Learn to Program

Learn to Program is a Contents page for topics that are related to the art of programming in general.

Description edit

Writing programs is about knowing what you want to do, and finding a way to do it. Reading programs is about understanding what it does, and figuring out what the author wanted it to do. Any author worth their salt is almost certainly also a voracious reader. Make sure to take time to read programs written by others. Lots of them.

There are, of course, many resources out there in the world that teach beginners the art of computer programming. One of the more well-known is The Structure and Interpretation of Computer Programs, but it uses LISP rather than Tcl. Tcl is a fantastic first language for someone interested in getting into computer programming, and this page introduces Tcl obliquely by introducing the general art of programming, using Tcl as a resource to illustrate the concepts.

Primitives edit

At the hardware level, which is the domain of assembly languages, the primitives of a program are values, storage, instructions. One layer of abstraction up, the primitives for data are values, sequences, and mappings, and the primitives for routine are assignment and function. Some languages abstract some primitives away, but internally they are still there somewhere, in some form, composing the higher-level abstractions.

Primitives that exist at higher levels, e.g. classes and objects in object oriented programming, are implemented in terms of the primitives at lower levels.

Here is how the primitives are used in Tcl:

category	primitive	Tcl
data
	value	any string
	sequence	list
	mapping	dict
routine
	function	proc, apply
	assignment	set, variable, etc.

At lower levels, the primitives are, well, more primitive. In assembly languages, for example, storage locations are just storage locations, and the programmer keeps track of how those locations should be operated on. There is no specific syntax for sequences of values, but clearly, they can be created, and in more ways than one. For example, one might manipulate adjacent storage locations to form a sequence that can be iterated efficiently, or one might form a chain of values that are not sitting adjacent to each other by storing a value together with the address of the next value

. In C, which introduces typed values, the elements of a sequence must be of the same type so that storage can be efficiently allocated. Moving to a higher layer of abstraction, the Tcl take on a sequence, the list, discards this constraint, but loses some efficiency in the process.

Each programming language gets its distinct flavour by combining these primitives in novel ways. In Tcl, there is only one type of value, the string. Curiously, in Tcl both lists and dictionaries are just strings that conform to a certain format, so the seqence and mapping primitives only exist as a set of commands that manipulate correctly-formatted values as lists or mappings. JSON, which has become popular lately, provides for the succinct expression of the data primitives.

The use of each primitive affects storage in some way, and one of the primary concerns in writing a quality program is the effective management of that storage. Thus, whatever level of abstraction one is working at, mastery of the storage aspects is critical. Even things that are considered more related to performance, such as the overhead of variable lookups or function calls, are still very much about how storage is managed and used. In Tcl, copy-on-write is one of the key features related to storage, and a good understanding of it has the power to change the way one writes Tcl programs.

Values and side effects edit

Some commands return useful values, some have side effects, and some do both.

The value of puts is invariant. It always returns the empty string, so it's never useful:

set a [puts hello]

Therefore, puts has a side effect, but no useful value.

set has a side effect. It creates a new variable and assigns a value to it. set also returns the value that it assigned to the variable, which can be useful sometimes. To set two variables to the same value, one could write:

set b [set a hello]

Therefore, set has a side effect and also has a useful value.

string length is an example of a command that doesn't have any side effects but does have a useful value. It changes nothing in the world of a Tcl script. It doesn't create or delete any commands or variables, and it doesn't write any data to any channels. However, it returns a value that tells us something we might want to know:

string length hello

The last category is commands that have no side effect and no value. There are none of these!

Computer Architecture edit

byte: :
A real problem: Why real numbers may not work the way you expect them to in a computer program. See also Computers and real numbers.

Fundamental Concepts edit

Automaton
binary representation
Halting Problem
homoiconicity
scope
syntax

Data Types edit

Abstract Data Types
References

Data Structures edit

Data Structures

Logic edit

Combinatory Logic
predicate logic

Functions edit

curry
lambda
Function mapping
composition

Program Structure edit

Control Structures
Procedures
Closures
Continuations
Coroutines
Concurrency
Generators
Iterators
recursion

State edit

Static Variables
Constants

Persistence edit

Calculation edit

Processing edit

distributed computation
multitasking
parsing
serialization
data analysis
signal processing

Design edit

See Program Architecture.

Paradigm edit

dataflow programming: the next step in a program is determined by the output of the previous step
flow-based programming: like dataflow programming, but articulates the connections as channels and the inputs/outputs as messages
functional Programming: program behavior is described as a mathematical function
little language: purpose-built languages for specific problem domains
object orientation: encapsulation of data and functionality into a discrete operational entity with a defined interface
relation orientation: Related terms includeand subject-oriented programming and Aspect Oriented Programming.

Communication edit

ipc
network programming

Memory Management edit

Garbage collection

Technique edit

Code Generation
data is code
declarative programming
multitasking: Getting multiple things done at once.
debugging
domain-specific language
factoring
imperative programming
Literate programming
Logic programming
profiling
testing
Genetic Programming

Methodology edit

Extreme Programming
programming by exception
test-driven development
Zero-Defect Software Development: Not to be taken as meaning "bug-free," Zero-Defect Software Development (ZDSD) is a practice of developing software that is maintained in the highest quality state throughout the entire development process

Security edit

Injection Attack
Secure by design
Tcl is immune to many "format string vulnerabilities"
The Peon's Guide To Secure System Development

The Role of Scripting Languages edit

Why adding Tcl calls to a C/C++ application is a bad idea

Topical Guide edit

artificial intelligence
algorithms
encryption
graphics

More Theory edit

The following pages introduce various computer science topics, but don't yet have any other place to live in this table of contents

Scripted Compiler
theoretical computer science: a forum

The Art edit

The Strange World of Programming: A foray into ideas, wisdom, and general principles of developing programs and the programmer.
Tips for writing quality software
GCR decoding on the fly, Linus Åkesson, 2013-03-31: in which Linus solves a longstanding problem by looking at it from a novel angle, and employing trickter and clever code in a very concise manner

Do's and Dont's edit

Don't copy and paste from a webpage to a terminal: A malicious website might run arbitrary commands on your system.

Exercises edit

Project Euler: A series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve.

Bookshelf: Freely-Available edit

The Architecture of Open Source Applications: Some great essays on designing programs. The essay on The essay on Berkeley DB is one good one.
97 Things Every Programmer Should Know: A collection of short essays by experienced programmers. Light on code examples, and usually not explanatory enough, but serves well as an index of concepts to read up on.
The Value of Values (video), by Rich Hickey, 2012-08-14: A presentation on the role of data and how it's treated in object-oriented and functional approaches.
What Goes Around Comes Around, Michael Stonebraker and Joey Hellerstein: Provides a summary of 35 years of data model proposals, grouped into 9 different eras.

previous : Tcl Quoting

up: Contents

next : Tcl Commands

Category Tutorial

See Also edit