Simplified file structure

src/core/Define.go

@@ -0,0 +1,31 @@
+package core
+
+import (
+	"git.akyoto.dev/cli/q/src/errors"
+	"git.akyoto.dev/cli/q/src/expression"
+	"git.akyoto.dev/cli/q/src/scope"
+	"git.akyoto.dev/cli/q/src/token"
+)
+
+// Define defines a new variable.
+func (f *Function) Define(leaf *expression.Expression) (*scope.Variable, error) {
+	name := leaf.Token.Text(f.File.Bytes)
+
+	if f.IdentifierExists(name) {
+		return nil, errors.New(&errors.VariableAlreadyExists{Name: name}, f.File, leaf.Token.Position)
+	}
+
+	uses := token.Count(f.Body, f.File.Bytes, token.Identifier, name) - 1
+
+	if uses == 0 {
+		return nil, errors.New(&errors.UnusedVariable{Name: name}, f.File, leaf.Token.Position)
+	}
+
+	variable := &scope.Variable{
+		Name:     name,
+		Register: f.NewRegister(),
+		Alive:    uses,
+	}
+
+	return variable, nil
+}