Common Errors

This page lists common errors you may encounter when writing Luma programs and how to fix them.

Compilation errors

“declared and not used”

app.luma:5:2: declared and not used: x

Cause: You declared a variable but never used it. Luma (via Go) does not allow unused variables.

Fix: Either use the variable or remove the declaration.

“undefined: name”

app.luma:3:5: undefined: username

Cause: You’re referencing a variable or function that hasn’t been declared.

Fix: Check for typos in the name, or make sure the variable is declared before it’s used.

“unknown field in struct literal”

unknown field "email" in struct literal Person; valid fields are: name, age

Cause: You’re trying to set a field that doesn’t exist on the struct.

Fix: Check the struct definition for the correct field names.

“duplicate field in struct literal”

duplicate field "name" in struct literal Person

Cause: You’re setting the same field twice in a struct constructor.

Fix: Remove the duplicate field assignment.

Import errors

“no exported symbols found”

import "helpers": no exported symbols found. Make sure declarations are marked `pub`

Cause: The imported file exists but has no pub fn or pub declarations.

Fix: Mark the functions you want to export with pub:

// helpers.luma
pub fn greet(name: str) -> str {
    return "Hello, ${name}"
}

“module has no namespace-exposable exports”

Cause: The imported module was found but contains no public functions or variables that can be accessed through a namespace.

Fix: Add pub to the functions and variables you want to export.

Impl errors

“impl method must have ‘self’ as first param”

Cause: Methods inside an impl block must take self as their first parameter.

Fix:

impl Person {
    fn greet(self) -> str {
        return "Hi, I'm ${self.name}"
    }
}

Walk errors

“walk requires one or two loop variables”

Cause: You passed zero or more than two parameters to .walk().

Fix: Use one parameter (value only) or two parameters (index and value):

// One parameter
items.walk(item) -> print(item)

// Two parameters
items.walk(i, item) -> print("${i}: ${item}")

“set walk requires exactly one loop variable”

Cause: Sets don’t have indices, so .walk() on a set only accepts one parameter.

Fix:

names: {str} = {"Alice", "Bob"}
names.walk(name) -> print(name)

“file.walk() requires exactly one parameter”

Cause: File walk iterates over lines and only accepts one parameter (the line variable).

Fix:

file("data.txt").walk(line) -> {
    print(line)
}

Type errors

“cannot use X as type Y”

Cause: You’re assigning a value of the wrong type to a variable.

Fix: Make sure the types match. Use type conversion if needed:

s: str = "42"
n: int = s.to_int(0)    // convert string to int with default

Mixing int and float

If you get unexpected results from arithmetic, remember that int / int produces an int (truncated). Use float when you need decimal results:

result: float = 7 / 2       // 3.5 (coerced because result is float)

Runtime errors

Nil pointer dereference

Cause: You used an optional value that was nil without checking first.

Fix: Always check optionals before using them:

x: ?int = "abc".to_int()

if x != nil {
    print(x)
}

Or use a default value:

x: int = "abc".to_int(0)    // defaults to 0

File not found

Cause: You tried to read a file that doesn’t exist with a non-optional return type.

Fix: Either check existence first or use an optional return:

// Check first
if file("data.txt").exists() {
    content: str = file("data.txt").read()
}

// Or use optional
content: ?str = file("data.txt").read()