Tel-Aviv university 05-28, 2004

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The e Language

• Tel-Aviv university 05-28, 2004

Meir Ovadia
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Agenda

• The e language
• Syntax and Semantic
• Examples of usage
• Comparing to AspectJ
• e as predicate classes language
• Conclusions

Tel-Aviv University
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About us

• We are Verisity (www.verisity.com)
• We deal in functional verification
• Verification of chips, boards, boxes
• DUT simulated e.g. in VHDL / Verilog
• Main product Specman Elite
• Language e

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Verifying a DUT using Specman
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The e language

• A lexically-scoped, single-inheritance,
  general-purpose AO language
• constructs
• Constraints
• Coverage definitions
• Parallelism
• Temporal constructs
• Bit-access
• sequences

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The e language

• Compilation and interpretation
• No pre-processor
• Aspects (modules) can loaded/compiled on top of
  existing environment

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Syntax struct declaration
// env.e struct packet i int j
int keep i lt j 1 keep j in 1..5 foo()
is out(Im in foo)
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Syntax Struct extension

• // special.e
• import env.e
• extend packet keep j 3
• foo() is also
• print j

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Syntax Inheritance

• // cell.e
• import env.e
• struct cell like packet
• header list of bit keep soft header.size()
  56
• foo() is first
• header0..31 pack(NULL,j)

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Semantic structs layers

• Each struct declaration or extension called
  struct layer
• Each layer encapsulate behavior (and data)
• Collections of layers (from different struct)
  called aspect.
• The struct layers order is the load order

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Aspect example
// display.e import env.e extend dog
display() is extend poodle display()
is only extend cat display() is
extend snake display() is extend
packet display() is
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Semantic Methods layers

• Each method declaration or extension called
  method layer
• Method can declared by
• undefined (i.e. run time error)
• empty
• is
• Method can extended by
• is also (add new layer after existing behavior)
• is first (add new layer before existing
  behavior)
• is only (new layer override existing behavior)

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Method layers example
struct A do() int is empty do() int
is also out(1) return 0 struct B like A
do() int is only out(3) return 10 struct
C like A do() int is first out(4) extend
A do() int is also out(5) extend B
do() int is also out(6) result a.do()
1,5 (result 0) result b.do() 3,5,6
(result 10) result c.do() 4,1,5 (result
0) extend dog display() is
extend poodle display() is only
extend cat display() is extend snake
display() is extend packet display() is

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Encapsulation in e

• Packages (like in Java)
• Types namespace (like in Java)
• Access control
• Public for all packages
• Private to one package
• Private to one struct (i.e. for all layers
  including descendants layers)
• Private to only one layer
• Friend

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Monitoring

• Logging
• lt
• // logging.e
• import env.e
• extend packet
• foo() is also log()
• doo() is also log()
• goo() is also log()
• gt

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Monitoring (cont.)

• Tracing Specman has trace package build in.
• Profiling e has profiler as part of the
  language. (same as other languages has garbage
  collector).
• Code style use the reflection.

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Linting

• Forcing access to fields only via setters and
  getters
• lt
• // point.e
• import env.e
• extend Point
• layer private x int
• layer private y int
• public setX(val int) is x val
• public setY(val int) is y val
• public getX() int is return x
• public getY() int is return y
• gt

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Aspect encapsulation
// eat.e package eating import env.e extend
Animal eat() is undefined extend Mammal
eat() is only extend Dog eat() is also
extend Fowl eat() is only extend
LoveBird eat() is first
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Patches

• Very easy to send a patch to customers
• lt
• extend my_struct
• foo() is only .
• div(i int j int) is first
• if (j 0) error()
• gt

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Testing

• Each test extend the core environment and modify
  it.

lt //Test2.e extend packet keep kind
error send() is only
check() is only gt
lt //Test1.e extend packet keep
data.size() 50 send() is first
data0 data5 check() is
also gt
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Predicate Classes

• Similar to Craig Chambers Predicate Class
• Useful for specifying multiple, almost-orthogonal
  dimensions.
• Metamorphism
• No need to explicitly enumerate all combinations
• Security and factory.

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Predicate classes Example
type color_t red, green, blue type size_t
big, small extend packet color color_t
size size_t when red packet keep
data.size() 40 when green small packet
show() is also when green packet foo()
is when big packet . when red
big packet
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Local optimization
// opt.e import env.e extend Algorithm
keep cond gt kind opt extend opt
Algorithm calc() is only
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Disadvantage of e

• Private language (private BNF)
• No abstract classes
• Small users community (comparing to C)
• Java has some advantages on e. (like Jbuilder or
  databases packages)

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Advantage of e

• Powerful AOP but yet no new concepts
• Easy to manage
• Easy to collect struct layers
• Easy to collect method layer (by declare order or
  run time order)
• Easy to debug (break on layer or on all layers)
• Aspect can loaded on top of compiled env
• Good performance (method layer equal to method
  call)
• Many commercial tools use e (as AO language)
• Not break the OOP encapsulation

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Conclusion

• AO is not a keyword to mess oriented
• AOP can not replace good modeling
• Someday in the future someone will write NEW open
  source AOP language and it will looks like e
  (same ideas).
• We need do declare how to model problems using
  AOP?

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Other issues related to e

• The e parser (backtracking)
• The temporal language in e
• The constraint solver in e
• The define as and define as computed
• Ports to any simulator
• The eCel
• Bit slice algorithms

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Thank you
Tel-Aviv University