mers/mers

mers

Mers is a high-level programming language. It is designed to be safe (it doesn't crash at runtime) and as simple as possible.

Install from crates.io:

cargo install mers

See also: Quickstart

what makes it special

Simplicity

Mers is simple. There are only few expressions:

• Values (1, "my string", ...)
• Blocks ({})
• Tuples (()) and Objects ({})
• Assignments (=)
• Variable initializations (:=)
• Variables (my_var, &my_var)
• If statements (if <condition> <then> [else <else>])
• Functions (arg -> <do something>)
• Function calls arg.function or arg1.function(arg2, arg3) (= (arg1, arg2, arg3).function)

Everything else is implemented as a function.

Types and Safety

Mers is built around a type-system where a value could be one of multiple types.

x := if condition { 12 } else { "something went wrong" }

In mers, the compiler tracks all the types in your program, and it will catch every possible crash before the program even runs: If we tried to use x as an int, the compiler would complain since it might be a string, so this does not compile:

list := (1, 2, if true 3 else "not an int")
list.sum.println

Type-safety for functions is different from what you might expect. You don't need to tell mers what type your function's argument has - you just use it however you want as if mers was a dynamically typed language:

sum_doubled := iter -> {
  one := iter.sum
  (one, one).sum
}
(1, 2, 3).sum_doubled.println

We could try to use the function improperly by passing a string instead of an int:

(1, 2, "3").sum_doubled.println

But mers will catch this and show an error, because the call to sum inside of sum_doubled would fail.

Error Handling

Errors in mers are normal values. For example, ("ls", ("/")).run_command has the return type ({Int/()}, String, String)/RunCommandError. This means it either returns the result of the command (exit code, stdout, stderr) or an error (a value of type RunCommandError).

So, if we want to print the programs stdout, we could try

(s, stdout, stderr) := ("ls", ("/")).run_command
stdout.println

But if we encountered a RunCommandError, mers wouldn't be able to assign the value to (s, stdout, stderr), so this doesn't compile. Instead, we need to handle the error case, using the try function:

("ls", ("/")).run_command.try((
  (s, stdout, stderr) -> stdout.println,
  error -> error.println,
))

docs

docs will be available in some time. for now, check mers_lib/src/program/configs/*