Alchemist - a non-deterministic esolang based on chemical reaction networks

Basics

A program consists of rules

A1 + ... + An -> B1 + ... Bm

There is a state called universe of atoms, if there are enough atoms of A1..An then such a rule is applicable. The program will start with some initial state and iterate indefinitely until no rules are applicable. From all the applicable rules a random one will be chosen and applied.

There are two special types of atoms which can only appear on the right hand side of a reaction:

• Out_"some string": Prints some string to stdout
• In_someAtom: Reads an integer from stdin and adds that many atoms of type someAtom

Regular atoms consist can only contain characters [0-9A-Za-z_].

Multiplicity

The atoms can have a number in front of them (eg. 2H + O -> H2O) which is short-hand for H + H + O -> H2O. This is the reason why atoms cannot start with a number.

One can also write a 0 in front of an atom which means the rule is only applicable if there is no such atom at all, this can be used for control-flow.

Initial Universe

The initial universe is either determined by user inputs, constant inputs or both:

• user inputs are given via the commandline when invoking the interpreter. The arguments are like the left hand-side of a rule (LHS), for example alchemist MyFantasticProgram.crn "101x + 3a" will use an initial universe with 3 a-atoms 101 xs. They can also be be separate arguments, so alchemist MyFantasticProgram.crn 101x 3a will do the same.
• constant inputs are given in the source code directely. These inputs are also of the form LHS and are specified after the rules, separated with a !

Usually these two will be merged, ie. the interpreter adds the numbers of the inputs of them, you can override the constant inputs completely by using the --override flag.

By default the universe will initially contain the atom _.

For more information, see the Examples.

Interpreter

bmo@Ooo % alchemist -h
usage: alchemist [-h] [-s SEED] (-e EXPR | FILE) INPUTS
  -e         --expression     evaluate expression
  -o         --override       override constant inputs (merges by default)
  -s SEED    --seed=SEED      set seed
  -d[LEVEL]  --debug[=LEVEL]  set debug level (0 to 2)
  -h         --help           print this help

Seeding

The SEED can be any string to achieve deterministic results, the program will print the used seed to stderr. For example:

seed: "1957628721 1"

If we now run alchemist -s "1957628721 1" Program.crn we will get the same results as in the previous run.

Debugging

Debug levels:

• 0: quiet; prints only the used seed
• 1: helpful; like 0 but also prints the remaining universe at the end
• 2: noisy; like 1 but also prints each applied rule