I just noticed this and I want to make sure it's me and not a a bug.

fansh> y := Map([Int:Float]:Str#)
[:]
fansh> y.typeof
[[sys::Int:sys::Float]:sys::Str]
fansh> y[3]
null
fansh>

We create a variable y. The value of y is typed as [Int:Float]:Str. However, I try to index y at 3. This should be an error, because the key type is Int:Float, not Int. But instead of an error, I get null.

If I use the more usual syntax, I get the expected error.

fansh> z := [Int:Float]:Str[:]
[:]
fansh> z.typeof
[[sys::Int:sys::Float]:sys::Str]
fansh> z[3]
ERROR(2): Invalid args get([sys::Int:sys::Float], sys::Str?), not (sys::Int)
ERROR(2): Not a statement
fansh>

It seems as if Map.make doesn't properly initialize the object's type.

That sounds like something that's come up before, but I can't find it. I think you're right, that's a bug; as I remember it, there was a ticket some time back about make for List and Map failing to note the type info. But searching, I got sidetracked into #7. :-)

#633 is semi-related...

Actually that is the expected behavior because calling Map constructor directly is typing y as Obj:Obj? thus no compiler type checking happens when you do y[3].

Ah, so the variable is typed as Obj:Obj? but the value stored there is [[sys::Int:sys::Float]:sys::Str]. Gotcha.