eval_list fails on the empty list

[ChrisEPhifer]

Consider the following SAWScript (note that Bit was chosen arbitrarily; any other monomorphization will also fail):

eval_list {{ [] : [0]Bit }};

This results in an error and crash: saw: arithmetic underflow.

[brianhuffman]

The problem is in the expression traverse (scNat sc) [0 .. fromInteger n - 1] in this line of code:

saw-script/src/SAWScript/Builtins.hs

Line 1167 in 2631892

idxs <- io $ traverse (scNat sc) [0 .. fromInteger n - 1]

Function scNat takes an argument of type Natural. The expression [0 .. fromInteger n - 1] is intended to evaluate to the empty list when n = 0, but the upper bound fromInteger 0 - 1 underflows on type Natural, yielding the error.

We could fix this by replacing [0 .. fromInteger n - 1] with map fromInteger [0 .. n - 1].