Resugaring: Lifting Evaluation Sequences through Syntactic Sugar - PowerPoint PPT Presentation

Resugaring: Lifting Evaluation Sequences through Syntactic Sugar Justin Pombrio, Shriram Krishnamurthi Brown University

Syntactic Sugar 2

Syntactic Sugar desugar x + 2 x . _ _ a d d _ _ ( 2 ) 3

Syntactic Sugar desugar x + 2 x . _ _ a d d _ _ ( 2 ) desugar [ x * x | x < - l s t ] m a p ( \ x - > x * x ) l s t 4

Syntactic Sugar desugar x + 2 x . _ _ a d d _ _ ( 2 ) desugar [ x * x | x < - l s t ] m a p ( \ x - > x * x ) l s t desugar x o r y l e t t = x i n i f t t h e n t e l s e y 5

Surface language (what you write) Syntactic Sugar desugar x + 2 x . _ _ a d d _ _ ( 2 ) desugar [ x * x | x < - l s t ] m a p ( \ x - > x * x ) l s t desugar x o r y l e t t = x i n i f t t h e n t e l s e y 6

Surface language Core language (what you write) (what runs) Syntactic Sugar desugar x + 2 x . _ _ a d d _ _ ( 2 ) desugar [ x * x | x < - l s t ] m a p ( \ x - > x * x ) l s t desugar x o r y l e t t = x i n i f t t h e n t e l s e y 7

Big surface language desugar Small core 8

Big surface language desugar Small core 9

Big surface language desugar Code analyzer Small Refactoring engine core Evaluator 10

Big surface language desugar Code analyzer Small Refactoring engine core Evaluator 11

Big surface language desugar Code analyzer Small Refactoring engine core Evaluator Evaluator 12

Surface Core n o t ( t r u e ) o r t r u e 13

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e 14

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e l e t t = f a l s e i n i f t t h e n t e l s e t r u e i f f a l s e t h e n f a l s e e l s e t r u e t r u e 15

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e f a l s e o r t r u e l e t t = f a l s e i n i f t t h e n t e l s e t r u e i f f a l s e t h e n f a l s e e l s e t r u e t r u e t r u e 16

Confection core eval seq → surface eval seq 17

18

92 steps 19

92 steps 7 steps 20

Surface Core n o t ( t r u e ) o r t r u e Resugaring: Running sugar in reverse 21

Surface Core n o t ( t r u e ) o r t r u e f a l s e o r t r u e t r u e Resugaring: Running sugar in reverse 22

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e f a l s e o r t r u e t r u e Resugaring: Running sugar in reverse 23

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e f a l s e o r t r u e l e t t = f a l s e i n i f t t h e n t e l s e t r u e i f f a l s e t h e n f a l s e e l s e t r u e t r u e t r u e Resugaring: Running sugar in reverse 24

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n resugar i f t t h e n t e l s e t r u e f a l s e o r t r u e l e t t = f a l s e i n i f t t h e n t e l s e t r u e i f f a l s e t h e n f a l s e e l s e t r u e t r u e t r u e Resugaring: Running sugar in reverse 25

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n resugar i f t t h e n t e l s e t r u e resugar f a l s e o r t r u e l e t t = f a l s e i n i f t t h e n t e l s e t r u e i f f a l s e t h e n f a l s e e l s e t r u e t r u e t r u e Resugaring: Running sugar in reverse 26

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n resugar i f t t h e n t e l s e t r u e resugar f a l s e o r t r u e l e t t = f a l s e i n i f t t h e n t e l s e t r u e resugar i f f a l s e t h e n f a l s e e l s e t r u e t r u e t r u e Resugaring: Running sugar in reverse 27

THREE KEY PROPERTIES OF RESUGARING 28

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e resugar l e t t = f a l s e i n i f t t h e n t e l s e t r u e 29

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e resugar t r u e o r t r u e l e t t = f a l s e i n o r t r u e i f t t h e n t e l s e t r u e 30

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e resugar t r u e o r t r u e l e t t = f a l s e i n o r t r u e i f t t h e n t e l s e t r u e Emulation Each surface term must desugar to the core term it purports to represent 31

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e resugar l e t t = f a l s e i n i f t t h e n t e l s e t r u e 32

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e resugar l e t t = f a l s e i n l e t t = f a l s e i n i f t t h e n t e l s e t r u e i f t t h e n t e l s e t r u e 33

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e resugar l e t t = f a l s e i n l e t t = f a l s e i n i f t t h e n t e l s e t r u e i f t t h e n t e l s e t r u e Abstraction Show things in terms of a sugar precisely when the programmer used that sugar. 34

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e resugar l e t t = f a l s e i n i f t t h e n t e l s e t r u e resugar i f f a l s e t h e n f a l s e e l s e t r u e resugar t r u e t r u e 35

Surface Core desugar n o t ( t r u e ) o r t r u e l e t t = n o t ( t r u e ) i n i f t t h e n t e l s e t r u e resugar Coverage l e t t = f a l s e i n i f t t h e n t e l s e t r u e Show as many steps resugar as possible i f f a l s e t h e n f a l s e e l s e t r u e resugar t r u e t r u e 36

x o r y - > l e t t = x i n i f t t h e n t e l s e y 37

expand match substitute x o r y - > l e t t = x i n i f t t h e n t e l s e y 38

expand match substitute x o r y - > l e t t = x i n i f t t h e n t e l s e y substitute match unexpand 39

A Little Theory expand : Surf Term → Core Term unexpand : Core Term × Surf Term → Surf Term 40

A Little Theory expand : Surf Term → Core Term unexpand : Core Term × Surf Term → Surf Term It's a lens! 41

A Little Theory expand : Surf Term → Core Term unexpand : Core Term × Surf Term → Surf Term It's a lens! unexpand (expand T) T = T GetPut GetPut expand (unexpand T’ T) = T’ PutGet PutGet 42

A Little Theory expand : Surf Term → Core Term unexpand : Core Term × Surf Term → Surf Term It's a lens! unexpand (expand T) T = T GetPut GetPut expand (unexpand T’ T) = T’ PutGet PutGet Well-formedness criteria on rules ensure these laws. 43

Key Properties Emulation Abstraction Coverage 44

Key Properties Emulation (Lens Laws) Abstraction Coverage 45

Key Properties Emulation (Lens Laws) Abstraction (T agging – see paper) Coverage 46

Key Properties Emulation (Lens Laws) Abstraction (T agging – see paper) Coverage (Empirical) 47

A WORKING SYSTEM 48

92 steps 7 steps 49

Surface Core ( o r ( a n d # t # f ) # f ) 50