Strings and F-Strings

Desi provides powerful string handling with f-string interpolation.

String Basics

let name: str = "Desi"
let greeting: str = "Hello, Desi"
let multiline: str = """
    Multi-line
    string literal
"""

# Concatenation
let full: str = "Hello" + " " + "World"

---

F-Strings (Interpolation)

F-strings let you embed expressions directly in strings:

let name: str = "Alice"
let age: int = 30

print(f"Hello, {name}!")          # Hello, Alice!
print(f"{name} is {age} years old")  # Alice is 30 years old
print(f"Sum: {1 + 2 + 3}")        # Sum: 6

Variable Interpolation

let x: int = 42
let msg: str = f"Value is {x}"

Expression Interpolation

let a: int = 10
let b: int = 20
print(f"Sum: {a + b}")      # Sum: 30
print(f"Product: {a * b}")  # Product: 200

Function Calls

def greet(name: str) -> str:
    return f"Hello, {name}!"

let who = "Bob"
print(f"Message: {greet(who)}")

Struct Fields

struct Point:
    x: int
    y: int

def main() -> int:
    let p: Point = Point(x=5, y=10)
    print(f"Point at ({p.x}, {p.y})")
    return 0

---

Custom Display

Define how your types appear in f-strings:

struct Point:
    x: int
    y: int

impl Display for Point:
    def to_str() -> str:
        return f"({self.x}, {self.y})"

def main() -> int:
    let p: Point = Point(x=5, y=10)
    print(f"Point is {p}")  # Point is (5, 10)
    return 0

---

Format Specifiers

Control how values are formatted using Python-style specifiers:

let pi = 3.14159265
let count = 42

# Float precision
print(f"Pi: {pi:.2f}")      # Pi: 3.14

# Zero-padded integers
print(f"Count: {count:05d}")  # Count: 00042

# Hex formatting
print(f"Hex: {count:x}")    # Hex: 2a
print(f"HEX: {count:X}")    # HEX: 2A

# Width (right-aligned)
print(f"Width: {count:10d}")  # Width:         42

Supported Specifiers

Spec	Description	Example
.Nf	Float with N decimal places	{pi:.2f} → 3.14
Nd	Integer width	{x:5d} → 42
0Nd	Zero-padded integer	{x:05d} → 00042
x	Lowercase hex	{42:x} → 2a
X	Uppercase hex	{42:X} → 2A
o	Octal	{42:o} → 52
#x	Hex with prefix	{42:#x} → 0x2a

---

Escaping Braces

Use double braces for literal { or }:

print(f"Use {{braces}} like this")
# Output: Use {braces} like this

---

String Methods

let s: str = "hello world"

# Common operations
let length: int = len(s)        # 11

split()

Split a string by a delimiter, returning a list of strings:

let csv = "apple,banana,cherry"
let parts = csv.split(",")      # ["apple", "banana", "cherry"]

for item: str in parts:
    print(item)

join()

Join a list of strings with a delimiter:

let words = ["apple", "banana", "cherry"]
let joined = words.join(", ")   # "apple, banana, cherry"
print(joined)

replace()

Replace all occurrences of a substring:

let original = "Hello World"
let result = original.replace("World", "Desi")  # "Hello Desi"
print(result)

---

Quick Reference

Syntax	Description
"text"	String literal
f"Hello, {name}!"	F-string interpolation
"{{" / "}}"	Escaped braces
len(s)	String length
s + t	Concatenation