp2html.net
- currently 39000 hits for Coco/R in Google
