Added more tests

src/build/core/CompileCall.go

@@ -2,6 +2,7 @@ package core
 
 import (
 	"git.akyoto.dev/cli/q/src/build/asm"
+	"git.akyoto.dev/cli/q/src/build/errors"
 	"git.akyoto.dev/cli/q/src/build/expression"
 )
 
@@ -11,9 +12,18 @@ import (
 // After the function call, they must be restored in reverse order.
 func (f *Function) CompileCall(root *expression.Expression) error {
 	funcName := root.Children[0].Token.Text()
+	isSyscall := funcName == "syscall"
+
+	if !isSyscall {
+		_, exists := f.functions[funcName]
+
+		if !exists {
+			return errors.New(&errors.UnknownFunction{Name: funcName}, f.File, root.Children[0].Token.Position)
+		}
+	}
+
 	parameters := root.Children[1:]
 	registers := f.cpu.Input[:len(parameters)]
-	isSyscall := funcName == "syscall"
 
 	if isSyscall {
 		registers = f.cpu.Syscall[:len(parameters)]