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Declaring package requirements

Sometimes it may be desirable to use features from external packages in the definition of the workflow. For example, you may want to parse a configuration file with Guile DSV before even defining any processes. Or perhaps you may need to use an application to prepare state or query a database before the workflow is executed.

You can declare any package requirements with a require-packages form at the very top of your workflow file. This must be the first code expression after any commented lines. Before a workflow file is evaluated, the current environment is modified to make the specified packages available. Any specified Guile libraries are added to the load path, so care should be taken to ensure that the libraries are in fact compatible with the version of Guile used by the Workflow Language.

Scheme Procedure: require-packages package…

The require-packages procedure takes any number of package specifications. A package specification is the package name, optionally followed by @ and a version string. The Workflow Language guarantees that the declared packages will be available when the workflow file is evaluated.

;; Declare packages
require-packages
  . "guile-dsv"      ; for parsing CSV files
  . "guile-libyaml"  ; for parsing YAML files

;; Load them
import
  dsv
  yaml

;; Use them
define : load-config file
  if : file-exists? file
    read-yaml-file file
    error "Could not find configuration file!"
  …