Tempo Programming Language
Projection
Interact with host language

Interact with host language

Functions from the host language can be called from Tempo through interfaces.

hello.tempo
interface Printer {
  func Print(value: String);
}

func@(A,B) Hello(printA: Printer@A, printB: Printer@B) {
  printA.Print("Hello from A");
  printB.Print("Hello from B");
}

Now project the choreography by executing the following command. A new file called hello.go will be generated with the Go projections of the choreography.

Terminal
$ tempo build --package main hello.tempo > hello.go

Create a main.go file with the following contents. When you instantiate the projection, you provide an implementation of the interface.

main.go
package main

import (
  "fmt"

  "github.com/tempo-lang/tempo/runtime"
  "github.com/tempo-lang/tempo/simulator"
)

// define printer struct that implements the Printer interface
type PrinterImpl struct{}
func (p *PrinterImpl) Print(env *runtime.Env, value string) {
  fmt.Printf("%s\n", value)
}

func main() {
  simulator.Run(
    simulator.Proc("A", func(env *runtime.Env) any {
      // provide printer implementation
      Hello_A(env, &PrinterImpl{})
      return nil
    }),
    simulator.Proc("B", func(env *runtime.Env) any {
      // provide printer implementation
      Hello_B(env, &PrinterImpl{})
      return nil
    }),
  )
}

Now run the following commands to download dependencies, build, and run the example

Terminal
$ go mod init example    # create go module
$ go mod tidy            # download dependencies
$ go run .               # build and run it

You should see that it prints out the following two lines, but since the two processes run concurrently the lines may come in any order.

Hello from A
Hello from B
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