layout_vars.nim: type mismatch
I am struggling to compile the basic examples in the test folder. I get the following:
```
$ nim c --threads:on sample01_welcome.nim
....
/home/jose/.nimble/pkgs/nimx-#head/nimx/layout_vars.nim(19, 32) Error: type mismatch: got <Variable>
but expected one of: 
proc newExpression(constant: float = 0): Expression
  first type mismatch at position: 1
  required type for constant: float
  but expression 'left(phs)' is of type: Variable
proc newExpression(term: Term; constant: float = 0): Expression
  first type mismatch at position: 1
  required type for term: Term
  but expression 'left(phs)' is of type: Variable
proc newExpression(terms: seq[Term]; constant: float = 0): Expression
  first type mismatch at position: 1
  required type for terms: seq[Term]
  but expression 'left(phs)' is of type: Variable
```

I am using: nim 1.2.0. And I am using a mix of versions: I install ttf from github because I was having a similar problem. I installed nimx with `nimble install nimx@#head` and later from github.