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PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Growing Languages with Metamorphic Syntax Macros
Claus Brabrand
Michael Schwartzbach
BRICS, University of Aarhus, Denmark
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Outline
• Introduction
• Metamorphisms
• vDSL
• Specificity parsing
• Related and future work
• Conclusion
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Lexical Macros
• MLEX: (TOKENS)n TOKENS, n 0
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Lexical Macros
• MLEX: (TOKENS)n TOKENS, n 0
#define square(X) X*X#define square(X) X*X
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Lexical Macros
• MLEX: (TOKENS)n TOKENS, n 0
#define square(X) X*X
square(y+1) y+1*y+1
#define square(X) X*X
square(y+1) y+1*y+1
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Lexical Macros
• MLEX: (TOKENS)n TOKENS, n 0
#define square(X) X*X
square(y+1) y+1*y+1
#define square(X) X*X
square(y+1) y+1*y+1
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Lexical Macros
• MLEX: (TOKENS)n TOKENS, n 0
#define square(X) X*X
square(y+1) y+1*y+1
#define square(X) X*X
square(y+1) y+1*y+1
#define square(X) (X)*(X)
square(y+1) (y+1)*(y+1)
#define square(X) (X)*(X)
square(y+1) (y+1)*(y+1)
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Lexical Macros
• MLEX: (TOKENS)n TOKENS, n 0
• Problem: Independent of syntax!• Unsafe: parse errors discovered at invocation-time
#define square(X) X*X
square(y+1) y+1*y+1
#define square(X) X*X
square(y+1) y+1*y+1
#define square(X) (X)*(X)
square(y+1) (y+1)*(y+1)
#define square(X) (X)*(X)
square(y+1) (y+1)*(y+1)
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Invocation Syntax
#define swap(X,Y) { int t=X; X=Y; Y=t; }#define swap(X,Y) { int t=X; X=Y; Y=t; }
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Invocation Syntax
#define swap(X,Y) { int t=X; X=Y; Y=t; }#define swap(X,Y) { int t=X; X=Y; Y=t; }
if (a>b) swap(a,b);
else b=0;
if (a>b) swap(a,b);
else b=0;*** parse error!
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Invocation Syntax
#define swap(X,Y) { int t=X; X=Y; Y=t; }#define swap(X,Y) { int t=X; X=Y; Y=t; }
if (a>b) swap(a,b);
else b=0;
if (a>b) swap(a,b);
else b=0;*** parse error!
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Invocation Syntax
#define swap(X,Y) { int t=X; X=Y; Y=t; }#define swap(X,Y) { int t=X; X=Y; Y=t; }
if (a>b) swap(a,b);
else b=0;
if (a>b) swap(a,b);
else b=0;*** parse error!
#define swap(X,Y) do { int t=X; X=Y; Y=t; } while (0)#define swap(X,Y) do { int t=X; X=Y; Y=t; } while (0)
if (a>b) swap(a,b);
else b=0;
if (a>b) swap(a,b);
else b=0;
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Invocation Syntax
• Problem: fixed invocation syntax!• same for exp / stm / …
#define swap(X,Y) { int t=X; X=Y; Y=t; }#define swap(X,Y) { int t=X; X=Y; Y=t; }
if (a>b) swap(a,b);
else b=0;
if (a>b) swap(a,b);
else b=0;*** parse error!
#define swap(X,Y) do { int t=X; X=Y; Y=t; } while (0)#define swap(X,Y) do { int t=X; X=Y; Y=t; } while (0)
if (a>b) swap(a,b);
else b=0;
if (a>b) swap(a,b);
else b=0;
M(x,y,z)M(x,y,z)
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Macro• MSYN: (AST)n AST, n 0
• Typed with nonterminals of the host grammar• Safe: no parse errors as a conseq. of expansion
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Macro• MSYN: (AST)n AST, n 0
• Typed with nonterminals of the host grammar• Safe: no parse errors as a conseq. of expansion
stm repeat stm until ( exp ) ;stm repeat stm until ( exp ) ;
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Macro• MSYN: (AST)n AST, n 0
• Typed with nonterminals of the host grammar• Safe: no parse errors as a conseq. of expansion
macro <stm> repeat <stm S> until ( <exp E> ) ; ::= { { bool first = true;
while (first || !<E>) {
<S>
first = false;
} }
}
macro <stm> repeat <stm S> until ( <exp E> ) ; ::= { { bool first = true;
while (first || !<E>) {
<S>
first = false;
} }
}
stm repeat stm until ( exp ) ;stm repeat stm until ( exp ) ;
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Macro• MSYN: (AST)n AST, n 0
• Typed with nonterminals of the host grammar• Safe: no parse errors as a conseq. of expansion
macro <stm> repeat <stm S> until ( <exp E> ) ; ::= { { bool first = true;
while (first || !<E>) {
<S>
first = false;
} }
}
macro <stm> repeat <stm S> until ( <exp E> ) ; ::= { { bool first = true;
while (first || !<E>) {
<S>
first = false;
} }
}
1. Invocation syntax: grammar extension
stm repeat stm until ( exp ) ;stm repeat stm until ( exp ) ;
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Macro• MSYN: (AST)n AST, n 0
• Typed with nonterminals of the host grammar• Safe: no parse errors as a conseq. of expansion
macro <stm> repeat <stm S> until ( <exp E> ) ; ::= { { bool first = true;
while (first || !<E>) {
<S>
first = false;
} }
}
macro <stm> repeat <stm S> until ( <exp E> ) ; ::= { { bool first = true;
while (first || !<E>) {
<S>
first = false;
} }
}
1. Invocation syntax: grammar extension
2. Transformation: morphing into host syntax
stm repeat stm until ( exp ) ;stm repeat stm until ( exp ) ;
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility?
macro <decls> enum { <id X> }; ::= {…}macro <decls> enum { <id X>, <id Y> }; ::= {…} macro <decls> enum { <id X>, <id Y>, <id Z> }; ::= {…}
macro <decls> enum { <id X> }; ::= {…}macro <decls> enum { <id X>, <id Y> }; ::= {…} macro <decls> enum { <id X>, <id Y>, <id Z> }; ::= {…}
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility?
macro <decls> enum { <id X> }; ::= {…}macro <decls> enum { <id X>, <id Y> }; ::= {…} macro <decls> enum { <id X>, <id Y>, <id Z> }; ::= {…}
macro <decls> enum { <id X> }; ::= {…}macro <decls> enum { <id X>, <id Y> }; ::= {…} macro <decls> enum { <id X>, <id Y>, <id Z> }; ::= {…}
decls enum { id } ;
enum { id , id } ;
enum { id , id , id } ;
decls enum { id } ;
enum { id , id } ;
enum { id , id , id } ;
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility?
macro <decls> enum { <id X> }; ::= {…}macro <decls> enum { <id X>, <id Y> }; ::= {…} macro <decls> enum { <id X>, <id Y>, <id Z> }; ::= {…}
macro <decls> enum { <id X> }; ::= {…}macro <decls> enum { <id X>, <id Y> }; ::= {…} macro <decls> enum { <id X>, <id Y>, <id Z> }; ::= {…}
decls enum { id } ;
enum { id , id } ;
enum { id , id , id } ;
decls enum { id } ;
enum { id , id } ;
enum { id , id , id } ;
• Problems:• Only fixed (finite) arity• Highly redundant
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility
• [Scheme]:• special list constructor: “...”
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility
• [Scheme]:• special list constructor: “...”
decls ( enum id * )decls ( enum id * )
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility
• [Scheme]:• special list constructor: “...”
• [MS2]:• lists +/, options ?, tuples {…}, and
token-separated lists T
decls ( enum id * )decls ( enum id * )
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility
• [Scheme]:• special list constructor: “...”
• [MS2]:• lists +/, options ?, tuples {…}, and
token-separated lists T
decls ( enum id * )decls ( enum id * )
decls enum { id , } ;decls enum { id
, } ; ~ E-BNF
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility!
• Allow user-defined nonterminals(in invocation syntax):
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility!
• Allow user-defined nonterminals(in invocation syntax):
decls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Flexibility!
• Allow user-defined nonterminals(in invocation syntax):
• Transformation?• without compromising safety
decls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorphisms
• Our solution: Metamorphisms• Attach host nonterminals to a user-def’d nonterminal
metamorph <n> m();metamorph <n> m();
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorphisms
• Our solution: Metamorphisms• Attach host nonterminals to a user-def’d nonterminal
metamorph <n> m();
macro <stm> … <m: A> … ::= { … <A> … }
metamorph <n> m();
macro <stm> … <m: A> … ::= { … <A> … }
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorphisms
• Our solution: Metamorphisms• Attach host nonterminals to a user-def’d nonterminal• Specify morphing (into host syntax) inductively
metamorph <n> m();
macro <stm> … <m: A> … ::= { … <A> … }
metamorph <n> m();
macro <stm> … <m: A> … ::= { … <A> … }
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorphisms
• Our solution: Metamorphisms• Attach host nonterminals to a user-def’d nonterminal• Specify morphing (into host syntax) inductively
metamorph <n> m();
macro <stm> … <m: A> … ::= { … <A> … }
morph <m> … ::= { … }
metamorph <n> m();
macro <stm> … <m: A> … ::= { … <A> … }
morph <m> … ::= { … }
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorphisms
• Our solution: Metamorphisms• Attach host nonterminals to a user-def’d nonterminal• Specify morphing (into host syntax) inductively• Non-local transformations (multiple results)
metamorph <n> m();
macro <stm> … <m: A> … ::= { … <A> … }
morph <m> … ::= { … }
metamorph <n> m();
macro <stm> … <m: A> … ::= { … <A> … }
morph <m> … ::= { … }
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorphisms
• Our solution: Metamorphisms• Attach host nonterminals to a user-def’d nonterminal• Specify morphing (into host syntax) inductively• Non-local transformations (multiple results)
metamorph <n,n’> m();
macro <stm> … <m: A, B> … ::= { … <A> … <B> … }
morph <m> … ::= { … } { … }
metamorph <n,n’> m();
macro <stm> … <m: A, B> … ::= { … <A> … <B> … }
morph <m> … ::= { … } { … }
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Example: enumdecls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Example: enumdecls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
enum { x, y, z };enum { x, y, z }; const int x = 0;const int y = 1;const int z = 2;
const int x = 0;const int y = 1;const int z = 2;
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Example: enumdecls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
enum { x, y, z };enum { x, y, z }; const int x = 0;const int y = 1;const int z = 2;
const int x = 0;const int y = 1;const int z = 2;
• Without compile-time programminglanguage (with AST values)
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Example: enumdecls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
enum { x, y, z };enum { x, y, z };
int e = 0;const int x = e++;const int y = e++;const int z = e++;
int e = 0;const int x = e++;const int y = e++;const int z = e++;
• Without compile-time programminglanguage (with AST values)
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Example: enum
metamorph <decls> enums();metamorph <decls> enums();
decls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Example: enum
metamorph <decls> enums();
macro <decls> enum { <id X> <enums: Ds> } ; ::= { int e = 0;
const int <X> = e++;
<Ds>
}
metamorph <decls> enums();
macro <decls> enum { <id X> <enums: Ds> } ; ::= { int e = 0;
const int <X> = e++;
<Ds>
}
decls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Example: enum
metamorph <decls> enums();
macro <decls> enum { <id X> <enums: Ds> } ; ::= { int e = 0;
const int <X> = e++;
<Ds>
}
morph <enums> , <id X> <enums: Ds> ::= { const int <X> = e++;
<Ds>
}
metamorph <decls> enums();
macro <decls> enum { <id X> <enums: Ds> } ; ::= { int e = 0;
const int <X> = e++;
<Ds>
}
morph <enums> , <id X> <enums: Ds> ::= { const int <X> = e++;
<Ds>
}
decls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Example: enum
metamorph <decls> enums();
macro <decls> enum { <id X> <enums: Ds> } ; ::= { int e = 0;
const int <X> = e++;
<Ds>
}
morph <enums> , <id X> <enums: Ds> ::= { const int <X> = e++;
<Ds>
}
morph <enums> ::= { }
metamorph <decls> enums();
macro <decls> enum { <id X> <enums: Ds> } ; ::= { int e = 0;
const int <X> = e++;
<Ds>
}
morph <enums> , <id X> <enums: Ds> ::= { const int <X> = e++;
<Ds>
}
morph <enums> ::= { }
decls enum { id enums } ;
enums , id enums
decls enum { id enums } ;
enums , id enums
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
stm reserve ( res ) stm
res id res
stm reserve ( res ) stm
res id res
Metamorph Example: reserve
reserve ( a b c ) ...;reserve ( a b c ) ...;
acquire(a); acquire(b); acquire(c); ...; release(c); release(b);release(a);
acquire(a); acquire(b); acquire(c); ...; release(c); release(b);release(a);
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Multiple ResultsExample: reserve
metamorph <stms,stms> res();metamorph <stms,stms> res();
stm reserve ( res ) stm
res id res
stm reserve ( res ) stm
res id res
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Multiple ResultsExample: reserve
metamorph <stms,stms> res();
macro <stm> reserve ( <res: S1,S2> ) <stm S> ::= { { <S1> <S> <S2> }
}
metamorph <stms,stms> res();
macro <stm> reserve ( <res: S1,S2> ) <stm S> ::= { { <S1> <S> <S2> }
}
stm reserve ( res ) stm
res id res
stm reserve ( res ) stm
res id res
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Multiple ResultsExample: reserve
metamorph <stms,stms> res();
macro <stm> reserve ( <res: S1,S2> ) <stm S> ::= { { <S1> <S> <S2> }
}
morph <res> <id X> <res: S1,S2> ::= { acquire(<X>); <S1>
} {
<S2> release(<X>);
}
metamorph <stms,stms> res();
macro <stm> reserve ( <res: S1,S2> ) <stm S> ::= { { <S1> <S> <S2> }
}
morph <res> <id X> <res: S1,S2> ::= { acquire(<X>); <S1>
} {
<S2> release(<X>);
}
stm reserve ( res ) stm
res id res
stm reserve ( res ) stm
res id res
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Multiple ResultsExample: reserve
metamorph <stms,stms> res();
macro <stm> reserve ( <res: S1,S2> ) <stm S> ::= { { <S1> <S> <S2> }
}
morph <res> <id X> <res: S1,S2> ::= { acquire(<X>); <S1>
} {
<S2> release(<X>);
}
morph <res> ::= { } { }
metamorph <stms,stms> res();
macro <stm> reserve ( <res: S1,S2> ) <stm S> ::= { { <S1> <S> <S2> }
}
morph <res> <id X> <res: S1,S2> ::= { acquire(<X>); <S1>
} {
<S2> release(<X>);
}
morph <res> ::= { } { }
stm reserve ( res ) stm
res id res
stm reserve ( res ) stm
res id res
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Advantages
• Flexibility
• Safety
• Simplicity
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Advantages
• Flexibility:• Tree structures• Non-local transformations (multiple results)
• Safety
• Simplicity
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Advantages
• Flexibility:• Tree structures• Non-local transformations (multiple results)
• Safety:• No parse errors as a conseq. of macro expansion• Guaranteed termination
• Simplicity
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Advantages
• Flexibility:• Tree structures• Non-local transformations (multiple results)
• Safety:• No parse errors as a conseq. of macro expansion• Guaranteed termination
• Simplicity: • Based entirely on declarative concepts:
grammars and substitution
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
vDSL:very Domain Specific Languagestudies
course Math101
title “Mathematics 101”
2 point fall term
…
exclusions
Math101 <> MathA
Math102 <> MathB
prerequisites
Math101, Math102 < Math201, Math202, Math203
Math101, CS101 < CS202
studies
course Math101
title “Mathematics 101”
2 point fall term
…
exclusions
Math101 <> MathA
Math102 <> MathB
prerequisites
Math101, Math102 < Math201, Math202, Math203
Math101, CS101 < CS202
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Specificity Parsing
macro <exp> select <id I> from <exp E> where <exp E2>
macro <exp> select all from <exp E> where <exp E2>
macro <exp> select <id I> from <exp E> where <exp E2>
macro <exp> select all from <exp E> where <exp E2>
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Specificity Parsing
• Challenge rounds:– Select most specific productions (wrt. FIRST sets)
macro <exp> select <id I> from <exp E> where <exp E2>
macro <exp> select all from <exp E> where <exp E2>
macro <exp> select <id I> from <exp E> where <exp E2>
macro <exp> select all from <exp E> where <exp E2>
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Specificity Parsing
• Challenge rounds:– Select most specific productions (wrt. FIRST sets)
• Resolves many ambiguities• Independent of definition-order• Overloading• Avoids keywordification• Commit no branch explosion, no backtracking
macro <exp> select <id I> from <exp E> where <exp E2>
macro <exp> select all from <exp E> where <exp E2>
macro <exp> select <id I> from <exp E> where <exp E2>
macro <exp> select all from <exp E> where <exp E2>
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Related Work: Macro Survey• 8x Macro languages:
• { CPP, M4, TEX, Dylan, C++ Templates, Scheme, JTS, MS2 }
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Related Work: Macro Survey• 8x Macro languages:
• { CPP, M4, TEX, Dylan, C++ Templates, Scheme, JTS, MS2 }
• 31x Macro properties:• { Level of operation, Programmability, Definition scope,
Termination, Argument syntax, Error trailing, … }
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Related Work: Macro Survey• 8x Macro languages:
• { CPP, M4, TEX, Dylan, C++ Templates, Scheme, JTS, MS2 }
• 31x Macro properties:• { Level of operation, Programmability, Definition scope,
Termination, Argument syntax, Error trailing, … }
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Related Work
• “Extensible Syntax with Lexical Scoping” - by Cardelli, Matthes, and Abadi :
• Not a macro language, but a parser generator:– Target language (not host language)– Extend recompile parser
• Localized transformation only• Disjoint productions• Keywordification• Explicit alpha conversion
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Future Work: metafront
• Extensible syntax processor, based on:• Specificity parsing and• Metamorphic syntax macros:
metafront metafrontbase grammar: Lmacros: L+ Lprogram in L+
program in L
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Future Work: metafront
• Extensible syntax processor, based on:• Specificity parsing and• Metamorphic syntax macros:
• Safe transformation: L+ L
metafront metafrontbase grammar: Lmacros: L+ Lprogram in L+
program in L
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Future Work: metafront
• Extensible syntax processor, based on:• Specificity parsing and• Metamorphic syntax macros:
• Safe transformation: L+ L• Safe transformation: L’ L, (vDSL)
metafront metafrontbase grammar: Lmacros: L+ Lprogram in L+
program in L
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
ConclusionMetamorphic Syntax Macros is a…
• flexible• safe• simple
…way of Growing Languages
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
ConclusionMetamorphic Syntax Macros is a…
• flexible• safe• simple
…way of Growing Languages
Fully implemented in <bigwig> (language for developing interactive Web services)
http://www.brics.dk/bigwig/http://www.brics.dk/bigwig/
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
The End
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PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Pretty Printing & Error Reporting• Pretty Printing:
• Terminal printers:ASCII, LA EX, HTML(+/- expansion)
• Error Reporting:• stdout, HTML
*** symbol errors:*** test.wig:7: Identifier ‘inf’ not declared in macro argument ‘S’ in macro invocation ‘reader’ (test.wig:7) defined in [std.wigmac:44]
*** symbol errors:*** test.wig:7: Identifier ‘inf’ not declared in macro argument ‘S’ in macro invocation ‘reader’ (test.wig:7) defined in [std.wigmac:44]
T
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
-Conversion
macro <stm> repeat <stm S> until ( <exp E> ) ; ::= { {
bool first = true;
while (first || !<E>) {
<S>
first = false;
}
}
}
macro <stm> repeat <stm S> until ( <exp E> ) ; ::= { {
bool first = true;
while (first || !<E>) {
<S>
first = false;
}
}
}
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
-Conversion
metamorph <decls> enums();
macro <decls> enum { <id X> <enums: Ds> } ; ::= { int e = 0;
const int <X> = e++;
<Ds>
}
morph <enums> , <id X> <enums: Ds> ::= { const int <X> = e++;
<Ds>
}
morph <enums> ::= { }
metamorph <decls> enums();
macro <decls> enum { <id X> <enums: Ds> } ; ::= { int e = 0;
const int <X> = e++;
<Ds>
}
morph <enums> , <id X> <enums: Ds> ::= { const int <X> = e++;
<Ds>
}
morph <enums> ::= { }
decls : enum { id enums } ;
enums : , id enums
|
decls : enum { id enums } ;
enums : , id enums
|
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Example: switchmetamorph <stm> swb();
macro <stm> switch ( <exp E> ) { <swb: S> } ::= { { var x = <E>; <S>}}
morph <swb> case <exp E> : <stms Ss> break; <swb: S>::= { if (x==<E>) { <Ss> } else <S>}
morph <swb> case <exp E> : <stms Ss> break; ::= { if (x==<E>) { <Ss> }}
metamorph <stm> swb();
macro <stm> switch ( <exp E> ) { <swb: S> } ::= { { var x = <E>; <S>}}
morph <swb> case <exp E> : <stms Ss> break; <swb: S>::= { if (x==<E>) { <Ss> } else <S>}
morph <swb> case <exp E> : <stms Ss> break; ::= { if (x==<E>) { <Ss> }}
stm : switch ( exp ) { swb }
swb : case exp : stms break; swb
| case exp : stms break;
stm : switch ( exp ) { swb }
swb : case exp : stms break; swb
| case exp : stms break;
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Metamorph Wellformedness
• Check at definition time:• “no left recursion” (guarantees termination):
• “derivability” (metamorphisms must derive something finite) :
xlist xlist X
xlist xlist X
xlist X xlist
xlist X xlist
xlist X xlist
xlist X xlist
xlist X xlistxlist X xlist
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Representationmacro <ids> MXY ( <ids Is> ) ::= { X, <Is>, Y }
A, MXY(B, C), D A, X, B, C, Y, D
macro <ids> MXY ( <ids Is> ) ::= { X, <Is>, Y }
A, MXY(B, C), D A, X, B, C, Y, D
• “Weaving” yields transparency!
weave
PEPM 2002 Growing Languages with Metamorphic Syntax Macros January 14, 2002
Syntax Macros
• MSYN: (AST)n AST , n 0
~
square( )
macro <exp> square ( <exp E> ) ::= { <E> * <E>
}
macro <exp> square ( <exp E> ) ::= { <E> * <E>
}**
exp
exp
Eexp
E
**
exp
y + 1y
+ 1 y + 1y
+ 1
exp
Eexp
Ey
+ 1y + 1
exp