I’m hoping smarter eyes than mine can help me resolve this issue. I am attempting to convert a decimal to an integer. The Decimal implementation uses guard clauses to decide if such as conversion is possible (good!). But for some reason I’m seeing guard clauses fail even when the data looks like it should pass. Here’s the example:

# A decimal. Shouldn't be able to be converted to an integer
# but it looks like the guards for the third clause should match and I
# don't know why they aren't!
iex> d = Decimal.new("1234.50")
#Decimal<1234.50>

# Here's what the struct underneath looks like:
iex> inspect d, structs: false
"%{__struct__: Decimal, coef: 123450, exp: -2, sign: 1}"

# Lets check the remainder of the coef
iex> Kernel.rem(d.coef,10)
0

# Error raises on conversion suggesting no guards match but
# I think the third clause should match?
iex> Decimal.to_integer d                     
** (FunctionClauseError) no function clause matching in Decimal.to_integer/1    
    
    The following arguments were given to Decimal.to_integer/1:
    
        # 1
        #Decimal<1234.5>
    
    Attempted function clauses (showing 3 out of 3):
    
        def to_integer(%Decimal{sign: sign, coef: coef, exp: 0}) when is_integer(coef)
        def to_integer(%Decimal{sign: sign, coef: coef, exp: exp}) when is_integer(coef) and exp > 0
        def to_integer(%Decimal{sign: sign, coef: coef, exp: exp}) when is_integer(coef) and exp < 0 and rem(coef, 10) == 0
    
    (decimal 2.0.0) lib/decimal.ex:1322: Decimal.to_integer/1

But in my example is_integer(coef) == true and exp < 0 == true and rem(coef, 10) == 0 so why isn’t this clause being executed?

Probably an issue with me staring at a screen for too long so any guidance appreciated.