Type deduction causes formula CT error

[Vindaar]

Reported by KosKosynsky on the #science channel (added steps for a minimal repro):

import datamancer, strutils

var flota = toDf({"x" : @["a", "b"], "y" : @["1", "2"], "z" : @[1, 3]})
let flota_cols = flota.getKeys()
for i_col in flota_cols:
  if (flota[i_col].nativeColKind == colString):
    flota = flota.mutate(f{string -> string: i_col ~ strip(idx(i_col))})

echo flota

which fails in the determineTypeFromProc helper, which tries to look at the default arguments for type info from the latest argument to strip (we shouldn't even have to look at that, but in any case shouldn't fail!).

The issue is that we assume that the last field of a default nnkIdentDefs is a symbol, but it's not in this case. The offending node is:

IdentDefs
  Sym "leading"
  Empty
  Ident "true" 

from the params sequence:

  IdentDefs
    Sym "s"
    Sym "string"
    Empty
  IdentDefs
    Sym "leading"
    Empty
    Ident "true"
  IdentDefs
    Sym "trailing"
    Empty
    Ident "true"
  IdentDefs
    Sym "chars"
    BracketExpr
      Sym "set"
      Sym "char"
    Ident "Whitespace"

Instead of

        typ = pArg[pArg.len - 1].getType # use the default values type

we should check if the node is a type first before calling getType.

Question: what to do for idents?

Just find a way to fix it... :)

[Vindaar]

The special case for bool types has been addressed in #46, but there are probably other cases that need attention.

[Vindaar]

Note: the code snippet in the issue works nowadays. I need to check the code again to see if should in theory work in general cases now and if so close this issue.