diff --git a/src/ssa/Block.go b/src/ssa/Block.go
index 30d854b..32ac6dd 100644
--- a/src/ssa/Block.go
+++ b/src/ssa/Block.go
@@ -1,11 +1,12 @@
 package ssa
 
+// Block is a list of instructions that can be targeted in branches.
 type Block struct {
-	Entry        []*Block
 	Instructions []Instruction
-	Exit         []*Block
 }
 
-func (b *Block) Append(instr Instruction) {
+// Append adds a new instruction to the block.
+func (b *Block) Append(instr Instruction) *Instruction {
 	b.Instructions = append(b.Instructions, instr)
+	return &b.Instructions[len(b.Instructions)-1]
 }
\ No newline at end of file
diff --git a/src/ssa/Function.go b/src/ssa/Function.go
index 1831743..d5df02a 100644
--- a/src/ssa/Function.go
+++ b/src/ssa/Function.go
@@ -1,5 +1,13 @@
 package ssa
 
+// Function is a list of basic blocks.
 type Function struct {
 	Blocks []*Block
+}
+
+// AddBlock adds a new block to the function.
+func (f *Function) AddBlock() *Block {
+	block := &Block{}
+	f.Blocks = append(f.Blocks, block)
+	return block
 }
\ No newline at end of file
diff --git a/src/ssa/Index.go b/src/ssa/Index.go
deleted file mode 100644
index 9f27529..0000000
--- a/src/ssa/Index.go
+++ /dev/null
@@ -1,3 +0,0 @@
-package ssa
-
-type Index = uint16
\ No newline at end of file
diff --git a/src/ssa/Instruction.go b/src/ssa/Instruction.go
index dcccd4a..76e8e38 100644
--- a/src/ssa/Instruction.go
+++ b/src/ssa/Instruction.go
@@ -1,11 +1,28 @@
 package ssa
 
-// Instruction is a "fat struct" for performance reasons.
+import (
+	"fmt"
+)
+
+// Instruction is a single instruction in a basic block.
+// It is implemented as a "fat struct" for performance reasons.
 // It contains all the fields necessary to represent all instruction types.
 type Instruction struct {
-	Type       Type
-	Parameters []Index
-	Int        int64
-	Float      float64
-	String     string
+	Type  Type
+	Args  []*Instruction
+	Int   int64
+	Float float64
+	Text  string
+}
+
+// String returns a human-readable representation of the instruction.
+func (i *Instruction) String() string {
+	switch i.Type {
+	case Int:
+		return fmt.Sprintf("%d", i.Int)
+	case Add:
+		return fmt.Sprintf("%s + %s", i.Args[0], i.Args[1])
+	default:
+		return ""
+	}
 }
\ No newline at end of file
diff --git a/src/ssa/Type.go b/src/ssa/Type.go
index c1aba45..1ea82b1 100644
--- a/src/ssa/Type.go
+++ b/src/ssa/Type.go
@@ -1,5 +1,6 @@
 package ssa
 
+// Type represents the instruction type.
 type Type byte
 
 const (
@@ -24,6 +25,10 @@ const (
 	Shl
 	Shr
 
+	// Branch
+	If
+	Jump
+
 	// Special
 	Call
 	Phi
diff --git a/src/ssa/bench_test.go b/src/ssa/bench_test.go
index 03799f3..d959299 100644
--- a/src/ssa/bench_test.go
+++ b/src/ssa/bench_test.go
@@ -8,6 +8,8 @@ import (
 	"git.urbach.dev/go/assert"
 )
 
+// This benchmark compares the performance of fat structs and interfaces.
+// It allocates `n` objects where `n` must be divisible by 2.
 const n = 100
 
 type FatStruct struct {
diff --git a/src/ssa/ssa_test.go b/src/ssa/ssa_test.go
index 8b74df0..7455424 100644
--- a/src/ssa/ssa_test.go
+++ b/src/ssa/ssa_test.go
@@ -4,11 +4,19 @@ import (
 	"testing"
 
 	"git.urbach.dev/cli/q/src/ssa"
+	"git.urbach.dev/go/assert"
 )
 
 func TestBlock(t *testing.T) {
-	block := &ssa.Block{}
-	block.Append(ssa.Instruction{Type: ssa.Int, Int: 1})
-	block.Append(ssa.Instruction{Type: ssa.Int, Int: 2})
-	block.Append(ssa.Instruction{Type: ssa.Add, Parameters: []ssa.Index{0, 1}})
+	f := ssa.Function{}
+	block := f.AddBlock()
+	a := block.Append(ssa.Instruction{Type: ssa.Int, Int: 1})
+	b := block.Append(ssa.Instruction{Type: ssa.Int, Int: 2})
+	c := block.Append(ssa.Instruction{Type: ssa.Add, Args: []*ssa.Instruction{a, b}})
+	assert.Equal(t, c.String(), "1 + 2")
+}
+
+func TestInvalidInstruction(t *testing.T) {
+	instr := ssa.Instruction{}
+	assert.Equal(t, instr.String(), "")
 }
\ No newline at end of file