langsagne

Minimal programming language parser and execution experiment

Play

bun run test
bun run exec examples/assignment
bun run exec -- --trace examples/loop
bun run exec -- --step examples/if-else

Programs live in examples/. Use Enter or n for next, p for previous, and q to quit in step mode.

Language

Syntax

• numbers: 1, 42
• strings: "hello", 'path/to/file'
• variables: a, count_1
• assignment: a = 1 + 2
• arithmetic: +, -, *, / (numeric only)
• comparison: < (returns 1 or 0)
• parentheses: (1 + 2) * 3
• blocks: { ... }
• if (expr) { ... } else { ... }
• while (expr) { ... }
• fn name(a, b) { ... }
• return expr;
• function calls: add(1, 2)
• statements end with ;
• last expression value is the program result

Not supported yet: string +, ==, arrays, comments, forward references.

System calls

Call	Args	Result
print(...)	zero or more expressions	prints to stdout, leaves last arg in ax
assert(expr)	one expression	throws if falsy
clock()	none	Date.now()

Functions must be declared before use. Calls check arity (add(1) is an error).

Examples

Assignment and arithmetic

a = 1;
b = 2 + a;
b;

→ 3

Loop

i = 0;
sum = 0;
while (i < 2) {
  sum = sum + i;
  i = i + 1;
}
sum;

→ 1

If / else and multi-arg print

value = 0;
if (value) {
  result = 1;
} else {
  result = 2;
}
print('result =', result);
result;

→ prints: result = 2
→ returns: 2

Functions

fn add(a, b) {
  return a + b;
}
add(1, 2);

→ 3

Failed assertion

assert(1);
assert(1 + 2 < 4);
assert(2 + 2 < 4);

→ RUNTIME ERR: assert failed
   at line 3

API

import { execute } from './src/index.ts'

execute('a = 1; b = a + 2; b;') // 3

execute(code) compiles and runs source, then returns the final value in ax.

For directive-level debugging:

import { inspect } from './src/index.ts'

const { directives, trace, result } = inspect('a = 1; a;')

The four phase entry points are src/tokenize.ts, src/parse.ts, src/run.ts, and src/trace.ts. Each call owns its state. Tests are in test/.

Plan

See docs/design.md for the current gaps between this project and the c4-inspired language target.