dsl-vs-sdf.md

Go+ ClassFile: DSL vs. SDF

Go+ doesn't support DSL (Domain Specific Language), but it's SDF (Specific Domain Friendly).

The Go+ philosophy of Domain is:

Don't define a language for specific domain.
Abstract domain knowledge for it.

Go+ introduces ClassFile to abstract domain knowledge.

NOTE: ClassFile is still in beta and may be subject to change.

What is ClassFile?

TODO

DEMO: Go+ DevOps Tools

This is a demo project to implement a new ClassFile work: github.com/xushiwei/gsh.

Before we dive into implementation of github.com/xushiwei/gsh, let's take a look how to use it.

First, let's create a new module named gshexample:

mkdir gshexample
cd gshexample
gop mod init gshexample

Second, get github.com/xushiwei/gsh into gshexample:

gop get github.com/xushiwei/gsh

Third, create a Go+ source file named ./example.gsh and write the following code:

mkdir "testgsh"

Fourth, run this project:

gop mod tidy
gop run .

It's strange to you that the file extension of Go+ source is not .gop but .gsh.

But the Go+ compiler can recognize .gsh files as Go+ source because github.com/xushiwei/gsh register .gsh as its ClassFile file extension.

We can change ./example.gsh more complicated:

type file struct {
	name  string
	fsize int
}

mkdir! "testgsh"

mkdir "testgsh2"
lastErr!

mkdir "testgsh3"
if lastErr != nil {
	panic lastErr
}

capout => { ls }
println output.fields

capout => { ls "-l" }
files := [file{flds[8], flds[4].int!} for e <- output.split("\n") if flds := e.fields; flds.len > 2]
println files

rmdir "testgsh", "testgsh2", "testgsh3"

Check last error

If we want to ensure mkdir successfully, there are three ways:

The simplest way is:

mkdir! "testsh"  # will panic if mkdir failed

The second way is:

mkdir "testsh"
lastErr!

Yes, github.com/xushiwei/gsh provides lastErr to check last error.

The third way is:

mkdir "testsh"
if lastErr != nil {
    panic lastErr
}

This is the most familiar way to Go developers.

Capture output of commands

And, github.com/xushiwei/gsh provides a way to capture output of commands:

capout => {
    ...
}

Similar to lastErr, the captured output result is saved to output.

For an example:

capout => { ls "-l" }
println output

Here is a possible output:

total 72
-rw-r--r--  1 xushiwei  staff  11357 Jun 19 00:20 LICENSE
-rw-r--r--  1 xushiwei  staff    127 Jun 19 10:00 README.md
-rw-r--r--  1 xushiwei  staff    365 Jun 19 00:25 example.gsh
-rw-r--r--  1 xushiwei  staff    126 Jun 19 09:33 go.mod
-rw-r--r--  1 xushiwei  staff    165 Jun 19 09:33 go.sum
-rw-r--r--  1 xushiwei  staff    110 Jun 19 09:33 gop.mod
-rw-r--r--  1 xushiwei  staff   1938 Jun 19 10:00 gop_autogen.go

We can use Go+ powerful built-in data processing capabilities to process captured output:

type file struct {
	name  string
	fsize int
}

files := [file{flds[8], flds[4].int!} for e <- output.split("\n") if flds := e.fields; flds.len > 2]

In this example, we split output by "\n", and for each entry e, split it by spaces (e.fields) and save into flds. Condition flds.len > 2 is to remove special line of output:

total 72

At last, pick file name and size of all selected entries and save into files.

Implementation of gsh

To most developers, they just use ClassFile. They don't need to implement a ClassFile project.

We provide a ClassFile template project: github.com/goplus/classfile-project-template.

TODO