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

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Resugaring: Lifting Evaluation Sequences through Syntactic Sugar

Justin Pombrio, Shriram Krishnamurthi Brown University

SLIDE 2

2

Syntactic Sugar

SLIDE 3

3

Syntactic Sugar

desugar

x + 2 x . _ _ a d d _ _ ( 2 )

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4

Syntactic Sugar

desugar desugar

x + 2 x . _ _ a d d _ _ ( 2 ) [ x * x | x <

l

s t ] m a p ( \ x

>

x * x ) l s t

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5

Syntactic Sugar

desugar desugar desugar

x + 2 x . _ _ a d d _ _ ( 2 ) [ x * x | x <

l

s t ] m a p ( \ x

>

x * x ) l s t x

r

y l e t t = x i n i f t t h e n t e l s e y

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6

Syntactic Sugar

Surface language (what you write)

desugar desugar desugar

x + 2 x . _ _ a d d _ _ ( 2 ) [ x * x | x <

l

s t ] m a p ( \ x

>

x * x ) l s t x

r

y l e t t = x i n i f t t h e n t e l s e y

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7

Syntactic Sugar

Surface language (what you write) Core language (what runs)

desugar desugar desugar

x + 2 x . _ _ a d d _ _ ( 2 ) [ x * x | x <

l

s t ] m a p ( \ x

>

x * x ) l s t x

r

y l e t t = x i n i f t t h e n t e l s e y

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8

Big surface language Small core

desugar

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9

Big surface language Small core

desugar

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10

Code analyzer Refactoring engine Evaluator Big surface language Small core

desugar

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11

Code analyzer Refactoring engine Evaluator Big surface language Small core

desugar

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12

Code analyzer Refactoring engine Evaluator Big surface language Small core Evaluator

desugar

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13

Core Surface

n

t

( t r u e )

r

t r u e

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14

Core Surface

desugar

n

t

( t r u e )

r

t r u e l e t t = n

t

( t r u e ) i n i f t t h e n t e l s e t r u e

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15

Core Surface

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

desugar

n

t

( t r u e )

r

t r u e l e t t = n

t

( t r u e ) i n i f t t h e n t e l s e t r u e

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16

Core Surface

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 f a l s e

r

t r u e t r u e

desugar

n

t

( t r u e )

r

t r u e l e t t = n

t

( t r u e ) i n i f t t h e n t e l s e t r u e

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17

Confection

core eval seq surface eval seq →

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18

SLIDE 19

19

92 steps

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20

92 steps 7 steps

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21

Core Surface Resugaring: Running sugar in reverse

n

t

( t r u e )

r

t r u e

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22

Core Surface Resugaring: Running sugar in reverse

n

t

( t r u e )

r

t r u e f a l s e

r

t r u e t r u e

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23

Core Surface

desugar

Resugaring: Running sugar in reverse

n

t

( t r u e )

r

t r u e f a l s e

r

t r u e t r u e l e t t = n

t

( t r u e ) i n i f t t h e n t e l s e t r u e

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24

Core Surface

desugar

Resugaring: Running sugar in reverse

n

t

( t r u e )

r

t r u e f a l s e

r

t r u e t r u e l e t t = n

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

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25

Core Surface

desugar

Resugaring: Running sugar in reverse

resugar

n

t

( t r u e )

r

t r u e f a l s e

r

t r u e t r u e l e t t = n

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

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26

Core Surface

desugar resugar

Resugaring: Running sugar in reverse

resugar

n

t

( t r u e )

r

t r u e f a l s e

r

t r u e t r u e l e t t = n

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

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27

Core Surface

desugar resugar

Resugaring: Running sugar in reverse

resugar resugar

n

t

( t r u e )

r

t r u e f a l s e

r

t r u e t r u e l e t t = n

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

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28

THREE KEY PROPERTIES OF RESUGARING

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29

Core Surface

l e t t = n

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

desugar resugar

n

t

( t r u e )

r

t r u e

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30

Core Surface

l e t t = n

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

desugar resugar

n

t

( t r u e )

r

t r u e t r u e

r

t r u e

r

t r u e

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31

Core Surface

l e t t = n

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

desugar resugar

n

t

( t r u e )

r

t r u e Emulation

Each surface term must desugar to the core term it purports to represent

t r u e

r

t r u e

r

t r u e

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32

Core Surface

l e t t = n

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

desugar resugar

n

t

( t r u e )

r

t r u e

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33

Core Surface

l e t t = n

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 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

desugar resugar

n

t

( t r u e )

r

t r u e

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34

Core Surface

l e t t = n

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 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 Abstraction

Show things in terms of a sugar precisely when the programmer used that sugar. desugar resugar

n

t

( t r u e )

r

t r u e

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35

Core Surface

l e t t = n

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 n

t

( t r u e )

r

t r u e t r u e

desugar resugar resugar resugar

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36

Core Surface

l e t t = n

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 n

t

( t r u e )

r

t r u e t r u e Coverage

Show as many steps as possible desugar resugar resugar resugar

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37

x

r

y

>

l e t t = x i n i f t t h e n t e l s e y

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38

x

r

y

>

l e t t = x i n i f t t h e n t e l s e y

expand

match substitute

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39

x

r

y

>

l e t t = x i n i f t t h e n t e l s e y

expand unexpand

match substitute match substitute

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40

A Little Theory

expand : Surf Term Core Term → unexpand : Core Term × Surf Term Surf Term →

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41

A Little Theory

expand : Surf Term Core Term → unexpand : Core Term × Surf Term Surf Term →

It's a lens!

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42

A Little Theory

expand : Surf Term Core Term → unexpand : Core Term × Surf Term Surf Term →

It's a lens! GetPut PutGet

unexpand (expand T) T = T expand (unexpand T’ T) = T’

GetPut PutGet

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43

A Little Theory

expand : Surf Term Core Term → unexpand : Core Term × Surf Term Surf Term →

It's a lens! Well-formedness criteria on rules ensure these laws. GetPut PutGet

unexpand (expand T) T = T expand (unexpand T’ T) = T’

GetPut PutGet

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44

Key Properties

Emulation Abstraction Coverage

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45

Key Properties

Emulation (Lens Laws) Abstraction Coverage

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46

Key Properties

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

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47

Key Properties

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

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48

A WORKING SYSTEM

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49

92 steps 7 steps

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50

Core Surface

(

r

( a n d # t # f ) # f )

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51

Core Surface

desugar (

r

( a n d # t # f ) # f ) ( ( l a m b d a ( t ) ( b e g i n ( i f t t ( ( l a m b d a ( ) # f ) ) ) ) ) ( i f # t ( ( l a m b d a ( ) # f ) ) # f ) )

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52 ( ( l a m b d a ( t ) ( b e g i n ( i f t t ( ( l a m b d a ( ) # f ) ) ) ) ) ( ( l a m b d a ( ) # f ) ) ) ( ( l a m b d a ( t ) ( b e g i n ( i f t t ( ( l a m b d a ( ) # f ) ) ) ) ) # f ) ( i f # f t ( ( l a m b d a ( ) # f ) ) ) ( ( l a m b d a ( ) # f ) ) # f

Core Surface

desugar (

r

( a n d # t # f ) # f ) ( ( l a m b d a ( t ) ( b e g i n ( i f t t ( ( l a m b d a ( ) # f ) ) ) ) ) ( i f # t ( ( l a m b d a ( ) # f ) ) # f ) )

SLIDE 53

53 (

r

# f # f ) (

r

# f ) # f ( ( l a m b d a ( t ) ( b e g i n ( i f t t ( ( l a m b d a ( ) # f ) ) ) ) ) ( ( l a m b d a ( ) # f ) ) ) ( ( l a m b d a ( t ) ( b e g i n ( i f t t ( ( l a m b d a ( ) # f ) ) ) ) ) # f ) ( i f # f t ( ( l a m b d a ( ) # f ) ) ) ( ( l a m b d a ( ) # f ) ) # f

Core Surface

desugar (

r

( a n d # t # f ) # f ) ( ( l a m b d a ( t ) ( b e g i n ( i f t t ( ( l a m b d a ( ) # f ) ) ) ) ) ( i f # t ( ( l a m b d a ( ) # f ) ) # f ) )

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54

Core Surface

m y

l

i s t = [ 2 ] c a s e s ( L i s t ) m y

l

i s t : | e m p t y ( ) = > p r i n t ( " e m p t y " ) | l i n k ( s

m

e t h i n g , _ ) = > p r i n t ( " n

t

e m p t y " ) e n d

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55

Core Surface

desugar

m y

l

i s t = l i s t . [ " l i n k " ] ( 2 , l i s t . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = [ 2 ] c a s e s ( L i s t ) m y

l

i s t : | e m p t y ( ) = > p r i n t ( " e m p t y " ) | l i n k ( s

m

e t h i n g , _ ) = > p r i n t ( " n

t

e m p t y " ) e n d

SLIDE 56

56

m y

l

i s t =

b

j . [ " l i n k " ] ( 2 , l i s t . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t =

b

j . [ " l i n k " ] ( 2 , l i s t . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = < f u n c > ( 2 , l i s t . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = < f u n c > ( 2 ,

b

j . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = < f u n c > ( 2 ,

b

j . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = < f u n c > ( 2 , [ ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = [ 2 ] b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d t e m p M O D R I O U J : : L i s t = [ 2 ] t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) [ 2 ] . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) [ 2 ] . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) < f u n c > ( { " e m p t y " : f u n ( ) : e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) < f u n c > ( { " e m p t y " : f u n ( ) : e n d , " l i n k " : f u n ( ) : e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) < f u n c > (

b

j , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) < f u n c > (

b

j , f u n ( ) : e n d ) < f u n c > ( " n

t

e m p t y " ) " n

t

e m p t y "

Core Surface

desugar

m y

l

i s t = l i s t . [ " l i n k " ] ( 2 , l i s t . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = [ 2 ] c a s e s ( L i s t ) m y

l

i s t : | e m p t y ( ) = > p r i n t ( " e m p t y " ) | l i n k ( s

m

e t h i n g , _ ) = > p r i n t ( " n

t

e m p t y " ) e n d

SLIDE 57

57

m y

l

i s t = [ 2 ] c a s e s ( L i s t ) m y

l

i s t : | e m p t y ( ) = > p r i n t ( " e m p t y " ) | l i n k ( s

m

e t h i n g , _ ) = > p r i n t ( " n

t

e m p t y " ) e n d c a s e s ( L i s t ) [ 2 ] : | e m p t y ( ) = > p r i n t ( " e m p t y " ) | l i n k ( s

m

e t h i n g , _ ) = > p r i n t ( " n

t

e m p t y " ) e n d < f u n c > ( " n

t

e m p t y " ) " n

t

e m p t y "

m y

l

i s t =

b

j . [ " l i n k " ] ( 2 , l i s t . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t =

b

j . [ " l i n k " ] ( 2 , l i s t . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = < f u n c > ( 2 , l i s t . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = < f u n c > ( 2 ,

b

j . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = < f u n c > ( 2 ,

b

j . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = < f u n c > ( 2 , [ ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = [ 2 ] b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d t e m p M O D R I O U J : : L i s t = [ 2 ] t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) [ 2 ] . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) [ 2 ] . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) < f u n c > ( { " e m p t y " : f u n ( ) : e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) < f u n c > ( { " e m p t y " : f u n ( ) : e n d , " l i n k " : f u n ( ) : e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) < f u n c > (

b

j , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) < f u n c > (

b

j , f u n ( ) : e n d ) < f u n c > ( " n

t

e m p t y " ) " n

t

e m p t y "

Core Surface

desugar

m y

l

i s t = l i s t . [ " l i n k " ] ( 2 , l i s t . [ " e m p t y " ] ) b l

c

k : t e m p M O D R I O U J : : L i s t = m y

l

i s t t e m p M O D R I O U J . [ " _ m a t c h " ] ( { " e m p t y " : f u n ( ) : p r i n t ( " e m p t y " ) e n d , " l i n k " : f u n ( s

m

e t h i n g , _ ) : p r i n t ( " n

t

e m p t y " ) e n d } , f u n ( ) : r a i s e ( " c a s e s : n

c

a s e s m a t c h e d " ) e n d ) e n d m y

l

i s t = [ 2 ] c a s e s ( L i s t ) m y

l

i s t : | e m p t y ( ) = > p r i n t ( " e m p t y " ) | l i n k ( s

m

e t h i n g , _ ) = > p r i n t ( " n

t

e m p t y " ) e n d

SLIDE 58

58

1. Redex semantics engineering tool
2. Racket (racket.org)
3. Pyret (pyret.org)

SLIDE 59

59

Resugaring

The Confection tool

Declarative sugar specification
Language agnostic
Guarantees Emulation and Abstraction

Current/future work

Hygiene!
Better error messages

through resugaring

tinyurl.com/resugar

SLIDE 60

60

SLIDE 61

61

BACKUP SLIDES

SLIDE 62

62

How should this resugar? l e t t = n

t

( t r u e ) i n i f t t h e n t e l s e t r u e

Looks like the desugaring of an ‘or’. But maybe the user wrote it?

SLIDE 63

63

r
r

Core Surface

l e t t = n

t

( t r u e ) i n i f t t h e n t e l s e f a l s e l e t t = f a l s e i n i f t t h e n t e l s e f a l s e i f f a l s e t h e n f a l s e e l s e f a l s e f a l s e n

t

( t r u e )

r

f a l s e f a l s e

r

f a l s e f a l s e

desugar resugar resugar resugar

SLIDE 64

64

s1

Surface

c1 c2 c3 s2

Core

How do we make this transparent?

…

val

…

val

desugar resugar resugar

SLIDE 65

65

Reconstruct the (core) program as source at each evaluation step (along with its tags). Either instrument the compiler

r do a pre-compilation step

CPS/ANF makes this easier;

r just statefully keep track of the stack

SLIDE 66

66

Max2 Max2

Core

desugar resugar

M a x ( [ ] )

>

R a i s e ( “ e m p t y l i s t ” ) ; M a x ( x s )

>

M a x A c c ( x s ,

i

n f i n i t y ) ; M a x ( [

i

n f i n i t y ] ) M a x A c c ( [

i

n f i n i t y ] ,

i

n f i n i t y ) M a x A c c ( [ ] ,

i

n f i n i t y ) Surface M a x ( [ ] )

SLIDE 67

67

Related Work

J. Hennessy. Symbolic debugging of optimized code.

Transactions on Programming Languages and Systems, 4(3), 1982.

J. Clements, M. Flatt, and M. Felleisen. Modeling an

algebraic stepper. In European Symposium on Programming Languages and Systems, 2001.

R. Perera, U. A. Acar, J. Cheney, and P

. B. Levy. Functional programs that explain their work. In International Conference on Functional Programming, 2012

A. V. Deursen, P