Haskell synonym of Plutarch types

Several sections of the guide use the terminology “Haskell synonym”. What does it mean? It’s simply the Haskell type that is supposed to correspond to a Plutarch type. There doesn’t necessarily have to be some sort of concrete connection (though there can be, using PLift/PConstant) - it’s merely a connection you can establish mentally.

This detail does come into play in concrete use cases though. After compiling your Plutarch code to a Script, when you pass Haskell data types as arguments to the Script - they obviously need to correspond to the actual arguments of the Plutarch code. For example, if the Plutarch code is a function taking PByteString, after compilation to Script, you should pass in the Haskell data type that actually shares the same representation as PByteString - the “Haskell synonym”, so to speak. In this case, that’s ByteString*.

[*]: You can’t actually pass a ByteString into a compiled Script through the Plutus.V1.Ledger.Scripts API. Notice that you can only pass Data arguments using applyArguments. The Haskell synonym to Data is PAsData a (for any a), and PData.

Also see: Figuring out the representation of a Plutarch type.

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The isomorphism between makeIsDataIndexed, Haskell ADTs, and PIsDataRepr

When implementing PIsDataRepr for a Plutarch type, if the Plutarch type also has a Haskell synonym (e.g. ScriptContext is the Haskell synonym to PScriptContext) that uses makeIsDataIndexed - you must make sure the constructor ordering is correct.
README

Haskell synonym of Plutarch types
Prefer statically building constants

Whenever you can build a Plutarch constant out of a pure Haskell value - do it! Functions such as pconstant, phexByteStr operate on regular Haskell synonyms of Plutarch types. Unlike pcon, which potentially works on Plutarch terms (e.g. pcon $ PJust x, x is a Term s a). A Plutarch term is an entirely “runtime” concept. “Runtime” as in “Plutus Core Runtime”. They only get evaluated during runtime!
Plutarch Constants

If we know the desired value of a constant Term at compile-time, we can build the Term directly from Haskell synonyms. The function to do so is pconstant.
PConstant and PLift

These two closely tied together typeclasses establish a bridge between a Plutarch level type (that is represented as a builtin type, i.e. DefaultUni) and its corresponding Haskell synonym. The gory details of these two are not too useful to users, but you can read all about it if you want at Developers’ corner.
Concepts

Haskell synonym of Plutarch types