0006-StringInterpolation.md

String Interpolation

String interpolation provides convenient inline expression evaluation within string literals.

Syntax

String interpolation uses ${} syntax:

let name = "Alice"
let age = 30
let message = "Hello ${name}, you are ${age} years old"

Expression Support

Any expression can be interpolated:

let x = 10
let y = 5
print("Sum: ${x + y}")
print("Product: ${x * y}")
print("Complex: ${(x + y) * 2 - 1}")

// Function calls
fn double(n) = n * 2
print("Doubled: ${double(5)}")

// Field access
type Person = { name: string, age: int }
let person = Person { name: "Bob", age: 25 }
print("Person: ${person.name}, age ${person.age}")

Type Handling

Interpolated expressions are automatically converted to strings:

• Primitive types: int, float, bool converted directly
• String types: Inserted as-is
• Result types: Must be pattern-matched before interpolation
• Complex types: Use toString() for explicit conversion

let num = 42
let flag = true
print("Number: ${num}, Flag: ${flag}")

// Result types require unwrapping
let result = 10 + 5
match result {
    Success { value } => print("Result: ${value}")
    Error { message } => print("Error: ${message}")
}

Escaping

Use backslash to escape special characters:

let literal = "Dollar sign: \${not interpolated}"
let newline = "Line 1\nLine 2"
let quote = "He said \"Hello\""
let backslash = "Path: C:\\Users\\Name"

Supported escape sequences:

• \n - Newline
• \t - Tab
• \r - Carriage return
• \\ - Backslash
• \" - Double quote
• \${ - Literal ${ (prevents interpolation)

Implementation

Interpolated strings compile to efficient buffer operations:

1. Allocate a buffer (alloca [1024 x i8])
2. Use sprintf with appropriate format specifiers (%s, %ld, etc.)
3. Return the formatted string for use in expressions