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

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

→ 3

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

→ 1

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

→ prints: result = 2
→ returns: 2

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

→ 3

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;')

Runtime code is under src/ (lexer/, compiler/, runtime/, debug/). Tests are in test/.

Plan

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