diff --git a/example/main.zig b/example/main.zig
index 169a6cc..7f778e5 100644
--- a/example/main.zig
+++ b/example/main.zig
@@ -17,8 +17,8 @@ pub fn main() !void {
         defer rt.deinit(allocator);
 
         try rt.callEntryPoint(allocator, try rt.getEntryPointByName("main"));
-        var output: [4]f32 = undefined;
-        try rt.readOutput(f32, output[0..output.len], try rt.getResultByName("color"));
+        var output: [4]i32 = undefined;
+        try rt.readOutput(i32, output[0..output.len], try rt.getResultByName("color"));
         std.log.info("Output: Vec4{any}", .{output});
     }
     std.log.info("Successfully executed", .{});
diff --git a/example/shader.nzsl b/example/shader.nzsl
index ec65fc3..0058b30 100644
--- a/example/shader.nzsl
+++ b/example/shader.nzsl
@@ -4,18 +4,19 @@ module;
 
 struct FragOut
 {
-    [location(0)] color: vec4[f32]
+    [location(0)] color: vec4[i32]
 }
 
-fn computeColor(val: f32) -> f32
+fn fibonacci(n: i32) -> i32
 {
-	return 2.0 * val;
+    if (n <= i32(1)) return n;
+    return fibonacci(n - i32(1)) + fibonacci(n - i32(2));
 }
 
 [entry(frag)]
 fn main() -> FragOut
 {
     let output: FragOut;
-    output.color = vec4[f32](computeColor(1.0), computeColor(2.0), computeColor(3.0), computeColor(4.0));
+    output.color = vec4[i32](fibonacci(2), fibonacci(2), fibonacci(2), fibonacci(2));
     return output;
 }
diff --git a/example/shader.spv b/example/shader.spv
index afda241..bc61751 100644
Binary files a/example/shader.spv and b/example/shader.spv differ
diff --git a/example/shader.spv.txt b/example/shader.spv.txt
index 59c5a0e..1a1ffb5 100644
--- a/example/shader.spv.txt
+++ b/example/shader.spv.txt
@@ -1,65 +1,82 @@
 Version 1.0
 Generator: 2560130
-Bound: 38
+Bound: 49
 Schema: 0
       OpCapability Capability(Shader)
       OpCapability Capability(Float64)
       OpMemoryModel AddressingModel(Logical) MemoryModel(GLSL450)
-      OpEntryPoint ExecutionModel(Fragment) %18 "main" %9
-      OpExecutionMode %18 ExecutionMode(OriginUpperLeft)
+      OpEntryPoint ExecutionModel(Fragment) %16 "main" %11
+      OpExecutionMode %16 ExecutionMode(OriginUpperLeft)
       OpSource SourceLanguage(NZSL) 4198400
       OpSourceExtension "Version: 1.1"
-      OpName %10 "FragOut"
-      OpMemberName %10 0 "color"
-      OpName %9 "color"
-      OpName %17 "computeColor"
-      OpName %18 "main"
-      OpDecorate %9 Decoration(Location) 0
-      OpMemberDecorate %10 0 Decoration(Offset) 0
- %1 = OpTypeFloat 32
+      OpName %12 "FragOut"
+      OpMemberName %12 0 "color"
+      OpName %11 "color"
+      OpName %15 "fibonacci"
+      OpName %16 "main"
+      OpDecorate %11 Decoration(Location) 0
+      OpMemberDecorate %12 0 Decoration(Offset) 0
+ %1 = OpTypeInt 32 1
  %2 = OpTypePointer StorageClass(Function) %1
  %3 = OpTypeFunction %1 %2
- %4 = OpConstant %1 f32(2)
- %5 = OpTypeVoid
- %6 = OpTypeFunction %5
- %7 = OpTypeVector %1 4
- %8 = OpTypePointer StorageClass(Output) %7
-%10 = OpTypeStruct %7
-%11 = OpTypePointer StorageClass(Function) %10
-%12 = OpTypeInt 32 1
-%13 = OpConstant %12 i32(0)
-%14 = OpConstant %1 f32(1)
-%15 = OpConstant %1 f32(3)
-%16 = OpConstant %1 f32(4)
-%35 = OpTypePointer StorageClass(Function) %7
- %9 = OpVariable %8 StorageClass(Output)
-%17 = OpFunction %1 FunctionControl(0) %3
-%19 = OpFunctionParameter %2
-%20 = OpLabel
-%21 = OpLoad %1 %19
-%22 = OpFMul %1 %4 %21
-      OpReturnValue %22
-      OpFunctionEnd
-%18 = OpFunction %5 FunctionControl(0) %6
+ %4 = OpConstant %1 i32(1)
+ %5 = OpTypeBool
+ %6 = OpConstant %1 i32(2)
+ %7 = OpTypeVoid
+ %8 = OpTypeFunction %7
+ %9 = OpTypeVector %1 4
+%10 = OpTypePointer StorageClass(Output) %9
+%12 = OpTypeStruct %9
+%13 = OpTypePointer StorageClass(Function) %12
+%14 = OpConstant %1 i32(0)
+%46 = OpTypePointer StorageClass(Function) %9
+%11 = OpVariable %10 StorageClass(Output)
+%15 = OpFunction %1 FunctionControl(0) %3
+%17 = OpFunctionParameter %2
+%18 = OpLabel
+%19 = OpVariable %2 StorageClass(Function)
+%20 = OpVariable %2 StorageClass(Function)
+%24 = OpLoad %1 %17
+%25 = OpSLessThanEqual %5 %24 %4
+      OpSelectionMerge %21 SelectionControl(0)
+      OpBranchConditional %25 %22 %23
+%22 = OpLabel
+%26 = OpLoad %1 %17
+      OpReturnValue %26
 %23 = OpLabel
-%24 = OpVariable %11 StorageClass(Function)
-%25 = OpVariable %2 StorageClass(Function)
-%26 = OpVariable %2 StorageClass(Function)
-%27 = OpVariable %2 StorageClass(Function)
-%28 = OpVariable %2 StorageClass(Function)
-      OpStore %25 %14
-%29 = OpFunctionCall %1 %17 %25
-      OpStore %26 %4
-%30 = OpFunctionCall %1 %17 %26
-      OpStore %27 %15
-%31 = OpFunctionCall %1 %17 %27
-      OpStore %28 %16
-%32 = OpFunctionCall %1 %17 %28
-%33 = OpCompositeConstruct %7 %29 %30 %31 %32
-%34 = OpAccessChain %35 %24 %13
-      OpStore %34 %33
-%36 = OpLoad %10 %24
-%37 = OpCompositeExtract %7 %36 0
-      OpStore %9 %37
+      OpBranch %21
+%21 = OpLabel
+%27 = OpLoad %1 %17
+%28 = OpISub %1 %27 %4
+      OpStore %19 %28
+%29 = OpFunctionCall %1 %15 %19
+%30 = OpLoad %1 %17
+%31 = OpISub %1 %30 %6
+      OpStore %20 %31
+%32 = OpFunctionCall %1 %15 %20
+%33 = OpIAdd %1 %29 %32
+      OpReturnValue %33
+      OpFunctionEnd
+%16 = OpFunction %7 FunctionControl(0) %8
+%34 = OpLabel
+%35 = OpVariable %13 StorageClass(Function)
+%36 = OpVariable %2 StorageClass(Function)
+%37 = OpVariable %2 StorageClass(Function)
+%38 = OpVariable %2 StorageClass(Function)
+%39 = OpVariable %2 StorageClass(Function)
+      OpStore %36 %6
+%40 = OpFunctionCall %1 %15 %36
+      OpStore %37 %6
+%41 = OpFunctionCall %1 %15 %37
+      OpStore %38 %6
+%42 = OpFunctionCall %1 %15 %38
+      OpStore %39 %6
+%43 = OpFunctionCall %1 %15 %39
+%44 = OpCompositeConstruct %9 %40 %41 %42 %43
+%45 = OpAccessChain %46 %35 %14
+      OpStore %45 %44
+%47 = OpLoad %12 %35
+%48 = OpCompositeExtract %9 %47 0
+      OpStore %11 %48
       OpReturn
       OpFunctionEnd
diff --git a/test/functions.zig b/test/functions.zig
new file mode 100644
index 0000000..967d2c4
--- /dev/null
+++ b/test/functions.zig
@@ -0,0 +1,162 @@
+const std = @import("std");
+const root = @import("root.zig");
+const compileNzsl = root.compileNzsl;
+const case = root.case;
+
+test "Simple function calls" {
+    const allocator = std.testing.allocator;
+    const types = [_]type{ i32, u32, f32, f64 };
+
+    inline for (types) |T| {
+        const n = case.random(T);
+
+        const shader = try std.fmt.allocPrint(
+            allocator,
+            \\ [nzsl_version("1.1")]
+            \\ [feature(float64)]
+            \\ module;
+            \\ 
+            \\ struct FragOut
+            \\ {{
+            \\     [location(0)] color: vec4[{s}]
+            \\ }}
+            \\
+            \\ fn value() -> {s}
+            \\ {{
+            \\     return {d};
+            \\ }}
+            \\
+            \\ [entry(frag)]
+            \\ fn main() -> FragOut
+            \\ {{
+            \\     let output: FragOut;
+            \\     output.color = vec4[{s}](value(), value(), value(), value());
+            \\     return output;
+            \\ }}
+        ,
+            .{
+                @typeName(T),
+                @typeName(T),
+                n,
+                @typeName(T),
+            },
+        );
+        defer allocator.free(shader);
+        const code = try compileNzsl(allocator, shader);
+        defer allocator.free(code);
+        try case.expectOutput(T, 4, code, "color", &.{ n, n, n, n });
+    }
+}
+
+test "Nested function calls" {
+    const allocator = std.testing.allocator;
+    const types = [_]type{ i32, u32, f32, f64 };
+
+    inline for (types) |T| {
+        const n = case.random(T);
+
+        const shader = try std.fmt.allocPrint(
+            allocator,
+            \\ [nzsl_version("1.1")]
+            \\ [feature(float64)]
+            \\ module;
+            \\ 
+            \\ struct FragOut
+            \\ {{
+            \\     [location(0)] color: vec4[{s}]
+            \\ }}
+            \\
+            \\ fn deepValue() -> {s}
+            \\ {{
+            \\     return {d};
+            \\ }}
+            \\
+            \\ fn value() -> {s}
+            \\ {{
+            \\     return deepValue();
+            \\ }}
+            \\
+            \\ [entry(frag)]
+            \\ fn main() -> FragOut
+            \\ {{
+            \\     let output: FragOut;
+            \\     output.color = vec4[{s}](value(), value(), value(), value());
+            \\     return output;
+            \\ }}
+        ,
+            .{
+                @typeName(T),
+                @typeName(T),
+                n,
+                @typeName(T),
+                @typeName(T),
+            },
+        );
+        defer allocator.free(shader);
+        const code = try compileNzsl(allocator, shader);
+        defer allocator.free(code);
+        try case.expectOutput(T, 4, code, "color", &.{ n, n, n, n });
+    }
+}
+
+test "Recursive function calls" {
+    const allocator = std.testing.allocator;
+    const types = [_]type{ i32, u32, f32, f64 };
+
+    inline for (types) |T| {
+        const iterations = 10;
+
+        const fib = struct {
+            fn onacci(n: T) T {
+                if (n <= 0) return n;
+                return onacci(n - 1) + onacci(n - 2);
+            }
+        };
+        const expected = fib.onacci(iterations);
+
+        const shader = try std.fmt.allocPrint(
+            allocator,
+            \\ [nzsl_version("1.1")]
+            \\ [feature(float64)]
+            \\ module;
+            \\ 
+            \\ struct FragOut
+            \\ {{
+            \\     [location(0)] color: vec4[{s}]
+            \\ }}
+            \\
+            \\ fn fibonacci(n: {s}) -> {s}
+            \\ {{
+            \\     if (n <= {s}(1)) return n;
+            \\     return fibonacci(n - {s}(1)) + fibonacci(n - {s}(2));
+            \\ }}
+            \\
+            \\ [entry(frag)]
+            \\ fn main() -> FragOut
+            \\ {{
+            \\     let output: FragOut;
+            \\     output.color = vec4[{s}](fibonacci({d}), fibonacci({d}), fibonacci({d}), fibonacci({d}));
+            \\     return output;
+            \\ }}
+        ,
+            .{
+                @typeName(T),
+                @typeName(T),
+                @typeName(T),
+                @typeName(T),
+                @typeName(T),
+                @typeName(T),
+                @typeName(T),
+                iterations,
+                iterations,
+                iterations,
+                iterations,
+            },
+        );
+        defer allocator.free(shader);
+        std.debug.print("{s}\n\n", .{shader});
+        const code = try compileNzsl(allocator, shader);
+        defer allocator.free(code);
+        try case.expectOutput(T, 4, code, "color", &.{ expected, expected, expected, expected });
+    }
+}
diff --git a/test/root.zig b/test/root.zig
index 6c7ec9c..becad8d 100644
--- a/test/root.zig
+++ b/test/root.zig
@@ -59,5 +59,6 @@ test {
     std.testing.refAllDecls(@import("basics.zig"));
     std.testing.refAllDecls(@import("branching.zig"));
     std.testing.refAllDecls(@import("casts.zig"));
+    std.testing.refAllDecls(@import("functions.zig"));
     std.testing.refAllDecls(@import("maths.zig"));
 }