Monday, 2 March 2015

CSE341: Programming Languages, Winter 2013

CSE341: Programming Languages, Winter 2013

Course Information

Course Materials

Material in the future naturally subject to change in terms of coverage or schedule
  1. Unit 1: ML Functions, Tuples, Lists, and More    Reading Notes    Videos
  2.   L1. Jan 7-9: Course Mechanics, ML Variable Bindings   slides: pptx   pdf   pdf6up   code: sml
  3.   L2. Jan 9: Functions, Pairs, Lists   slides: pptx   pdf   pdf6up   code: sml
  4.   S1. Jan 10: Emacs, SML Mode, Shadowing, Error Messages   slides: pdf   pdf4up   code: errors.sml   solutions.sml
  5.   L3. Jan 11: Local Bindings, Options, Benefits of No Mutation   slides: pptx   pdf   pdf6up   code: sml
  7. Unit 2: Datatypes, Pattern Matching, Tail Recursion, and More    Reading Notes    Videos
  8.   L4. Jan 14: Records, Datatypes, Case Expressions   slides: pptx   pdf   pdf6up   code: sml
  9.   L5. Jan 16: More Datatypes and Pattern Matching   slides: pptx   pdf   pdf6up   code: sml
  10.   S2. Jan 17: Type Synonyms, Polymorphism, & More   slides:   pptx   pdf   code:   synonyms.sml   generics.sml  equality.sml   fun_patterns.sml
  11.   L6. Jan 18: Nested Pattern-Matching, Exceptions, Tail Recursion   slides: pptx   pdf   pdf6up   code: sml 
    Tail recursion moved to Jan 23 after the Jan 21 holiday
  13. Unit 3: First-Class Functions and Closures    Reading Notes    Videos
  14.   L7. Jan 23: First-Class Functions   slides: pptx   pdf   pdf6up   code: sml
  15.   S3. Jan 24: Standard-Library Docs, Unnecessary Function Wrapping, Map, & More   slides: pdf   pdf4up   code:sec3.sml   higher-order.sml
  16.   L8. Jan 25: Lexical Scope and Function Closures   slides: pptx   pdf   pdf6up   code: sml
  17.   L9. Jan 28: Function-Closure Idioms   slides: pptx   pdf   pdf6up   code: sml
  19. Unit 4: ML Modules, Type Inference, Equivalence, & More    Reading Notes    Videos
  20.   L10. Jan 30: ML Modules   slides: pptx   pdf   pdf6up   code: sml
  21.   S4. Jan 31: Mutual Recursion, More Currying, More Modules   slides:   pptx   pdf   code:   all_pairs.sml   bank.sml  mutual_rec.sml
  22.   L11. Feb 1: Type Inference   slides: pptx   pdf   pdf6up   code: sml
  23.   L12. Feb 4: Equivalence   slides: pptx   pdf   pdf6up
  25. Course-Motivation Interlude, Feb 4-6  slides  pdf  pdf6up   Videos
  27. Unit 5: Racket, Delaying Evaluation, Memoization, Macros    Reading Notes    Videos
  28.   L13. Feb 6-11: Racket Introduction   slides: pptx   pdf   pdf6up   code: rkt
  29.   S5. Feb 7 <Midterm Review for Midterm on Feb 8>
  30.   L14. Feb 13: Thunks, Laziness, Streams, Memoization   slides: pptx   pdf   pdf6up   code: rkt
    Some of the material in L14 is covered in S6 instead
  31.   S6. Feb 14: More streams, memoization, etc.   slides: pdf   pdf6up   code: sec6.rkt   streams.rkt
  32.   L15. Feb 15: Macros   slides: pptx   pdf   pdf6up   code: rkt
  34. Unit 6: Structs, Implementing Languages, Static vs. Dynamic Typing    Reading Notes    Videos
  35.   L16. Feb 15-20: Datatype-Style Programming With Lists or Structs   slides: pptx   pdf   pdf6up   code: rkt   sml
  36.   L17. Feb 20-22: Implementing Languages Including Closures   slides: pptx   pdf   pdf6up   code: rkt
    Some of the material in L17 is covered in S7 instead
  37.   S7. Legal ASTs, Macros as Functions, and More   slides: pdf
  38.   L18. Feb 22-25: Static vs. Dynamic Typing   slides: pptx   pdf   pdf6up   code: rkt   sml
  40. Unit 7: Ruby, Object-Oriented Programming, Subclassing    Reading Notes    Videos
  41.   L19. Feb 27: Introduction to Ruby and OOP   slides: pptx   pdf   pdf6up   code: lec19_silly.rb   lec19_example.rb
  42.   S8. Ruby arrays, hashes, ranges, blocks, and more slides   (See also material posted with L20.)
    Some of the material in L20 is covered in S8 instead
  43.   L20. Mar 1-4: Arrays & Such, Blocks & Procs, Inheritance & Overriding   slides: pptx   pdf   pdf6up   code: rb
  44.   L21. Mar 4-6: Dynamic Dispatch Precisely, and Manually in Racket   slides: pptx   pdf   pdf6up   code: rb   sml   rkt
  46. Unit 8: Program Decomposition, Mixins, Subtyping, and More    Reading Notes    Videos
  47.   L22. Mar 6-8: OOP vs. Functional Decomposition; Adding Operators & Variants; Double-Dispatch 
       slides: pptx   pdf   pdf6up   code stage A:   sml   rb   java   code stage B:   sml   rb   java   code stage C:   sml   rb   java
  48.   S9. Mar 7: Double-Dispatch, Expression Problem, Mixins, and Visitors   slides: pdf   pdf6up   code: janken.rb  janken.sml   helpers.sml   mixins.rb   visitor.rb   visitor.sml
  49.   L23. Mar 8: Multiple Inheritance, Mixins, Interfaces, Abstract Methods   slides: pptx   pdf   pdf6up   code: rb
  50.   L24. Mar 11-13: Subtyping   slides: pptx   pdf   pdf6up
  51.   L25. Mar 13: Subtyping for OOP; Comparing/Combining Generics and Subtyping   slides: pptx   pdf   pdf6up
  52.   S10. Mar 14: Review, Especially Subtyping   slides: pdf   counter-examples
  54. L26. Mar 15: Course Victory Lap   slides: pptx   pdf   pdf6up

Cross Origin Resource Sharing (CORS) Blocked for Cloudfront in Rails

Using a CDN like AWS Cloudfront helps speed up delivery of static assets to your visitors and reduce the load on your servers. Setting up Cloudfront for your Rails apps is very simple, thanks to gems like asset_sync that work nicely with Rails’ asset pipeline compilation process and S3.
One issue can however be tricky to solve sometimes: CORS blocks.

What is happening?

If your assets are served by a CDN like Cloudfront, they can be served from a domain while your app is served on This triggers CORS blocking in browsers to stop malicious websites fetching nasty resources while browsing a seemingly nice website.
The most common type of this issue is with fonts when you get something like this:
Font from origin '' has been blocked from loading by Cross-Origin Resource Sharing policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin '' is therefore not allowed access.  

How to fix it?

When it comes to AWS Cloudfront, the most commonly suggested method is to allow CORS origins on the Cloudfront side. This method involves writing XML configuration code for AWS and uploading it on the S3 side.

There is a better and easier way!

I personally prefer using my DNS subdomains to solve this problem. If my CDN is instead of then browsers are not going to freakout and block them as cross domain security problems.
To point your subdomain to your AWS Cloudfront domain go to AWS Cloudfront control panel, select your Cloudfront distribution and enter your CDN subdomain into the Alternate Domain Names (CNAMEs) field. Something like will do.
Now you can go to your DNS provider (like AWS Route 53) and create a CNAME pointing to
You can test your new CDN domain by making sure assets served from it are coming from Cloudfront.
curl -I  
should return something like this
HTTP/1.1 200 OK  
Content-Type: image/png  
Content-Length: 10414  
Connection: keep-alive  
Date: Mon, 22 Sep 2014 10:06:41 GMT  
Last-Modified: Sun, 06 Jan 2013 16:37:19 GMT  
ETag: "1c4bef3752c306b9c14a05b4a19d7d79"  
Accept-Ranges: bytes  
Server: AmazonS3  
Age: 1599  
X-Cache: Hit from cloudfront  
Via: 1.1 (CloudFront)  
X-Amz-Cf-Id: sEbH-vV6deQra_YQa144RxtwhuJaWSrq-tpdiFxWdUbDbR2DnhoIrQ== 

AssetSync disabled in development