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Chapter 2: Language Basics

This chapter explores the building blocks of ShellLite: storing data, using different types of information, and talking to the user.

1. Variables

Variables are like labeled boxes where you can store information. You create one simply by giving it a name and using = to assign a value.

name = "Alice"
age = 30
is_happy = yes

You don't need to tell ShellLite what "type" of data it is; it figures it out automatically (dynamic typing).

Variable Naming Rules

  • Must start with a letter or underscore (_)
  • Can contain letters, numbers, and underscores
  • Case-sensitive (Name and name are different)
  • Cannot be a reserved keyword

Constants

Sometimes you want a value that never changes. Use const for this. By convention, we often use ALL CAPS for constants to distinguish them from regular variables.

const PI = 3.14159
const MAX_USERS = 100
const APP_NAME = "ShellLite v0.05"

Note: If you try to change a const later in your code, ShellLite will throw an error.

2. Data Types

ShellLite is dynamically typed, meaning variables can hold any type of value. Here are the core types:

Type Description Example
Number Integers and floating-point numbers 42, 3.14, -10
String Text enclosed in quotes "Hello", 'World'
Boolean Logical yes/no values yes, no, true, false
List Ordered collection of items [1, 2, 3]
Dictionary Key-value pairs {"name": "Alice"}
Function Callable code blocks fn x => x * 2
Object Instance of a class/structure new Car
None/Null Represents absence of value (empty result)

Numbers

Integers (whole numbers) and Floats (decimals).

count = 10
price = 19.99
negative = -5

Arithmetic Operators:

Operator Description Example
+ Addition 5 + 3 → 8
- Subtraction 10 - 4 → 6
* Multiplication 3 * 4 → 12
/ Division 15 / 3 → 5
% Modulo (remainder) 17 % 5 → 2

Compound Assignment:

x = 10
x += 5   # x is now 15
x -= 3   # x is now 12
x *= 2   # x is now 24
x /= 4   # x is now 6
x %= 4   # x is now 2

Natural Language Math:

increment x          # x = x + 1
decrement x          # x = x - 1
multiply x by 3      # x = x * 3
divide x by 2        # x = x / 2

Strings (Text)

Text is enclosed in either double quotes " or single quotes '.

greeting = "Hello World"
quote = 'Keep it simple.'

Escape Sequences:

Sequence Meaning
\n Newline
\t Tab
\r Carriage return
\" Double quote
\' Single quote

Combining Strings: You can join strings using +.

full_name = "John" + " " + "Doe"

String Interpolation: You can inject variables directly into strings using {}. This is often cleaner than using +.

name = "Shrey"
score = 100
say "Player {name} has a score of {score}!"

String Methods:

text = "Hello World"
say text.upper()      # "HELLO WORLD"
say text.lower()      # "hello world"
say len(text)         # 11

Booleans (Yes/No)

Instead of true and false, ShellLite uses yes and no (though true/false work too).

active = yes
sleepy = no
is_ready = true

Truthiness and Falsiness: In ShellLite, certain values are considered "falsy" (evaluate to no in conditions):

  • no / false
  • 0
  • Empty string ""
  • Empty list []
  • Empty dictionary {}

Everything else is "truthy" (evaluates to yes).

Logical Operators

Operator Description Example
and Both must be true yes and yes → yes
or At least one must be true yes or no → yes
not Negates the value not yes → no

3. Output (Say)

To display text on the screen, use the say command. You can also use print or show if you prefer.

say "Welcome!"
print "Processing..."
show "Done."

Colored Output

You can make your output pop with colors!

say in red "Error!"
say in green "Success!"
say bold blue "Info"

Supported colors: red, green, blue, yellow, cyan, magenta, white, black

Supported styles: bold

4. Input (Ask)

To get information from the user via the terminal, use the ask command (or input).

# Simple input
name = ask "What is your name? "
say "Hello " + name

# Using the input in logic
age = ask "How old are you? "
if age > 18
    say "Access Granted"

The ask command pauses the program, prints the prompt (if provided), and waits for the user to type something and press Enter.

5. Operator Precedence

Operators are evaluated in the following order (highest to lowest):

  1. Parentheses ()
  2. Unary operators: not, - (negation)
  3. Multiplication, Division, Modulo: *, /, %
  4. Addition, Subtraction: +, -
  5. Comparison: >, <, >=, <=, ==, !=
  6. Logical AND: and
  7. Logical OR: or
# Example
result = 2 + 3 * 4    # result is 14, not 20
result = (2 + 3) * 4  # result is 20

6. Natural Language Enhancements

ShellLite tries to ignore "filler words" to make code read like English. You can use words like the freely.

if the score is more than 10
    say "Win"

In this example, the is completely ignored by the computer - it's just there for you.

Natural Comparison Phrases

Symbol English Phrase
== is, is exactly, equals
!= is not
>= is at least
<= is at most
> is more than, is greater than
< is less than

Next: Control Flow ->