1 create project sunshine

Created 星期一 06 二月 2017

minSDK vs targetSDK

The minSDK is the lowest SDK level that your app can run on. You can choose what level of devices to support.

By comparison, the targetSDK is NOT a high pass filter -- it’s used …

2016年的最后几小时, 随便写写关于Scala和OCaml的一些入门体验好了.

今年对FP语言特别感兴趣, 上了两门Scala的公开课(here and here)和一门OCaml的公开课(here), 在博客中写了一系列的笔记, 课后作业也都认真做完了. 斗胆 …

前一段时间写了不少Python的爬虫程序, 为此还看了极客学院上的一些教程, 现在来简单总结一下. 主要介绍用requests + lxml的方式, scrapy的话之前写 …

this week: programming-in-the-large using the module system of OCaml.

1. STRUCTURING SOFTWARE WITH MODULES

in large project: mangage high number of definitions → abstractions built on top of other abstractions.

• layers of abstractions: hide information
• divide program into components
• identifiers organised to avoid naming conflicts

module as namespace

dot-notation: access module …

1. IMPERATIVE FEATURES IN OCAML

functional language:

• immutable data structure
• identifiers instead of variables
• pure functions

but imperative features are useful:

• exceptions to alter control flow
• ops to consume input and output
• mutable data structures
• for and while loop for iterations

2. GETTING AND HANDLING YOUR EXCEPTIONS

• exceptions in ocaml …

1. FUNCTIONAL EXPRESSIONS

syntax for functional expr: function some_identifier -> some_expr
the type of the functional expr is t1 -> t2 where t1 is the type of some_identifier, t2 is type of some_expr

ex.

function x -> x + 1;;  
(function x -> 2*x) 5;; (*annonymous function*)   

the previous way of defining function:

let …

Last week, we only defined flat data structures which are nice to aggregate values but quite limited when you try to structure values.

This week: algebraic datatypes.

1. TAGGED VALUES

⇒ change the return type to a type query_result, which can be either of these:

• an error
• a new database (in …

this week: structure code with types: tuples, records, arrays.

1. USER-DEFINED TYPES

primary use of types: document your code

• use type type_identifier = some_type to define a new type (type_identifier is synonym/abbrevation of some_type)
• type_identifier must start with lowercase letter
• already known types: int, bool, string, char ...
• use : to add …

this week: discuss how to handle events in user-interface — MVC, functional reactive programming.

Lecture 4.1 - Imperative Event Handling: The Observer Pattern

Traditional way of handling events: observer Pattern (MVC). Used when views need to react to change in a model.

MVC: model-view-controller for user interface

• Views can announce themselves …

This week: scala for imperative programming.

Lecture 3.1 - Functions and State

So far: pure functional programming
→ side-effect free: therefore time doesn't matter.
Any rewriting that terminates lead to the same solution. (Churcher-Rosser Th)

Now: mutable states

Stateful objects: objects can have state that change over time. (state is influenced …