Error Messages Guide

This guide covers the most common errors you'll encounter when compiling RedScript. For each error you'll find the cause, a code example that triggers it, and how to fix it.

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TypeError: Type Mismatch (int vs fixed/double)

Category: TypeError

Cause

RedScript has no implicit numeric coercions. Mixing int and fixed (or int and double) in arithmetic or assignment without an explicit cast is a compile-time error.

Triggered by

let score: int = 100;
let bonus: fixed = 1.5;

// ❌ TypeError: Type mismatch: cannot implicitly convert fixed to int
//    (use an explicit cast: 'as int')
let total: int = score + bonus;

fn give_xp(amount: int) { /* ... */ }

let multiplied: fixed = 2.5;
// ❌ TypeError: Argument 1 of 'give_xp' expects int, got fixed
give_xp(multiplied);

Fix

Cast explicitly using as:

let score: int = 100;
let bonus: fixed = 1.5;

// ✅ Cast score to fixed, then do fixed arithmetic
let total_fixed: fixed = score as fixed + bonus;
// ✅ If you need an int result, cast back
let total: int = total_fixed as int;

give_xp(multiplied as int);   // ✅ truncates fraction

Cast semantics:

• x as fixed — multiplies by 10000 (int → fixed)
• x as int — divides by 10000, truncating fraction (fixed → int)
• x as double — promotes to IEEE 754 double

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[StringConcat] String Concatenation with +

Category: TypeError (lint warning with tag [StringConcat])

Cause

RedScript does not support the + operator for string concatenation. The + operator is reserved for numeric addition. Attempting to concatenate strings with + produces this error.

Triggered by

let name: string = "Steve";
let greeting: string = "Hello, " + name;
// ❌ [StringConcat] String concatenation with '+' is not supported.
//    Use f-strings instead: f"text{variable}"

let score: int = 42;
let msg: string = "Score: " + score;
// ❌ Same error

Fix

Use an f-string (format string):

let name: string = "Steve";
let greeting = f"Hello, {name}";       // ✅

let score: int = 42;
tell(@s, f"Score: {score}");           // ✅ — pass directly to tell/say/subtitle
actionbar(@a, f"Level: {level}");      // ✅

Note: F-strings can be passed to tell, say, subtitle, title, actionbar, and announce. They cannot be stored in a string variable — they are format_string typed and are consumed at the call site.

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[FloatArithmetic] Float Used in Arithmetic

Category: TypeError (lint warning with tag [FloatArithmetic])

Cause

float is a deprecated type from older versions of RedScript. It is a system-boundary type meant only for reading/writing MC NBT float values — not for arithmetic. Using float in arithmetic expressions generates this warning. The results are undefined.

Triggered by

let x: float = 1.5;
let y: float = 2.0;
let z: float = x * y;
// ⚠ [FloatArithmetic] 'float' is a system boundary type (MC NBT);
//   use 'fixed' for arithmetic. Float arithmetic results are undefined.

fn compute(a: float): float {
    return a * 2.0;
// ⚠ [FloatArithmetic] 'float' is a system boundary type (MC NBT float);
//   use 'fixed' for arithmetic instead.
}

Fix

Replace all uses of float with fixed. Use mulfix() from stdlib/math for multiplication:

import "stdlib/math"

let x: fixed = 1.5;
let y: fixed = 2.0;
let z: fixed = mulfix(x, y);   // ✅ = 3.0

fn compute(a: fixed): fixed {
    return mulfix(a, 2.0);     // ✅
}

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FunctionNotFound / Function Called with Wrong Arguments

Category: TypeError

Cause

Calling a function that hasn't been declared in scope. Usually caused by:

1. Forgetting to import a stdlib module
2. Typo in the function name
3. Calling a function before it's declared (top-level order shouldn't matter, but module library functions require import)

Triggered by

// ❌ mulfix is from stdlib/math — needs an import
let result: fixed = mulfix(1.5, 2.0);
// TypeError: (no explicit "FunctionNotFound" tag, but will fail to compile)

// ❌ Typo
let s: int = sin_Hp(450000);   // should be sin_hp

// ❌ Missing import for math_hp
import "stdlib/math"   // wrong module
let s: int = sin_hp(450000);   // sin_hp is in stdlib/math_hp

Fix

Add the correct import statement at the top of your file:

import "stdlib/math"       // mulfix, divfix, abs_fixed, clamp_fixed, …
import "stdlib/math_hp"    // sin_hp, cos_hp, ln_hp, init_trig
import "stdlib/random"     // rand, rand_range
import "stdlib/list"       // list_sort, list_filter, …

let result: fixed = mulfix(1.5, 2.0);   // ✅

Check spelling carefully — function names are case-sensitive.

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Wrong Number of Arguments

Category: TypeError

Cause

Calling a function with too many or too few arguments.

Triggered by

fn greet(name: string, title: string) {
    say(f"Hello, {title} {name}!");
}

greet("Steve");
// ❌ TypeError: Function 'greet' expects 2 arguments, got 1

Fix

greet("Steve", "Sir");   // ✅

For functions with default parameters, you can omit trailing arguments:

fn greet(name: string, title: string = "Player") {
    say(f"Hello, {title} {name}!");
}

greet("Steve");           // ✅ title defaults to "Player"
greet("Steve", "Sir");    // ✅ explicit title

---

Return Type Mismatch

Category: TypeError

Cause

The value returned from a function doesn't match the declared return type.

Triggered by

fn get_ratio(): fixed {
    return 42;
    // ❌ Return type mismatch: cannot implicitly convert int to fixed
    //    (use an explicit cast: 'as fixed')
}

Fix

fn get_ratio(): fixed {
    return 42 as fixed;   // ✅
}

---

Assign to Const

Category: TypeError

Cause

Attempting to reassign a value to a const variable.

Triggered by

const MAX_PLAYERS: int = 8;
MAX_PLAYERS = 16;
// ❌ TypeError: Cannot assign to const 'MAX_PLAYERS'

Fix

Use let if the variable needs to be mutable:

let max_players: int = 8;
max_players = 16;   // ✅

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setTimeout / setInterval Inside a Loop or Conditional

Category: TypeError

Cause

setTimeout and setInterval allocate a scoreboard slot at compile time. They cannot be called inside a loop or conditional body where the allocation would be ambiguous.

Triggered by

fn setup_timers(count: int) {
    for i in 0..count {
        setTimeout(20, fn() { say("tick"); });
        // ❌ setTimeout() cannot be called inside a loop.
        //    Declare timers at the top level.
    }
}

Fix

Move timer declarations to the top level of a function (outside any loop or conditional):

fn setup_timers() {
    setTimeout(20, fn() { say("tick"); });   // ✅
}

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Quick Reference

Error tag	Meaning	Quick fix
TypeError: cannot implicitly convert X to Y	Mixed numeric types	Add as Y cast
[StringConcat]	Used + on strings	Use f"...{var}..." f-string
[FloatArithmetic]	Used deprecated float in math	Change to fixed, use mulfix()
Function 'X' expects N arguments, got M	Wrong arg count	Check function signature
Return type mismatch	Return type doesn't match declaration	Cast return value
Cannot assign to const	Reassigned a const	Use let instead
setTimeout() cannot be called inside a loop	Timer in loop/conditional	Move to top-level