Added eval package

src/eval/Kind.go

@@ -0,0 +1,11 @@
+package eval
+
+type Kind uint8
+
+const (
+	Invalid  Kind = iota // Invalid is an invalid value.
+	Number               // Number is an immediately encoded value stored together with the instruction.
+	Register             // Register is a CPU register.
+	Memory               // Memory is an area in the RAM.
+	Label                // Label is a reference to a name that can only be resolved once the program is fully compiled.
+)

src/eval/Value.go

@@ -0,0 +1,32 @@
+package eval
+
+import (
+	"git.urbach.dev/cli/q/src/asm"
+	"git.urbach.dev/cli/q/src/cpu"
+	"git.urbach.dev/cli/q/src/types"
+)
+
+// Value combines a register with its data type.
+type Value struct {
+	Type     types.Type
+	Label    string
+	Number   int
+	Memory   asm.Memory
+	Register cpu.Register
+	Alive    uint8
+	Kind     Kind
+}
+
+// IsAlive returns true if the Value is still alive.
+func (v *Value) IsAlive() bool {
+	return v.Alive > 0
+}
+
+// Use reduces the lifetime counter by one.
+func (v *Value) Use() {
+	if v.Alive == 0 {
+		panic("incorrect number of value use calls")
+	}
+
+	v.Alive--
+}