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Languages and Compilers(SProg og Oversættere)

Lecture 13 (2)

Bent Thomsen

Department of Computer Science

Aalborg University

With acknowledgement to Hanne Riis Nielson and Flemming Nielson whose book this lecture is based on.

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The missing link

The connectionbetween

Syntax and Semanticsand

Languages and Compilers

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The Language While

The Language While can be considered a mini version of Mini TriangleWhile is almost the same as the BIMS language

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Single step operational semantics for While

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Recursive Interpreter and Semantics

public Object visitBinaryExpression(BinaryExpression expr, Object arg){

Value val1 = (Value) expr.E1.visit(this, null);Value val2 = (Value) expr.E2.visit(this, null);

return applyBinary(expr.O, val1, val2);}

• Code for Recursive Interpreter can be derived from big step semantics

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A stack based virtual machine - AM

States:

Transitions:

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Operational semantics for AM

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Translation of While to AM

Note similarity with code generation templates for Mini Triangle

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Example

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Correctness Proof

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Soundness and completeness

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Getting closer to TAM

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And closer

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Conclusion

• With a bit of hard work it is possible to connect – The high level operational semantics for a language

– With the low level implementation

– And prove correctness of the translation

• This is called:

Provably correct implementations

• For more information read– Semantics with applications,

– Hanne Riis Nielson and Flemming Nielson

– Wiley 1992, ISBN 0 471 92980 8