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This project contains tools for shrinking plutus scripts.
For plutus TX Shrinker is still somewhat experimental. You can use either Shrink.PlutusTX.shrinkCompiled or Shrink.PlutusTXTH.shrinkCompiledTH, both of which require you build shrinker-tx from the ./shrinker-tx directory. Shrink can be fairly slow on large scripts, hopefully this will improve with further development, but with plutustx there also seem to be laziness issues where shrink will run on the same script many times causing it to be much slower.
In most other cases Shrink.shrinkScript is the only function you need. If you want to exclude particular tactics perhaps because they are slow or have a bug you can use shrinkScriptSp (withoutTactics ["curry"]) scriptYouWantToShrink .
If you find a bug please report it on github or email me at [email protected], a print of the uplc fed to shrink would be much appreciated. Feature requests and suggestions are also welcome.
Shrinker uses a number of tactics which make small changes to code which may reduce the size and runs a search keeping track of the smallest scripts produced by these tactics until nothing smaller is found.
Subs applies a beta-reduction, this often corresponds to inlining a function and can reduce script size if the function is only used once.
Curry currys a function.
Weak unsubs finds an expression which appears at least twice and undoes a beta-reduction. This often corresponds to common sub expression elimination.
Strong unsubs is a more general version of weak unsubs, it also corresponds to undoing beta-reductions but it invents a lambda function in order to make the reductions possible.
ie. ((2 + 1) + (3 + 1)) might reduce to (\f -> f 2 + f 3)(\x -> x + 1)
Remove dead code looks for beta reductions where the variable bound by the lambda is not referenced, or where the argument is another variable. In either case the reduction always makes the code smaller so it's separated from Subs for performance.
Clean Pairs is a simple tactic required to make currying useful.
It reduces fst (x,_) to x and fst (_,y) to y. It's required to make currying useful.
Clean Force Delay is a simple tactic that removes delays which are imediately forced.
ie !#() becomes () to use pluto syntax.
Promote Errors looks for terms which will always error and replaces them with Error.
ie 1 + Error becomes Error