waterworks is a library for building pipelines of chained computations, with a focus on being explicit about opting in as a stage of a given pipeline and for a quick and convenient way of inspecting the output of each stage and acting on that output to potentially terminate the pipeline early.

It was designed to be used for the flow of data in a compiler, and is put to "production" use in my personal compiler project, catastrophic.

Usage of waterworks first requires defining the individual stages that the overall computation pipeline will be put together with.

A stage is defined by the Error type global to the pipeline, the input and output of that specific stage, and the run method for performing the actual computation.

For example, if we were constructing a compiler we might have an initial file parsing stage like so:

struct FileParseStage;

impl Stage<CompileError> for FileParseStage {
    type Input = PathBuf;
    type Output = Ast;

    fn run(self, input: PathBuf) -> Result<Ast, CompileError> {
        parse_file(input)
    }
}

This can then be put together into a full pipleine, chained into adsitional compilation stages:

let pipe = pipeline(FileParseStage, |_| ())
    .and_then(AstAnalysisStage, |_| ())
    .and_then(OptimisationStage, |_| ())
    .and_then(ComppilationStage, |_| ());

The pipeline construction and chaining methods both take a callback in addition to the stage being attached to the pipeline. This callback can be used to both inspect the result of the associated stage and to terminate the execution of the pipeline early.

For example, say you wanted a compiler flag that simply logged the output of the parser and then returned - you could implement that with the following callback when attaching the FileParseStage above:

|ast| if log_ast {
    println!("{:?}", ast);
    Continue::Cancel
} else {
    Continue::Continue
}

For convenience in trivial cases, a ()-returning closure is treated as if it was explicitly returning Continue::Continue

To then run a pipeline, it's a simple case of calling run, passing in the first stage's defined input. This will then return a result of either the output of the final stage in the pipeline, the first error that gets returned by a stage, or whether the pipeline was cancelled early.

let result = pipe.run("waterworks.rs");