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 …

1. BASIC DATA TYPES: int, bool

Rich type system and polymorphism in ocaml. Types are infered not declared.

Basic types: int, bool, float, string, char, ...

int

value: $-2^{62}$ ~ $2^{62}-1$ on 64-bit machines.
ops: +, -, *, /, mod (reminder: / is integer division)

# 3+2*4-1;; 
- : int = 10 
# 5/2;; 
- : int …