Documentation

Blan is a custom tree-walking interpreter built around Hindi slang. It was written as an applied exercise in compiler design — specifically the Lexical Analysis, Syntax Analysis, and Semantic Analysis phases from the CS312 curriculum at RGIPT.

The compiler is implemented in C++17. The backend execution layer is written in Go and handles asynchronous job execution, result caching via a custom LSM-tree engine (StrataKV), and JWT-based authentication.

This playground sends your source code to the Go backend, which hashes it, checks the cache, and either returns a cached result immediately or runs it through the C++ binary via a bounded worker pool.

Every Blan program must begin with the entry marker and end with the exit marker. Tokens found after the exit marker produce a syntax error.

Haan Meri Jaan
// your program goes here
Bhag Bsdk

Single-line comments are supported with // and are ignored by the lexer.

Variables are declared and assigned in a single statement using bhadwa and matlb. There is no separate declaration without assignment.

bhadwa x matlb 10
bhadwa name matlb "Aditya"
bhadwa flag matlb sach

Reassignment uses the same syntax. There is no mutation keyword — bhadwa is always used.

bhadwa count matlb 5
bhadwa count matlb count - 1

The evaluator uses a std::variant-based Value type that holds one of four kinds at runtime.

bhadwa x matlb 42
bhadwa y matlb x + 8

bhadwa greeting matlb "Haan "
bolna greeting + "Meri Jaan"

bolna sach        // prints: sach
bolna sach == 1   // prints: sach
bolna !jhooth     // prints: sach

Operators are evaluated left to right within each precedence level. The full precedence chain from lowest to highest:

||  →  &&  →  == !=  →  < <= > >=  →  + -  →  * / %  →  - ! (unary)

Type mismatches produce a runtime error. You cannot subtract strings or apply ! to a number.

Conditionals use agar for if, warna for else-if, nahi_toh for else, and khtm to close the block. The tab keyword closes the condition header.

agar x > 15 tab
    bolna "greater"
warna x == 10 tab
    bolna "exactly ten"
nahi_toh
    bolna "less"
khtm

The warna chain is handled recursively by the parser — you can nest as many else-if branches as needed. The khtm keyword always appears exactly once, closing the entire chain.

Legacy aliases warna_agar and nhi_toh are still accepted for backward compatibility.

The while loop uses JabTak to open, TabTak to close the condition header, and hogya to end the body.

bhadwa count matlb 3

JabTak count > 0 TabTak
    bolna count
    bhadwa count matlb count - 1
hogya

The evaluator enforces a hard iteration cap of 100,000 loops. Programs that exceed this are terminated with a runtime error to prevent infinite loops from hanging the execution worker.

Blan uses themed error messages. They are not meant to be polite.