Functions and Procedures¶
To promote reusability, readability and separation of code, Indigo supports functions and procedures. This chapter shows the syntax and expands on their usage.
This chapter's source file is
Functions.hs, that contains
module Indigo.Tutorial.Functions.Functions ( functionsContract ) where import Indigo data IncrementIf = IsZero Integer | HasDigitOne Natural deriving stock (Generic, Show) deriving anyclass (IsoValue) instance ParameterHasEntrypoints IncrementIf where type ParameterEntrypointsDerivation IncrementIf = EpdPlain functionsContract :: IndigoContract IncrementIf Natural functionsContract param = defContract do result <- case_ param $ ( #cIsZero #= checkZero , #cHasDigitOne #= checkHasDigitOne ) updateStorage result checkZero :: Var Integer -> IndigoFunction Bool checkZero val = defFunction do return (val == 0 int) checkHasDigitOne :: Var Natural -> IndigoFunction Bool checkHasDigitOne val = defFunction do base <- new$ 10 nat checkRes <- new$ False while (val > base && checkRes == False) do val =: val / base remainder <- new$ val % base checkRes =: remainder == 1 nat return checkRes updateStorage :: HasStorage Natural => Var Bool -> IndigoProcedure updateStorage result = defFunction do if result then storage =: 0 nat else incrementStorage incrementStorage :: HasStorage Natural => IndigoProcedure incrementStorage = defFunction do storage += 1 nat storage :: HasStorage Natural => Var Natural storage = storageVar
When converted to Michelson this program is equivalent to the
from the previous chapter.
The difference is fully visible, in that the contract itself is much easier to read because it has been broken down into simple functions.
Let's look at their definition, starting from the first one:
checkZero :: Var Integer -> IndigoFunction Bool checkZero val = defFunction do return (val == 0 int)
This function takes the place of the code-block we used to execute in the first
controlContract, that looked like this:
( #cIsZero #= \val -> do return (val == 0 int)
As you can see this is almost identical to the
checkZero function's code.
The main difference is that we put
val before an
= and used
this should be easy to figure out, because
defFunction is to functions what
defContract is to ... contracts, as you can see from the first lines here:
functionsContract param = defContract do checkZero val = defFunction do
The other difference is that by using functions we need to explicitly write a
signature, but this is not hard, we can see that the ones for
checkZero :: Var Integer -> IndigoFunction Bool
Just as we did in the Basics and Variables chapter for contracts, we can use a formula to make function signatures:
<function_name> :: [Var parameter ->] IndigoFunction <return_type>
Here's what you need to know:
- there can be 0 parameters as well as more than one.
- The return type can be any of the supported types.
In addition to this there are
IndigoProcedures, that are just like
IndigoFunctions, differing only by the absence of a return value (or in other
terms, they return
()) and in fact begin with the same
That's it, quite simple isn't it?
This file also contains examples of Indigo functions with no parameters
incrementStorage), multiple parameters (e.g.
that access the storage (e.g.
incrementStorage, note that just like
these need to specify the correct
You can define such Indigo functions and call them in different places, also note that just like the other imperative constructs they have (automatically managed) scope.
Now that we are armed with functions as well we can proceed to the next chapter: Side Effects and Errors.
Technical details: defFunction and defContract¶
IndigoFunctions are just
specialized versions of
These types are all connected and exist mostly for convenience. The same can be
defContract which is just a specialized version of
carries on all the required constraints.
defFunction is what makes this possible, as it adds scope management to the
IndigoM, using the same logic mentioned in the previous chapter
for imperative statements.
You can find the definitions for all of these types and functions in the