Geist (German pronunciation: [ˈɡaɪst]) is a German word. Depending on context it can be translated as the English words mind, spirit, or ghost, covering the semantic field of these three English nouns.

-- https://en.wikipedia.org/wiki/Geist

The problem with most scripting languages is that they are not actually great programming languages.

But since they are convenient, quick to write, and have no compilation overhead, they get used.

Alot.

That's not a good thing.

Because: often times a script grows up and becomes a big ball of mud: a truly hard to maintain program.

Good testing and software engineering becomes really difficult, and one faces a full rewrite of the overgrown script in another language.

In really bad cases, I've seen shops expend years of effort by multiple people on such rewrites.

Ideally a script that has grown up should be re-written in a language with good tooling, static type checking, and good performance.

Geist puts forward this thesis: Why not write in that eventual language from the start?

The geist script-runner turns Go (golang) into a scripting language: the one you should write your scripts in from the start.

Geist makes it viable to write your scripts in Go, and then when they need to grow into actual programs, the transition is a seemless matter of adding a few lines of boilerplate to your script and moving it to a Go source heirarchy.

More: your configuration files can be written as geist. Go has fantastic support for declaring literal values, and this makes configuration easy. No more need to invent a new configuration file format for every new program.

Instead of inventing another scripting language, or another configuration format, geist offers a way to use Go as a scripting and configuration language from day one.

A geist script is #! runnable, there is no separate manual compilation step. Not even "go run" is needed on your part. Geist takes care of building and caching your script as an executable. You will need a go installation to get and build geist and geist-install, however once geist is installed by invoking geist-install, geist takes care of isolating itself from any other GOROOT or GOPATH.

The geist executable will read the geist script, and will add a couple of lines of boilerplate that turn it into a real Go program. e.g. geist adds the "package main" declaration, some imports, and wraps your lines in the main() function.

Then geist will compile and run it for you. The compilation actually only happens if the script has been changed (we cache the prior version); so geist offers even faster startup time than a "go run" invocation after the first compile.

Compilation happens in an isolated GOROOT/GOPATH environment under $HOME/.geist by default (settable with GEIST_HOME env variable). This means you can run geist starting in any directory, and it will ignore any other golang code, GOROOT/GOPATH settings.

A given geist script has an implicit main and package use is automatically detected to the extent possible (by goimports). "geist-install" acts as the "go install" replacement to install a new package under your ~/.geist/src heirarchy. The "geist-install" tool is used to initialize your $HOME/.geist directory as well. It need only be run once, without arguments, to do this.

Additional imports can be added anywhere, no problem. geist will collect them all to the top of the file before compiling it.

Natually structs and functions can be defined in a geist file, and the implicit main stops at the point of the first (if any) struct or fuction definition. the //endmain comment can also be used to terminate the automatically added main() function.

Planned additions:

• //include <path> will, in the future, be used to include additional geist (or .go) files from the main script. If the file is a .go file, then the package declaration will need to be removed and the imports merged.

• For configuration file support, and DSL replacement support, we'll want a means of including a user-defined and pre-defined set of functions/structs in the main package that all such local geist scripts should have access to.