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Tweak slides.

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Justin Hsu 3 years ago
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      website/docs/resources/slides/lecture-langsec.md

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website/docs/resources/slides/lecture-langsec.md

@ -46,7 +46,7 @@ date: November 21, 2018
- Model "essence" of real languages
## 2. Formalize what programs "do"
- Usually: run it on a machine and find out!
- Run it on a machine and find out?
- Not very useful for proofs...
- Formalize behavior mathematically, on paper
- Discard "unimportant" details
@ -115,7 +115,7 @@ date: November 21, 2018
# Operational Semantics
## Programs execute by "stepping"
## Execute by "stepping"
- Start with program
- Imperative: plus variable setting
- In each step, perform update:
@ -137,8 +137,8 @@ date: November 21, 2018
- A type $\tau$ describes a class of programs
- Usually: well-behaved in some way
- Can automatically check if program has type $\tau$
- Type of program depends on types of its pieces
- Scales to large programs
- Type of program depends on types of components
- Analysis scales to large programs
## Example
@ -146,18 +146,18 @@ date: November 21, 2018
- Lightweight
- Checking types is simple, automatic
- Don't need to run program
- Intuitive meaning
- Natural and intuitive
- Can't add a String to a Boolean
- Programmers often think in terms of types
- Identify correct programs
## Weaknesses
- Programmer may need to add some type hints
- Extra annotations in program
- Programmer may need to add annotations
- Extra hints for compiler
- Common for more complex types
- Compiler sometimes rejects correct programs
- Figuring out why can be very frustrating
- May need to write program in more awkward form
- May need to write program in less natural form
## Types can be complex
- Simpler types
@ -170,9 +170,9 @@ date: November 21, 2018
- ...
## Prove: soundness
- "Soundness theorem"
- Relate type system to operational behavior
- If program has a type, it should be well-behaved
- Relate type system to operational behavior
- "Soundness theorem"
- Many possible notions of "well-behaved"
- Don't add Strings to Bools
- Don't mix public and private data

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