Compile errors, explained

Every error is file:line: message, shown on the in-engine error screen. Fix the file and save — the game hot-reloads. The catalogue, A–Z by cause:

Message (pattern)	Meaning	Fix
expected str, got str? (any types)	using an optional (or wrong type) where a plain value is needed	unwrap with ?? or narrow with if x != nil { }
if condition must be bool (wick has no truthiness)	if x on a number/string	write the comparison: if x > 0, if s != ""
unknown variable 'x' — wick has no implicit globals; use let	assigned a name never declared (often a typo)	let x = ..., or fix the spelling
unknown variable 'x' (declare it with let)	read of an undeclared name	same
'+' needs num+num or str+str (use str(x))	mixed-type +	convert explicitly: "n=" + str(n)
f() argument 3: expected num, got str	typed call mismatch (engine or your fn)	check the API table
f() needs at least N arguments / takes N arguments	arity mismatch	see signature
unknown function 'f' (wick requires declare-before-use)	called above its definition	move the fn up
can't infer a type from nil; annotate: let x: str? = nil	bare nil initializer	add the annotation
empty [] needs a type: let xs: list<num> = []	untyped empty literal	annotate the let
list elements must share one type	[1, "a"]	homogeneous lists only
comparing non-optional to nil	x != nil on a plain type	it can never be nil; delete the check
'??' left side must be an optional	a ?? b where a can't be nil	delete the ??
'x' already declared in this scope	duplicate let	assign instead, or rename
parenthesize this condition: (a != b) and ...	narrowing pattern mixed with logic	add parentheses
break outside a loop / continue outside a loop
fn declarations can't nest	fn inside fn	top level only (v0.1)
return outside a function / void function can't return a value / this function must return T	return/type mismatch	align with the declared return type
map keys must be str literals	computed keys in a literal	build with m[k] = v
container elements must be num, bool, or str	nested containers	see limits

Runtime errors

Static types can't remove these; they stop the frame and show on the error screen with a line number:

Message	Cause
list index N out of range (len M)	out-of-bounds xs[i] (read or write)
check failed: <msg>	your own check() assertion
load_texture/mesh/sound failed: <path>	missing or bad asset