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Apparently, the convention (at least starting from 2018) is to make the keywords and block names to be in lowercase as stated from one of the following discussions at https://orgmode.org/list/87tuuw3n15.fsf@nicolasgoaziou.fr/. The files was updated with a one liner of shell. However, this is Emacs and org-mode does have an API to let you do stuff in your config and interact with the documents internally so it is not an elegant solution in any way.
82 lines
3.0 KiB
Org Mode
82 lines
3.0 KiB
Org Mode
#+title: The overview of a programming environment
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#+author: "Gabriel Arazas"
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#+email: "foo.dogsquared@gmail.com"
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#+date: "2020-06-09 06:21:37 +08:00"
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#+date_modified: "2020-09-09 05:18:47 +08:00"
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#+language: en
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#+options: toc:t
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#+property: header-args :exports both
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#+tags: compsci
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The study of [[file:2020-06-03-15-21-42.org][Computational processes]] start with the study of a programming environment.
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The programming environment is mostly a given in programming but let's inspect and state some things (and some are obvious) about it.
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* The elements of programming
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A programming language enables you to make the following:
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- Expressions ranging from a primitive value to a complex type.
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- A way to combine simple expressions into complex ones.
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- A way to abstract procedures into higher-level processes.
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* Expressions
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Expressions may be of a primitive value (e.g., ~265~, ~-1.0~, ~'string~) or *combinations* which are composed of operators and expressions (e.g., ~(+ 2 6)~, ~(* 6 3)~).
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An expression can also hold expressions referred to as a subexpression (e.g., ~(+ (* 5 12) (- 54 6) 9)~).
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[fn:: In Lisp, it uses the *prefix notation* which places the operator in the leftmost of the expression.
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It has the advantage of removing ambiguity for indicating its arguments (e.g., ~5 + 67 + (6 * 4)~ vs ~(+ 5 67 (* 6 4))~).]
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* Namespacing and function composition
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A programming environment should have a way to refer to computational objects.
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These often comes in the form of names with each referring to a value (e.g., ~(define x 10)~).
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A programming language should also provide the way to combine simple procedures to compound procedures (e.g., ~(define (square x) (* x x))~) which can be referred to by name (e.g., ~(square 10)~ evaluates to ~100~).
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With that said, we can then combine compound procedures to create a procedure of higher level (e.g., ~(define (sum-of-squares x y) (+ (square x) (square y)))~).
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* Conditionals
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With expressions, environment, and function composition, we can create simple programs.
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However, we cannot create functions that may test for the value (e.g., [[wikipedia:Piecewise functions][piecewise functions]]).
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For this, a way to conditionally evaluate a value is a must for a programming language.
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Here's an example function of getting the absolute value of a number.
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#+begin_src scheme :results silent
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(define (abs x)
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(cond
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((< x 0) (- x))
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(else x)))
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#+end_src
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* Evaluation model
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Each interpreter implements a different way to evaluate expressions.
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One of the simplest evaluation model is the *substitution model* [fn:: It is also used as a introductory tool for learning interpreters even though this is not how interpreters really work.].
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The substitution model works by knowing the meaning of each value and substituting the value with its equivalent.
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[fn:: The substitution model can also evaluate in *applicative* or *normal* order.]
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* Related resources
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- [[https://mitpress.mit.edu/sites/default/files/sicp/full-text/book/book-Z-H-10.html][/Structure and interpretation of computer programs/, chapter 1]]
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