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Program Transformation

Program Transformation. Application examples. Converting to a new language dialect Migrating from a procedural language to an object-oriented one, e.g. C to C++ Adding code comments Requirement upgrading, e.g. using 4 digits for years instead of 2 (Y2K)

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Program Transformation

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  1. Program Transformation

  2. Application examples • Converting to a new language dialect • Migrating from a procedural language to an object-oriented one, e.g. C to C++ • Adding code comments • Requirement upgrading, e.g. using 4 digits for years instead of 2 (Y2K) • Structural improvements, e.g. changing GOTOs to control structures • Pretty printing COSC6431

  3. Simple program transformation • Modify all arithmetic expressions to reduce the number of parentheses using the formula: (a+b)*c = a*c + b*cx := (2+5)*3becomesx := 2*3 + 5*3 COSC6431

  4. Transformation tools • There are many transformation tools • Program-Transformation.org lists about 90 of them • We will look at one of the most mature tools, TXL COSC6431

  5. TXL • A generalized source-to-source translation system • Uses a context-free grammar to describe the structures to be transformed • Rule specification uses a by-example style • Has been used to process billions of lines of code for Y2K purposes COSC6431

  6. TXL programs • TXL programs consist of two parts: • Grammar for the input language • Transformation Rules • Let’s look at some examples… COSC6431

  7. % Part I. Syntax specification define program [expression] end define define expression [term] | [expression] [addop] [term] end define define term [primary] | [term] [mulop] [primary] end define define primary [number] | ( [expression] ) end define define addop '+ | '- end define define mulop '* | '/ end define Calculator.Txl - Grammar COSC6431

  8. % Part 2. Transformation rules rule main replace [expression] E [expression] construct NewE [expression] E [resolveAddition] [resolveSubtraction] [resolveMultiplication] [resolveDivision] [resolveParentheses] where not NewE [= E] by NewE end rule rule resolveAddition replace [expression] N1 [number] + N2 [number] by N1 [+ N2] end rule rule resolveSubtraction … rule resolveMultiplication … rule resolveDivision … rule resolveParentheses replace [primary] ( N [number] ) by N end rule Calculator.Txl - Rules COSC6431

  9. % Form the dot product of two vectors, % e.g., (1 2 3).(3 2 1) => 10 define program ( [repeat number] ) . ( [repeat number] ) | [number] end define rule main replace [program] ( V1 [repeat number] ) . ( V2 [repeat number] ) construct Zero [number] 0 by Zero [addDotProduct V1 V2] end rule rule addDotProduct V1 [repeat number] V2 [repeat number] deconstruct V1 First1 [number] Rest1 [repeat number] deconstruct V2 First2 [number] Rest2 [repeat number] construct ProductOfFirsts [number] First1 [* First2] replace [number] N [number] by N [+ ProductOfFirsts] [addDotProduct Rest1 Rest2] end rule DotProduct.Txl COSC6431

  10. Sort.Txl % Sort.Txl - simple numeric bubble sort define program [repeat number] end define rule main replace [repeat number] N1 [number] N2 [number] Rest [repeat number] where N1 [> N2] by N2 N1 Rest end rule COSC6431

  11. www.txl.ca • Guided Tour • Many examples • Reference manual • Download TXL for many platforms COSC6431

  12. Example uses • HTML Pretty Printing of Source Code • Language to Language Translation • Design Recovery from Source • Improvement of security problems • Program instrumentation and measurement • Logical formula simplification and interpretation. COSC6431

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