Marcel is a shell. The main idea is to rely on piping as the primary means of composition, as with any Unix or Linux shell. However, instead of passing strings from one command to the next, marcel passes Python values: builtin types such as lists, tuples, strings, and numbers; but also objects representing files and processes.
Linux has extremely powerful commands such as awk and find. Most people know how to do a few simple operations using these commands. But it is not easy to exploit the full power of these commands due to their reliance on extensive "sub-languages" which do:
Filtering: What data is of interest?
Processing: What should be done with the data?
Formatting: How should results be presented?
By contrast, if you know Python, then you already know the language used by marcel. You use marcel operators combined with Python code to filter data, process it, and control command output.
The commands and syntax supported by a shell constitute a language which can be used to create scripts. Of course, in creating a script, you rely on language features that you typically do not use interactively: control structures, data types, and abstraction mechanisms (e.g. functions), for example. Viewed as a programming language, shell scripting languages are notoriously bad. I didn't think it was wise to bring another one into the world. So marcel takes a different approach, using
Python as a scripting language.