diff --git a/opt.wat b/opt.wat
deleted file mode 100644
index 90d212b..0000000
--- a/opt.wat
+++ /dev/null
@@ -1,25 +0,0 @@
-(module
-  (type (;0;) (func (param i32 i32 i32 i32) (result i32)))
-  (type (;1;) (func))
-  (import "wasi_snapshot_preview1" "fd_write" (func (;0;) (type 0)))
-  (func (;1;) (type 1)
-    i32.const 1028
-    i32.const 0
-    i32.store
-    i32.const 1032
-    i32.const 2
-    i32.store
-    i32.const 1
-    i32.const 1028
-    i32.const 2
-    i32.const 1024
-    call 0
-    drop
-  )
-  (table (;0;) 0 0 funcref)
-  (memory (;0;) 65536 65536)
-  (export "memory" (memory 0))
-  (export "__indirect_function_table" (table 0))
-  (export "_start" (func 1))
-  (data (;0;) (i32.const 0) "a\0a")
-)
\ No newline at end of file
diff --git a/src/ast.ts b/src/ast.ts
index 45e203d..e0933d5 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -300,6 +300,7 @@ export const BUILTINS = [
   "Bool",
   "true",
   "false",
+  "trap",
   // Intrinsics:
   "__i32_store",
   "__i64_store",
diff --git a/src/error.ts b/src/error.ts
index fce66b5..d171714 100644
--- a/src/error.ts
+++ b/src/error.ts
@@ -47,16 +47,17 @@ function renderError(input: string, e: CompilerError) {
     throw Error(`Span out of bounds: ${e.span.start}..${e.span.end}`);
   }
   const lineIdx = lineSpans.indexOf(line);
+  const lineNo = lineIdx + 1;
   console.error(`error: ${e.message}`);
 
-  console.error(`${lineIdx} | ${spanToSnippet(input, line)}`);
+  console.error(`${lineNo} | ${spanToSnippet(input, line)}`);
   const startRelLine =
     e.span.start === Number.MAX_SAFE_INTEGER ? 0 : e.span.start - line.start;
 
   const spanLength = min(e.span.end, line.end) - e.span.start;
 
   console.error(
-    `${" ".repeat(String(lineIdx).length)}   ${" ".repeat(
+    `${" ".repeat(String(lineNo).length)}   ${" ".repeat(
       startRelLine
     )}${"^".repeat(spanLength)}`
   );
diff --git a/src/index.ts b/src/index.ts
index d8541ac..045eb1f 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -9,23 +9,84 @@ import { writeModuleWatToString } from "./wasm/wat";
 import fs from "fs";
 import { exec } from "child_process";
 
-const input = `
+const INPUT = `
 function main() = (
-  prInt(0);
-  prInt(1);
-  prInt(9);
-  prInt(10);
-  prInt(100);
+  prIntln(0);
+  prIntln(1);
+  prIntln(9);
+  prIntln(2352353);
+  prIntln(100);
 );
 
-function prInt(a: Int) = (
-
+function prIntln(x: Int) = (
+  prInt(x);
+  print("\n");
 );
 
-function uwu(): (Int, Int) = (0, 0);
+function stringForDigit(x: Int): String = 
+  if x == 0 then "0"
+  else if x == 1 then "1"
+  else if x == 2 then "2"
+  else if x == 3 then "3"
+  else if x == 4 then "4"
+  else if x == 5 then "5"
+  else if x == 6 then "6"
+  else if x == 7 then "7"
+  else if x == 8 then "8"
+  else if x == 9 then "9"
+  else trap();
+
+function log10(x: Int): Int = (
+  let i = 0;
+  loop (
+    if x < 10 then break;
+    i = i + 1;
+    x = x / 10;
+  );
+  i
+);
+
+function pow(base: Int, exp: Int): Int = (
+  let acc = 1;
+  loop (
+    if exp == 0 then break;
+    acc = acc * base;
+    exp = exp - 1;
+  );
+  acc
+);
+
+function prInt(x: Int) = (
+  let mag = log10(x);
+
+  loop (
+    if mag == 0 then break;
+    let base = pow(10, mag);
+
+    let digit = x / base;
+    print(stringForDigit(digit));
+
+    x = x % base;
+    mag = mag - 1;
+  );
+
+  print(stringForDigit(x % 10));
+);
+
+function println(s: String) = (
+  print(s);
+  print("\n");
+);
 `;
 
 function main() {
+  let input: string;
+  if (process.argv.length > 2) {
+    input = fs.readFileSync(process.argv[2], { encoding: "utf-8" });
+  } else {
+    input = INPUT;
+  }
+
   withErrorHandler(input, () => {
     const start = Date.now();
 
diff --git a/src/lower.ts b/src/lower.ts
index 58f9d31..e8d1e4a 100644
--- a/src/lower.ts
+++ b/src/lower.ts
@@ -203,6 +203,7 @@ type FuncContext = {
   cx: Context;
   item: Item;
   func: FunctionDef;
+  wasmType: wasm.FuncType;
   wasm: wasm.Func;
   varLocations: VarLocation[];
   loopDepths: Map<LoopId, number>;
@@ -231,6 +232,7 @@ function lowerFunc(cx: Context, item: Item, func: FunctionDef) {
     cx,
     item,
     func,
+    wasmType,
     wasm: wasmFunc,
     varLocations: paramLocations,
     loopDepths: new Map(),
@@ -265,7 +267,7 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
       lowerExpr(fcx, instrs, expr.rhs);
       const types = wasmTypeForBody(expr.rhs.ty!);
 
-      const local = fcx.wasm.locals.length;
+      const local = fcx.wasm.locals.length + fcx.wasmType.params.length;
 
       fcx.wasm.locals.push(...types);
 
@@ -498,6 +500,10 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
 
       if (expr.lhs.value.res!.kind === "builtin") {
         switch (expr.lhs.value.res!.name) {
+          case "trap": {
+            instrs.push({ kind: "unreachable" });
+            break exprKind;
+          }
           case "__i32_load": {
             lowerExpr(fcx, instrs, expr.args[0]);
             instrs.push({ kind: "i64.load", imm: {} });
diff --git a/src/typeck.ts b/src/typeck.ts
index 0a0dcb2..cdedebc 100644
--- a/src/typeck.ts
+++ b/src/typeck.ts
@@ -61,6 +61,8 @@ function typeOfBuiltinValue(name: BuiltinName, span: Span): Ty {
       return TY_BOOL;
     case "print":
       return mkTyFn([TY_STRING], TY_UNIT);
+    case "trap":
+      return mkTyFn([], TY_NEVER);
     case "__i32_store":
       return mkTyFn([TY_I32, TY_I32], TY_UNIT);
     case "__i64_store":
diff --git a/src/wasm/wat.ts b/src/wasm/wat.ts
index e39ebc0..48dc5d6 100644
--- a/src/wasm/wat.ts
+++ b/src/wasm/wat.ts
@@ -541,11 +541,13 @@ function printImport(import_: Import, f: Formatter) {
   });
 }
 
-function printFunction(func: Func, f: Formatter) {
+function printFunction(func: Func, idx: number, f: Formatter) {
   f.sexpr(() => {
     f.keyword("func");
     printId(func._name, f);
 
+    f.word(`(;${idx};)`, chalk.gray);
+
     f.sexpr(() => {
       f.keyword("type");
       f.type(func.type);
@@ -678,9 +680,9 @@ function printModule(module: Module, f: Formatter) {
       printImport(import_, f);
     });
 
-    module.funcs.forEach((func) => {
+    module.funcs.forEach((func, i) => {
       breakIfAny();
-      printFunction(func, f);
+      printFunction(func, i + module.imports.length, f);
     });
 
     module.tables.forEach((table) => {
diff --git a/test.nil b/test.nil
new file mode 100644
index 0000000..67b19cf
--- /dev/null
+++ b/test.nil
@@ -0,0 +1,67 @@
+function main() = (
+  prIntln(0);
+  prIntln(1);
+  prIntln(9);
+  prIntln(2352353);
+  prIntln(100);
+);
+
+function prIntln(x: Int) = (
+  prInt(x);
+  print("\n");
+);
+
+function stringForDigit(x: Int): String = 
+  if x == 0 then "0"
+  else if x == 1 then "1"
+  else if x == 2 then "2"
+  else if x == 3 then "3"
+  else if x == 4 then "4"
+  else if x == 5 then "5"
+  else if x == 6 then "6"
+  else if x == 7 then "7"
+  else if x == 8 then "8"
+  else if x == 9 then "9"
+  else trap();
+
+function log10(x: Int): Int = (
+  let i = 0;
+  loop (
+    if x < 10 then break;
+    i = i + 1;
+    x = x / 10;
+  );
+  i
+);
+
+function pow(base: Int, exp: Int): Int = (
+  let acc = 1;
+  loop (
+    if exp == 0 then break;
+    acc = acc * base;
+    exp = exp - 1;
+  );
+  acc
+);
+
+function prInt(x: Int) = (
+  let mag = log10(x);
+
+  loop (
+    if mag == 0 then break;
+    let base = pow(10, mag);
+
+    let digit = x / base;
+    print(stringForDigit(digit));
+
+    x = x % base;
+    mag = mag - 1;
+  );
+
+  print(stringForDigit(x % 10));
+);
+
+function println(s: String) = (
+  print(s);
+  print("\n");
+);
\ No newline at end of file