Panic: `Recursion limit reached in occurs`

[sullyj3]

Code two_sum.an

import Vec Vec
import HashMap HashMap

two_sum (nums: Vec I32) (target: I32): Maybe (Usz, Usz) =
  complements: Ref (HashMap I32 I32) = mut HashMap.empty ()
  loop (i=0) ->
    a = nums#i
    b = target - a
    match HashMap.get_entry complements b
    | Some j -> Some (j, i)
    | None -> 
      HashMap.insert complements a i
      if i + 1 < Vec.len nums then
        recur (i + 1)
      else
        None

Causes a panic:

⮞ env RUST_BACKTRACE=1 ante two_sum.an
thread 'main' panicked at src/types/typechecker.rs:543:9:
Recursion limit reached in occurs
stack backtrace:
   0: std::panicking::begin_panic
   1: ante::types::typechecker::occurs
   2: ante::types::typechecker::typevars_match
   3: ante::types::typechecker::occurs
   4: ante::types::typechecker::typevars_match
   5: ante::types::typechecker::occurs
   6: ante::types::typechecker::typevars_match
   7: ante::types::typechecker::occurs
   8: ante::types::typechecker::typevars_match
   9: ante::types::typechecker::occurs
  10: ante::types::typechecker::typevars_match
  11: ante::types::typechecker::occurs
  12: ante::types::typechecker::typevars_match
  13: ante::types::typechecker::occurs
  14: ante::types::typechecker::typevars_match
  15: ante::types::typechecker::occurs
  16: ante::types::typechecker::typevars_match
  17: ante::types::typechecker::occurs
  18: ante::types::typechecker::typevars_match
  19: ante::types::typechecker::occurs
  20: ante::types::typechecker::typevars_match
  21: ante::types::typechecker::occurs
  22: ante::types::typechecker::typevars_match
  23: ante::types::typechecker::occurs
  24: ante::types::typechecker::typevars_match
  25: ante::types::typechecker::occurs
  26: ante::types::typechecker::occurs
  27: ante::types::typechecker::typevars_match
  28: ante::types::typechecker::occurs
  29: ante::types::typechecker::occurs
  30: ante::types::typechecker::try_unify_type_variable_with_bindings
  31: ante::types::typechecker::try_unify_with_bindings
  32: ante::types::typechecker::try_unify
  33: ante::types::typechecker::bind_irrefutable_pattern
  34: <ante::parser::ast::Definition as ante::types::typechecker::Inferable>::infer_impl
  35: ante::types::typechecker::infer_nested_definition
  36: <ante::parser::ast::Ast as ante::types::typechecker::Inferable>::infer_impl
  37: <ante::parser::ast::FunctionCall as ante::types::typechecker::Inferable>::infer_impl
  38: <ante::parser::ast::Match as ante::types::typechecker::Inferable>::infer_impl
  39: <ante::parser::ast::Ast as ante::types::typechecker::Inferable>::infer_impl
  40: ante::types::typechecker::infer
  41: <ante::parser::ast::Ast as ante::types::typechecker::Inferable>::infer_impl
  42: <ante::parser::ast::Definition as ante::types::typechecker::Inferable>::infer_impl
  43: <ante::parser::ast::Ast as ante::types::typechecker::Inferable>::infer_impl
  44: <ante::parser::ast::Match as ante::types::typechecker::Inferable>::infer_impl
  45: <ante::parser::ast::Ast as ante::types::typechecker::Inferable>::infer_impl
  46: <ante::parser::ast::Ast as ante::types::typechecker::Inferable>::infer_impl
  47: <ante::parser::ast::Definition as ante::types::typechecker::Inferable>::infer_impl
  48: <ante::parser::ast::Ast as ante::types::typechecker::Inferable>::infer_impl
  49: ante::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
fish: Job 1, 'env RUST_BACKTRACE=1 ante two_s…' terminated by signal SIGABRT (Abort)