Download The Evolution of Programs by Nachum Dershowitz (auth.) PDF

By Nachum Dershowitz (auth.)

-Ecclesiastes 12:12 courses are perpetually subjected to many rorms or transrormation. After an preliminary model of a application has been designed and constructed, it undergoes debugging and certification. furthermore, such a lot long-lived professional­ grams have a liCe-cycle that comes with changes to satisfy amended requisites and extensions for elevated services. Such evolution­ ary facets of programming are the subject of this monograph. We current rormal tools for manipulating courses and illustrate their applica­ tion with various examples. Such equipment will be included in semi-automated programming environments, the place they'd serve to ease the load at the programmer. we commence through describing a style wherein a given software that achieves one target may be converted to accomplish a unique aim or a professional­ gram that computes fallacious effects should be debugged to accomplish the two Preface meant effects. The abstraction of a collection of cognate courses to acquire a application schema, and the instantiation of summary schemata to resolve concrete difficulties, are approached from an identical standpoint. moreover, we describe synthesis ideas for producing code from requirements and annotation principles for making assertions approximately code. The synthesis principles can be used while a application is first being constructed, or while, during editing a application, it is advisable to rewrite a application phase. Annotation ideas can be used for the aim of picking out what an wrong application fairly does earlier than trying to debug it or how an accurate application works prior to trying to alter it.

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Extra resources for The Evolution of Programs

Sample text

G. [Knuth74], [Gerhart75a]. [Gerhart75b], [Bauer76], [DarlingtonBursta1l76], [StandishKiblerNeighbors76], [Wegbreit76], [Schwartz77], [Loveman77]. [Blikle7S], [BalzerSl], and [BroyPepperSl]). Modification differs from such transformations in that correctness with respect to the original specification is not preserved. What we want is for the resultant program to be correct with respect to a transformed specification. Correctness-preserving transformations and specification-changing modifications are thus complementary.

Instead, certain properties specific to the function min were used in the construction of the program, properties that do not, however, hold for the new function max. Later, we shall see how such a situation can be dealt with. 64 Program Modification and Debugging In the meantime, we can effect the desired transformation 9 A[0]=min{A[n:2'nj} A[0]=max{A[n:2'nj} in another way. We first look for an equivalent formulation of the specifications that highlights an alternative analogy. For example, the function max{A} can be replaced by the equivalent -mint-A}, where - A denotes the array A with each element negated.

We show now how code to achieve these subgoals may be synthesized. The first subgoal is a conjunction of two relations, z2 ~ a and a < (z+ s )2, which are to be achieved simultaneously. It may be split into the two consecutive subgoals purpose z2 ~ a, a < (z + S )2 achieve z2 ~ a varying z achieve a < (z + s)2 varying s assert z2~ a, a «z+s)2. The first sets the variable z to some value satisfying z2 ~ a; the second leaves z constant so that z2 ~ a remains true, while setting s to some value satisfying a < (z+ s )2.

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