# Operands

Instructions in Val IR may accept operands embodying values to be operated upon. There exists 5 types of operands:

* **Type references**: A type reference denotes a lowered type definition.
* **Basic block references**: A basic block reference denotes a basic block.
* **Constants**: A constant is a value that is computed at compile time and immutable at runtime.
* **Basic block arguments**: A basic block argument denotes the value passed to a basic block when control flow entered to its entry point.
* **Instruction results**: An instruction result denotes the one of the values produced by the evaluation of an instruction.

{% hint style="info" %}
A thin function reference is a constant because it is immutable. Similarly, the memory location of a global binding's storage is a constant.
{% endhint %}

Each basic block argument and instruction result is assigned to a unique local register in the function. The value of a register 

## Uses

An instruction `i` is said to be a *user* of an operand `o` if `o` is argument of `i`. Each occurence of an operand in one of its users is called a *use*.

Given two uses `u1` and `u2`, `u2` is sequenced after `u1` (or, equivalently, u1 is sequenced before u2) if and only if:

* the user of `u2` is sequenced after the user of `u1`, or
* `u1` and `u2` have the same user and `u1` appears before `u2`.