Usable Synthesis Sumit Gulwani Microsoft Research, Redmond Usable Verification Workshop November 2010 MSR Redmond

What is Program Synthesis? –Synthesize an executable program from user intent expressed in form of some constraints. 1 Automated Program Synthesis Why today? –Natural goal given that computing has become accessible, but: fundamental “how” programming models have not changed. most people are not expert programmers. –Enabling technology is now available Better search/logical reasoning techniques (SAT/SMT solvers) Faster machines (good application for multi-cores) State of the art: We can synthesize lines of code.

Technical Dimensions –Search Space –Search Technique Usability Dimensions –Impact Who will find it useful? How useful would it be? –Intent Expression Mechanism How will they express their intent? 2 Dimensions in Program Synthesis

Search Space: Straight-line programs that use –Arithmetic Operators: +,-,*,/ –Logical Operators: Bitwise and/or/not, Shift left/right Search Algorithm: SAT/SMT based techniques 3 Application 1: Bitvector Algorithms Joint work with: Susmit Jha, Sanjit Seshia (UC-Berkeley), Ashish Tiwari (SRI) and Venkie (MSR Redmond) Paper: ICSE 2010

Turn-off rightmost 1-bit 4 Examples of Bitvector Algorithms Z Z & (Z-1) Z Z & Z & (Z-1)

5 Examples of Bitvector Algorithms Turn-off rightmost contiguous sequence of 1-bits Z Z & (1 + (Z | (Z-1))) Ceil of average of two integers without overflowing (Y|Z) – ((Y © Z) >> 1)

6 Examples of Bitvector Algorithms P25: Higher order half of product of x and y o1 := and(x,0xFFFF); o2 := shr(x,16); o3 := and(y,0xFFFF); o4 := shr(y,16); o5 := mul(o1,o3); o6 := mul(o2,o3); o7 := mul(o1,o4); o8 := mul(o2,o4); o9 := shr(o5,16); o10 := add(o6,o9); o11 := and(o10,0xFFFF); o12 := shr(o10,16); o13 := add(o7,o11); o14 := shr(o13,16); o15 := add(o14,o12); res := add(o15,o8); P24: Round up to next highest power of 2 o1 := sub(x,1); o2 := shr(o1,1); o3 := or(o1,o2); o4 := shr(o3,2); o5 := or(o3,o4); o6 := shr(o5,4); o7 := or(o5,o6); o8 := shr(o7,8); o9 := or(o7,o8); o10 := shr(o9,16); o11 := or(o9,o10); res := add(o10,1);

Algorithm Designers Impact: Algorithm Designers or Software Developers Intent Expression Mechanism: Logical Specifications Consumers of Program Synthesis Technology Bitvector Algorithms: Usability Dimensions 7 Software Developers

Search Space: Programs with conditionals/loops –String operations: Concatenate, Substring –Logical operations: comparison involving # of occurrences of a regular expression Search Algorithm: Combination of –Version Space Algebras –Machine Learning 8 Application 2: String Manipulation Macros Joint work with: Bill Harris (UW, Madison), Rishabh Singh (MIT) Paper: POPL 2011

End-Users Algorithm Designers Software Developers Consumers of Program Synthesis Technology String Manipulation Macros: Usability Dimensions Impact: End-users Intent Expression Mechanism: Input-output Examples 9 Most Useful Target

10 String Manipulation Macros Excel Demo

1.Identify tasks that end-users struggle with and identify how they can effectively communicate their intent. –Read help-forums and blogs. –Interview real users. 2.Design a language that satisfies the following trade-off. –Expressive enough to express a lot of tasks. –Small enough to allow efficient learning. 3.Design a learning algorithm with following features. –Interactive with fast convergence (with success or failure). –Provide feedback. –Noise tolerant. 11 Methodology: Automating end-user programming

Search Space: Straight-line programs –Operations: Ruler, Compass Search Algorithm: Exhaustive Search –Property Testing –Goal-directed search –Commonly used library of constructions 12 Application 3: Geometry Constructions Joint work with: Kalika Bali, Monojit Chaudhuri (MSR Bangalore) Vijay Korthikanti (UIUC), Ashish Tiwari (SRI) Ken McMillan (MSR Redmond)

Programming Language for Geometry –Objects: Point, Line, Circle –Constructors Ruler(Point, Point) -> Line Compass(Point, Point) -> Circle Intersect(Circle, Circle) -> Pair of Points Intersect(Line, Circle) -> Pair of Points Intersect(Line, Line) -> Point Logic for Geometry –Inequality predicates over arithmetic expressions Distance(Point, Point), Angle(Line, Line), … Automated Problem Solving –Given pre/postcondition, synthesize a straight-line program 13 Geometry Constructions: Role of PL/logic/synthesis

Automated Problem Solving Given pre/postcondition, synthesize a straight-line program Example: Draw a line L’ perpendicular to a given line L. Precondition: true Postcondition: Angle(L’,L) = 90 Program Step 1: P1, P2 = ChoosePoint(L); Step 2: C1 = Circle(P1,P2); Step 3: C2 = Circle(P2,P1); Step 4: = Intersect(C1,C2); Step 5: L’ = Line(P3,P4); 14 Geometry Domain: Automated Problem Solving

15 Constructing line L’ perpendicular to given line L P1 P2 P3 P4 C1 C2 L L’ Step 1: P1, P2 = ChoosePoint(L); Step 2: C1 = Circle(P1,P2); Step 3: C2 = Circle(P2,P1); Step 4: = Intersect(C1,C2); Step 5: L’ = Line(P3,P4);

Bisect a given line. Bisect an angle. Copy an angle. Draw a line parallel to a given line. Draw an equilateral triangle given two points. Draw a regular hexagon given a side. Given 4 points, draw a square with each of the sides passing through a different point. Other Applications: New approximate geometric constructions 2D/3D planning problems 16 Examples of Geometry Constructions

Students and Teachers End-Users Algorithm Designers Software Developers Consumers of Program Synthesis Technology Geometry Constructions: Usability Dimensions Impact: Students and Teachers Intent Expression Mechanism: Natural Language 17 Most Trans- formational Target Most Useful Target

Automating Education Make education interactive and fun Automated problem solving (for students) –Provide hints –Point out mistakes and suggest fixes Creation of teaching material (for teachers) –Authoring tools –Problem construction Group interaction (for teachers/students) –Ask questions –Share annotations Domains: Geometry, Algebra, Probability, Mechanics, Electrical Circuits, etc. 18

Students and Teachers End-Users Algorithm Designers Software Developers Most Trans- formational Target Usability Dimensions 19 Consumers of Program Synthesis Technology Most Useful Target Logic Examples English Impact User Interface

Dimensions in Program Synthesis –Invited Tutorial at FMCAD 2010 –Invited paper at PPDP 2010 Bitvector Algorithms –“Oracle guided component based program synthesis”, ICSE 2010, Jha/Gulwani/Seshia/Tiwari String Manipulation Macros –“Automating String Processing in Spreadsheets using Input- Output Examples”, POPL 2011, Gulwani Geometry Constructions –“Synthesizing Geometry Constructions”, Techreport 2011, Gulwani/Korthikanti/Tiwari 20 References