VIR Shell

An experiment, slow, everything might change, never use this

Try It

npx virsh

Goals

1. Scriptable and Bash-like for simple executions
2. Composable
3. Interoperable with JavaScript Promises
4. Optimized for small programs

TODOs

1. Error handling is terrible. Good luck. It's a combination of uncacught parser-errors, and my own errors thrown with very little context.
2. The grammar is overly-permissive. Some allowable stuff might be disallowed in future.
3. I want to add automatic semicolon insertion (ASI) as a pre-processing step.
4. Add currying, and auto-invocation e.g. ls = func { 12 }; ls #12

Simple Expressions

Numbers

10
12.0

Strings

"Hello"
'Hello'

Boolean

true
false

Lists

Lists are created implicly whenever a comma is used to separate values:

1, 2, 3

To create a 1-item list, use a trailing comma in parentheses (1,).

Grab a single item with [...] e.g.

l = 1, 2, 3;
l[0] == 1

Objects/Maps/Dicts

{
    name: "Foo",
    age: 19
}

Assignments

You do not need to declare variables. You just use them.

x = 10
y = "Hello"

Templates

Templates can use values from the current scope:

```
name = "Amber"
"Hello {name}"
```

Functions

Currently, you cannot define functions. You can call functions injected into your scope.

1. Call with a single arg.

   $ range 10
   [1, 2, 3, ..., 10]

2. You cannot invoke a function with zero args. You should instead return a calculated value.

3. Multiple args

   $ range 10 11
   [10, 11]

Generators

Iterations

For loops are not first-class constructs. They're just an remix of two primitives:

1. function evaluation
2. lazy/unbound function arguments

for i <- 1..10 {
    i
}

The { i } block is not bound, nor evaluated when it's passed as an argument to for. The invoked function is responsible for both binding the block to a Scope, and evaluating the body.

Conditionals

Lazy evaluation gives you branching without special constructs or callbacks. If statements will evaluate one, or another arguments depending on the conditional.

• Everything looks normal

  cond = true
  
  if cond {
      "True"
  } else {
      "False"
  }

• You can omit the else block:

  cond = true
  
  if cond {
      "True"
  } {
      "False"
  }

• You can omit the brackets too:

  cond = true
  
  if cond "True" "False"

User Defined Functions

Define user-defined functions with func

z = 1
y = func { x + z }

Call them with

y {x:2}
# 3

Under the hood, this is also a "hack". The defined function body is unbound and unevalated when the function is created. The body is evaluated when invoked later, but with a new scope.

The new scope is of a mix of the lexical scope when defined, and the dynamic scope when invoked. Calling y {x:1} causes any lexically bound x values to be shadowed by the dynamically bound x at call time. Since z is not shadowed, it resolves to 1.

Horrors

• with statements

  sc = {name: 'jay'};
  with sc {
      name
  }