Delimited continuations manipulate the control flow of programs. Similar to control structures like conditionals or loops they allow to deviate from a sequential flow of control.
We use exception handling as another example for control flow manipulation and later show how to implement it using delimited continuations. Finally, we show that nondeterminism can also be expressed using delimited continuations.
| s x y z = x z (y z) | |
| k x y = x | |
| i = s k k | |
| c = s (s (k (s (k s) k)) s) (k k) | |
| b = s (k s) k | |
| hello = | |
| s(s(k s)(s(k k)(s(k s)(s(k(s(k s)))(s(s(k s)(s(k k)(s(k b)i)))(k(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s | |
| b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(c k)))))))))))))))))))))))))))))))))))))))))) | |
| )))))))))))))))))))))))))))(s(s(k s)(s(k k)(s(k s)(s(k(s(k s)))(s(s(k s)(s(k k)(s(k b)i)))(k(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s b(s |
| CFLAGS = -std=c99 -Wall | |
| main : main.o | |
| .PHONY : test clean | |
| test : main | |
| ./$^ "*regex*" "*vtable*" < main.c | |
| clean : |
| #include <stdio.h> | |
| #define PRINT(...) CAT(CT(__VA_ARGS__))(__VA_ARGS__) | |
| #define CAT(N) DOG(N) | |
| #define DOG(N) PRINT ## N | |
| /* max supported args is 5 for now */ | |
| #define CT(...) VALS(__VA_ARGS__, 5, 4, 3, 2, 1) | |
| #define VALS(N1, N2, N3, N4, N5, N, ...) N |
What is strict aliasing? First we will describe what is aliasing and then we can learn what being strict about it means.
In C and C++ aliasing has to do with what expression types we are allowed to access stored values through. In both C and C++ the standard specifies which expression types are allowed to alias which types. The compiler and optimizer are allowed to assume we follow the aliasing rules strictly, hence the term strict aliasing rule. If we attempt to access a value using a type not allowed it is classified as undefined behavior(UB). Once we have undefined behavior all bets are off, the results of our program are no longer reliable.
Unfortunately with strict aliasing violations, we will often obtain the results we expect, leaving the possibility the a future version of a compiler with a new optimization will break code we th
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| {-# language OverloadedStrings, UnicodeSyntax, LambdaCase, | |
| ViewPatterns, NoMonomorphismRestriction #-} | |
| {-# options_ghc -fwarn-incomplete-patterns #-} | |
| {- Minimal bidirectional dependent type checker with type-in-type. Related to Coquand's | |
| algorithm. #-} | |
| import Prelude hiding (all) |
Here's a list of mildly interesting things about the C language that I learned mostly by consuming Clang's ASTs. Although surprises are getting sparser, I might continue to update this document over time.
There are many more mildly interesting features of C++, but the language is literally known for being weird, whereas C is usually considered smaller and simpler, so this is (almost) only about C.
struct foo {
struct bar {
int x;