Saffron
August 31, 1988
Saffron

James Rauen
August 31, 1988
Why another Cedar compiler?
· Demonstrate the viability of Casaba
· Principled implementation
Easy to maintain
Easy to verify
· Type theory
· Experiments
What is Cedar?
· CLRM
· Mesa manual
· The implementation
· Religion
Saffron
· Front end of a compiler
· Implements Cedar/Mesa ± Religion
· Implemented in Casaba
Environment
<< [Artwork node; type 'Artwork on' to command tool] >>
Context Tree
· Mimics lexical structure of source program
· Each node has a TGN.  TGN describes runtime type structure of all the statically linked frames.
Parser
· Concrete Grammar
· Abstract Grammar
Context Tree
A data structure which mimics the lexical structure of a program
· Context Tree
· Program Graph
What Saffron Does
· Type Graph
· Context Tree
· Program Graph
Weird Cedar I
    a: INT _ b;        a: INT = b;
    b: INT _ a;        b: INT = a;

    a: INT = b;        a: INT _ b;
    b: INT _ a;        b: INT = a;
Weird Cedar II
    a: INT _ b;        a: INT = b;
    b: INT _ 3;        b: INT = 3;

    a: INT = b;        a: INT _ b;
    b: INT _ 3;        b: INT = 3;
Into the Abyss
Three Innocuous Features
· Sequential processing of declarations
· Dependency analysis among named constants with compile-time values
· INLINE does not affect  the meaning of a program,  except maybe to make it illegal
Weird Cedar III
Foo1: CEDAR PROGRAM = BEGIN
Three: PROC RETURNS [INT] = 
INLINE { RETURN[3] };
a: INT = b;
b: INT = Three[];
c: INT _ a;
END.
Weird Cedar IV
    Foo: TYPE = INT[0..LAST[Bar]];
    Bar: TYPE = INT[FIRST[Foo]..10];
    x: INT _ FIRST[Bar];
Out of the Abyss
Dependency Graph
Nodes for:
· Values of named compile-time constants
· Bodies of inline procedures 
· Initialization expressions of types 
· SIZE, FIRST, LAST properties of types 
Topological Sort
Reject circular dependency graph

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