Soul
| Paradigm(s) | concatenative |
|---|---|
| Designed by | Marco Devillers |
| Appeared in | 2022 |
| Type system | dynamic |
| Memory system | stack |
| Computational class | Turing complete |
| Reference implementation | https://github.com/egel-lang/soul |
| File extension(s) | .soul |
Soul is an esoteric concatenative one-stack language, a small explorative language with an interpreter written in a day. Most concatenative languages work on a state, often that's another stack. For example, Forth has a data and return stack and Postscript has an extra stack outputting to a page.
Soul is a minimalist language that provides one thing, and one thing only, the one sole stack. That, of course, is very problematic as a model of computation but Soul gets around that with two tricks:
1. Treat the stack as random access memory.
2. Whenever a constant integer or text is found on top of the stack, that gets swapped with whatever is underneath.
Soul expressions consist of integers, texts, and words. Words may define other expressions. A Soul expression defines a stack. The top of the stack is repeatedly evaluated until the stack is empty.
Predefined Operators
fetch, put, and delete inspect or modify the stack, they all
take an integer argument where put takes a second argument to put somewhere
in the stack.
The arithmetic operators +, -, *, / are all binary prefix
operators. + is overloaded to work on texts also.
The equality operator = tests two arguments for equivalence, it
results in either true or false. Both booleans are functions
that select between two arguments; e.g., true f g evaluates to
f.
print and line are the basic input/output words. to_int and
to_text convert between integers and texts.
Examples
Hello World example:
"hello" print "world" print
Output 42, showcasing the defintion of a word:
# calculate the answer to everything :f * 6 + 3 4 f print
The faculty function:
# the faculty function # get :get2 delete 1 :get1 fetch 5 + 3 delete get2 :get0 fetch 4 + 4 fetch get2 :get fetch 2 get0 get1 # fac :fac3 get 2 fac * :fac2 fetch 3 - 1 fac3 :fac1 delete 1 1 :fac0 get 4 = 0 fac1 fac2 :fac fetch 1 fac0 fac 6 print
The Soul interpreter is written as an Egel script and implements a REPL.