How to convert bool/str/float to float?

[Moonbase59]

Asked a few people, read many pages in The Book, but don’t get it: I need to be backwards compatible with a metadata variable that used to be boolean or boolean in a string, and is now a float value.

In Python, that was easy, but how to do in Liquidsoap? I didn’t even find something like type or typeof so I could ask LS for the variable type and then use an appropriate function.

Python code:

# Need to handle pre-version 3.0.0 `liq_blankskip`: was bool, is now float`
def float_blankskip(v):
    if isinstance(v, bool):
        return float(v) * args.blankskip  # True=1, False=0
    elif isinstance(v, str):
        try:
            return float(v)
        except ValueError:
            if v.lower() == 'true':
                return args.blankskip
            else:
                return 0.0
    else:
        return v

args.blankskip is a float # seconds here.

Any guru there who can help me with this?

[vitoyucepi]

If I were you, then I would convert everything to string, because every other type has a convenient to string conversion and then parse the string.

def something_to_float(value)
  value_string = string.case(string(value))
  possible_float =
    try
      float_of_string(value_string)
    catch _ do
      null()
    end
  possible_bool =
    try
      bool_of_string(value_string) ? 1. : 0.
    catch _ do
      null()
    end
  possible_float ?? possible_bool ?? 0.
end

Tests

a = true
b = false
c = "true"
d = "false"
e = "True"
f = "False"
g = "TRUE"
h = "FALSE"
i = 1.
j = -1.
k = "1."
l = "-1."
m = 1
n = -1
o = "1"
p = "-1"

def test(a)
  print(a)
  b = string.case(string(a))
  print(b)
  c =
    try
      float_of_string(b)
    catch _ do
      null()
    end
  d =
    try
      bool_of_string(b) ? 1. : 0.
    catch _ do
      null()
    end
  e = c ?? d
  print(e)
  print("")
end

test(a)
test(b)
test(c)
test(d)
test(e)
test(f)
test(g)
test(h)
test(i)
test(j)
test(k)
test(l)
test(m)
test(n)
test(o)
test(p)

[Moonbase59]

Fantastic. Thanks for all the help! There’s much to learn… ;-)

[toots]

This looks great @vitoyucepi. Python, ruby and JS typically have dynamic type conversion which makes these kind of operations really straight forward. However, they also come with some issues, typically having stuff converted to NaN without knowing because some of the input data is not what you expect it to be.

Static typing, which is OCaml, liquidsoap but also C and C++, typically require a little more care to handle errors and exceptions explicitly.

[Moonbase59]

@vitoyucepi Trying this out, I get:

At autocue.cue_file.liq, line 219, char 34-36:
  possible_float ?? possible_bool ?? 0.

Error 2: Parse error

Is it possible we can’t use ?? twice in a row?

[Moonbase59]

Put parentheses around, and it worked ;-)

  (possible_float ?? possible_bool) ?? 0.