elixir-guards.md

The Erlang VM only allows a limited set of expressions as guards:

• comparison operators (==, !=, ===, !==, >, <, <=, >=);

• boolean operators (and, or) and negation operators (not, !);

• arithmetic operators (+, -, *, /);

• <> and ++ as long as the left side is a literal;

• the in operator;

• all the following type check functions:

  • is_atom/1
  • is_binary/1
  • is_bitstring/1
  • is_boolean/1
  • is_float/1
  • is_function/1
  • is_function/2
  • is_integer/1
  • is_list/1
  • is_number/1
  • is_pid/1
  • is_port/1
  • is_record/2
  • is_record/3
  • is_reference/1
  • is_tuple/1
  • is_exception/1

• plus these functions:

  • abs(Number)
  • bit_size(Bitstring)
  • byte_size(Bitstring)
  • div(Number, Number)
  • elem(Tuple, n)
  • float(Term)
  • hd(List)
  • length(List)
  • node()
  • node(Pid|Ref|Port)
  • rem(Number, Number)
  • round(Number)
  • self()
  • size(Tuple|Bitstring)
  • tl(List)
  • trunc(Number)
  • tuple_size(Tuple)