ailang-debug

name	AILANG Debug
description	Debug AILANG code errors. Use when you encounter type errors, parse errors, or runtime failures in AILANG programs.

AILANG Debug

Fix common AILANG errors quickly.

Quick Reference

Error	Cause	Fix
undefined variable: print	Not in entry module	Use entry module or import std/io (print)
undefined variable: println	Wrong function name	Use print not println
undefined variable: map	Not imported	import std/list (map) or write recursive
No instance for Num[string]	print(42)	Use print(show(42))
expected }, got let	Missing semicolon	Add ; between statements
unexpected token: for	No loops in AILANG	Use recursion instead
unexpected token: in	No for x in xs	Use match xs { ... }

Decision Tree

Error message?
│
├─ "undefined variable: X"
│   └─ Is X a builtin?
│       ├─ Yes → Import it: ailang builtins list | grep X
│       └─ No → Check spelling, define it
│
├─ "expected }, got ..."
│   └─ Missing semicolon between statements
│       Fix: let x = 1; let y = 2; x + y
│
├─ "No instance for Num[string]"
│   └─ Passing number to string function
│       Fix: print(show(42)) not print(42)
│
├─ "unexpected token: for/while/in"
│   └─ AILANG has no loops!
│       Fix: Use recursion with match
│
└─ Parse error with braces
    └─ Unmatched { } or missing expression
        Fix: Check all blocks are closed

Common Fixes

1. Missing Semicolons

-- WRONG
export func main() -> () ! {IO} {
  let x = 10
  let y = 20
  print(show(x + y))
}

-- CORRECT (semicolons between statements)
export func main() -> () ! {IO} {
  let x = 10;
  let y = 20;
  print(show(x + y))
}

2. Print Needs String

-- WRONG: print expects string
print(42)

-- CORRECT: convert with show()
print(show(42))

3. No Loops - Use Recursion

-- WRONG: no for loops
for i in range(5) { print(show(i)) }

-- CORRECT: recursive function
export func printRange(n: int) -> () ! {IO} {
  if n <= 0 then () else {
    print(show(n));
    printRange(n - 1)
  }
}

4. Import Standard Library

-- WRONG: map not in scope
let doubled = map(\x. x * 2, nums)

-- CORRECT: import from std/list
import std/list (map)
let doubled = map(\x. x * 2, nums)

-- OR: write it yourself (recursion)
export func myMap[a,b](f: func(a) -> b, xs: [a]) -> [b] {
  match xs {
    [] => [],
    hd :: tl => f(hd) :: myMap(f, tl)
  }
}

Debugging Workflow

1. Type-check first (faster feedback):

   ailang check file.ail
   

2. Read error location - line:column tells you where

3. Check the pattern above for your error type

4. Use REPL for quick tests:

   ailang repl
   > show(42)
   > 1 + 2
   > :type \x. x * 2
   

5. List builtins to find imports (CLI is source of truth):

   # SOURCE OF TRUTH: Full documentation with examples
   ailang builtins list --verbose --by-module
   
   # Search for specific function with full docs
   ailang builtins list --verbose | grep -A 10 "map"
   
   # See a specific module's functions
   ailang builtins list --verbose --by-module | grep -A 30 "std/list"
   

Resources

Always prefer CLI commands (ailang prompt, ailang builtins list --verbose) over static docs - they're always up-to-date.

See resources/error_catalog.md for additional error patterns.