Running the PACK operation on a tuple (represented as a pair in Michelson, I get
$ ligo interpret -s pascaligo 'Bytes.pack((1, 2))'
0x05070700010002
The numbers 1 and 2 are serialized as 0001 and 0002, respectively.
The tuple (1,2) is represented as PAIR 1 2 in Michelson and PAIR serializes to 0x07. So why are there two 0x07 values, and not just one?
Here is a break down:
0x05 (ref).Pair 1 2 is a primitive application with 2 arguments and no annotation. The corresponding tag is 0x07.12Let's try another example. What is the encoding of the value Left 1 of type or nat bool? Per tezos-client hash data 'Left 1' of type 'or nat bool', it will be 0x05 05 05 0001, where:
05: the fixed prefix denotes a michelson data value, as above.05: the expression Left 1 is a primitive application with one argument and no annotations. The corresponding tag is also 0x05.05: the michelson primitive is Left, for which the corresponding tag is also 05.0001: encoding of the integer 1.
07 means both the Pair type constructor, and primitive. Got it. I would have though the first 07 was the primitive value and only the 2nd was the Pair type constructor, though.
Commented
Oct 5, 2020 at 11:10
Pair is not a type constructor but a data constructor. However, pair is a type constructor (admittedly, it is confusing). Lowercase keywords are types, and capitalized keywords are data constructors. Example: Pair is a constructor that constructs values of type pair x y. pair is a type constructor with two arguments.