Yeah, that's definitely a confusing part of GHCi. If you see an error message like the one in the post Prelude> 1+[2,3] <interactive>:1:1: error:

Yeah, that's definitely a confusing part of GHCi. If you see an error message like the one in the post Prelude> 1+[2,3] <interactive>:1:1: error: • Non type-variable argument in the constraint: Num [a] (Use FlexibleContexts to permit this) • When checking the inferred type it :: forall a. (Num a, Num [a]) => [a] The "line-number" is found on this line <interactive>:1:1: error: Since it's in a REPL, it is referring to the first line you entered. The more confusing part is that the important error is found here • When checking the inferred type it :: forall a. (Num a, Num [a]) => [a] where it is assumed that you know all REPL statements that don't bind to a variable are bound to a variable named "it". So the error is really saying that the whole expression 1+[2,3] has that inferred type, and that type is bad. If you load your example into a file and run GHC on it, it will produce a still confusing error message, but it will at least show you where the problems are error-message.hs:3:11: error: • No instance for (Num [a0]) arising from a use of ‘+’ • In the expression: 1 + [1, 2] In an equation for ‘badType’: badType = 1 + [1, 2] | 3 | badType = 1 + [1,2] | ^^^^^^^^^ (I've omitted another, much longer error message it spewed out which is similarly confusing)