jitcalc

jitcalc is a calculator written in the V programming language.

What's special about it?

After parsing the input expression and generating a syntax tree, it does something different. Instead of traversing the tree interpreting the final solution, it creates a x86_64 program just in time and executes it, generating the answer.

After each line a hexdump and x86_64 assembly instructions are listed on the left. Use the ast command to toggle dumping the expression's AST alongside it.

Variables can be declared and assigned, and are preserved between expressions. Use the reset command to reset the symbol table.

Want to read more? Check out the article on l-m.dev here!

code

Constituting for about 93 lines of the program, code generation is incredibly simple. By calling the gen() function recursively over an entire expression tree, machine code can be generated.

type Symtable = map[string]&Box[i64]

fn gen(node &Expr, mut prg JitProgram, mut symtable Symtable)!

About 64 lines, parsing is just as simple. Using a recursive pratt parser it can generate a syntax tree.

struct Expr {
	lhs &Expr = unsafe { nil }
	rhs &Expr = unsafe { nil }
	op  Op
	val string
}

fn expr(mut l Lexer, min_bp int) !&Expr

49 lines, the lexer is efficient. It has the ability to look ahead by one token and is called by the parser constantly requesting tokens.

enum Op { eof uneg ident assign obr cbr num add sub mul div mod }

struct Lexer {
	line string
mut:
	pos int
	tok Op
	tok_lit string
	peek Op
	peek_lit string
}

fn (mut l Lexer) next() !Op