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Creating programs from Markdown code blocks

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README.md

literate-programming

Write your code anywhere and in any order with as much explanation as you like. literate-programming will weave it all together to produce your project.

This is a modificaiton of and an implementation of Knuth's Literate Programming technique. It is perhaps most in line with noweb.

It uses markdown as the basic document format with the code to be weaved together being delimited by each line having 4 spaces as is typical for markdown. Note that it requires spaces but not tabs. This allows one to use tabs for non lit pro code blocks as well as paragraphs within lists. GitHub flavored code fences can also be used to demarcate code blocks.

It can handle any programming language, but has some standard commands useful for creating HTML, CSS, and JavaScript.

Installation

This requires node.js and npm to be installed. Then issue the command:

npm install -g literate-programming

Using

From the command line:

literate-programming <file.md>

This will process the literate program in file.md and produce whatever output files are specified in the literate program.

Use literate-programming -h for command flag usage, including specifying the root output directory.

It can also be used as an executable program; see primes.md for an example program of this kind.

Example

Let's give a quick example. Here is the text of sample.md

# Welcome

So you want to make a literate program? Let's have a program that outputs
all numbers between 1 to 10.

Let's save it in file count.js

[count.js](#Structure "save:")

## Structure 

We have some intial setup. Then we will generate the array of numbers. We
end with outputting the numbers. 

    var numarr = [], start=1, end = 11, step = 1;

    _"Loop"

    _"Output"

## Output 

At this point, we have the array of numbers. Now we can join them with a
comma and output that to the console.

    console.log("The numbers are: ", numarr.join(", ") );

## Loop

Set the loop up and push the numbers onto it. 

    var i;
    for (i = start; i < end; i += step) {
        numarr.push(i);
    }

And it can be run from the command line using node count.js

There are more examples, but for a non-trivial example, see the literate program that compiles to literate-programming.

Document syntax

A literate program is a markdown document with some special conventions.

The basic idea is that each header line (regardless of level, either atx # or seText underline ) demarcates a full block. Code blocks within a full block are the bits that are woven together.

Code Block

Each code block can contain whatever kind of code, but there are three special syntaxes:

  1. _"Block name" This tells the compiler to compile the block with "Block name" and then replace the _"Block name" with that code.
  2. _`javascript code` One can execute arbitrary javascript code within the backticks, but the parser limits what can be in there to one line.
  3. MACROS all caps are for constants or macro functions that insert their output in place of the caps. Note that if you have MACRO(_"something") then the current version does not parse _"something" as a code block. This will hopefully get fixed along with being able to use code blocks in commands. This applies even if MACRO does not match so it is a bug, not a feature :( To fix this, put a space between MACRO and the parenthesis.

For both 1 and 3, if there is no match, then the text is unchanged. One can have more than one underscore for 1 and 2; this delays the substitution until another loop. It allows for the mixing of various markup languages and different processing points in the life cycle of compilation. See logs.md for an example.

Directive

A directive is a command that interacts with external input/output. Just about every literate program has at least one save directive that will save some compiled block to a file.

The syntax for the save directive is

[file.ext](#name-the-heading "save: named code block | pipe commands")  

where file.ext is the name of the file to save to, name-the-heading is the heading of the block whose compiled version is being saved (spaces in the heading get converted to dashes for id linking purposes), save: is the directive to save a file, named code block is the (generally not needed) name of the code block within the heading block, and the pipe commands are optional as well for further processing of the text before saving.

For other directives, what the various parts mean depends, but it is always

[some](#stuff "dir: whatever")  

where the dir should be replaced with a directive name.

Pipes

One can also use pipes to pipe the compiled text through a command to do something to it. For example, _"Some JS code | jshint" will take the code in block some JS code and pipe it into jshint to check for errors; it will report the errors to the console. We can also use pipe commands in a save directive: FILE "Some JS code" code.js | jstidy will tidy up the code before storing it in the file code.js.

Named Code Block

Finally, you can use distinct code blocks within a full block.

Start a line with link syntax that does not match a directive. Then it will create a new code block with the following data [code name](#link "type | pipes"). All parts are optional. The link is not used and can be anything. The minimum is [](#) to make a new (unnamed) code block.

Example: Let's say in heading block Loopy we have [outer loop](# "js") at the start of a line. Then it will create a code block that can be referenced by _"Loopy:outer loop".

Nifty parts of writing literate programming

  • You can have your code in any order you wish.
  • You can separate out flow control from the processing. For example,

    if (condition) {
        _"Truth"
    } else {
        _"Beauty"
    }
    

    The above lets you write the if/else statement with its logic and put the code in the code blocks truth and beauty. This can help keep one's code to within a single screenful per notion.

  • You can write code in the currently live document that has no effect, put in ideas in the future, etc. Only those on a compile path will be seen.
  • You can "paste" multiple blocks of code using the same block name. This is like DRY, but the code does get repeated for the computer. You can also substitute in various values in the substitution process so that code blocks that are almost the same but with different names can come from the same root structure.
  • You can put distracting data checks/sanitation/transformations into another block and focus on the algorithm without the use of functions (which can be distracting).
  • You can use JavaScript to script out the compilation of documents, a hybrid of static and dynamic.

I also like to use it to compile an entire project from a single file, pulling in other literate program files as needed. That is, one can have a command-and-control literate program file and a bunch of separate files for separate concerns. But note that you need not split the project into any pre-defined ways. For example, if designing a web interface, you can organize the files by widgets, mixing in HTML, CSS, and JS in a single file whose purpose is clear. Then the central file can pull it all in to a single web page (or many).

LICENSE

MIT-LICENSE

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