Something New With Ruby

04 Jun 2014

####Lambda Literals

succ = lambda {|x| x+1}
succ = ->(x){ x+1 }
succ = ->x { x+1 }

####Porc Equality

lambda {|x| x+1 } == lambda {|x| x+1 } # false

p = lambda {|x| x+1 }
q = p.dup
p == q #true
p.object_id == q.object_id #false

####Shorthand for string list

%w{word1 word2 etc}

####Warning Mode

irb -w
ruby -w

####Annotation

TODO
FIXME
OPTIMIZE

rake notes

####Hash

Basically use fetch instead of square brackets- it will raise error if it’s nil.

####String

Flexible quoting:

$(string)
%!string!
%{string}

Shovel(«) operator modifies the original string, while += doesn’t

####Symbol

String.to_sym

I/O

$stdout.reopen 'filename' # redirect standard ouput to a file
$stdin.noecho &:gets # runs gets without echoing input to the screen
$stdin.reopen '/dev/tty' # redirect standard output to the terminal

####Questions?

arr = [1,2,3,4] why arr[4..0] == [] but arr[5..0] == nil

what’s with single quotes sometimes interpret escape characters

@about_symbols.rb:34

@about_constants.rb:87

Note: Rails best practice

04 Jun 2014

update_attribute

Watch out for update_attribute, it doesn’t run model validations. But update_attributes does.

#count, #length and #size for ActiveRecord

Use #size
Use #length if you’ll need to load the real records immediately

SICP: Chapter 1. Building Abstractions with Procedures

14 May 2014

###1.1 The Elements of Programming

####1.1.1 Expressions

Prefix notation

####1.1.2 Naming and the Environment

(define [name] [value])

Defines environment(global environment)

####1.1.3 Evaluating Combinations

####1.1.4 Compound Procedures

(define (square x) (* x x))

####1.1.5 The Substitution Model for Procedure Application

Applicative order versus normal order

normal order: fully expand and then reduce(lazy approach?)
applicative order: (eager approach?)

####1.1.6 Conditional Expressions and Predicates

(cond (<p1> <e1>)
      (<p2> <e2>)
      ...
      (<pn> <en>))

or

(cond (<p1> <e1>)
      ...
      (else <en>))

if statement

(if <predicate> <consequent> <alternative>)

logical composition operations:

and
or
not

####1.1.7 Example: Square Roots by Newton’s Method

In mathematics we are usually concerned with declarative (what is) descriptions
In CS we are usually concerned with imperative (how to) descriptions

####1.1.8 Procedures as Black-Box Abstractions

Each procedure accomplishes and identifiable task that can be used as a module in defining other procedures
Block structure: to make procedures local and make proper variables free

###1.2 Procedures and the Processes They Generate

1.2.1 Linear Recursion and Iteration

###Questions

Is normal order vs applicative order same as lazy evaluation vs eager evaluation
Exercise 1.7

Edwin: notes

14 May 2014

####C and M

C(Control) ctrl
M(Meta) command

####Screen navigation

Move forward C-v
Move backward M-v
Clear screen C-l

####Cursor navigation

Previous line C-p
Next line C-n
Backward one character C-b
Forward one character C-f
Backward one word M-b
Forward one word M-f
Line start C-a
Line end C-e
Sentence start M-a
Sentence end M-e
File start M-<
File end M->

####Usually the Rule

Meta commands are for English text
Control commands are for basic textual units

####Repeat command

C-u <times> [command]

####Stopping Edwin

C-g quit what it was doing
C-c C-c cancel a Scheme evaluation

####Deletion

delete the character just before the cursor
C-d delete the next character after the cursor
M-<Delete> kill the word immediately before the cursor
M-d kill the next word after the cursor
C-k kill from the cursor position to end of line
M-k kill to the end of the current sentence

####Yank

Use C-y

C-y get the most recent kill
M-y get the previous kill

####Evaluating Scheme Expressions

get into an evaluation buffer C-x b *scheme*
C-x C-e evaluate the expression(point is after the closing parenthesis)
M-p to access the history
C-x b TUTORIAL

####Undo

C-x u or C-_

####Files

Find a file C-x C-f
Save the file C-x C-s

####Buffers

List buffers C-x C-b
get rid of the buffer list C-x 1
Save all changed buffers C-x s

####eXtend command

C-x Character eXtend. Followed by one character
M-x Named command eXtend. Followed by a long name

####C-x commands

C-x C-f Find file
C-x C-s Save file
C-x C-b List buffers
C-x C-c Quit Emacs
C-x u Undo

####Named eXtended command(“functions”)

M-x replace-string
M-x scheme-mode

####Modes

C-h m documentation on current mode

####Searching

Forward search C-s
Reverse search C-r

####Recursive editing levels

M-x top-level
In doubt?

####Windows

C-x 1 One window

####Getting help

C-h
C-h ?
C-h c brief description
C-h k documentation of the function
C-h f describe a function
C-h a Command Apropos

###Misc

C-u C-v to bring current line up

The end of this semester

13 May 2014

The final turned out to be OK though at some point I really didn’t think that I can get it through.

I started VM in Weenix pretty late. When I look back, it turns out that I only had 18 days to finish it up. It still has some bugs and I have no idea how to pinpoint them. But I’m still happy that I can finally get it done in such a tight schedule. I have never been totally on schedule, and I really know that driven by deadline can be a terrible process management and a lot pressure on me. It’s just who I am that keeps me doing this.

Relating this to some speech I just saw, maybe I should just simply try to do more things in the same time schedule. You’ll just find a way to utilize your potential and get it done.

Luqi Pan