mal/io/step5_tco.io

MalTypes
MalReader

READ := method(str, MalReader read_str(str))

eval_ast := method(ast, env,
   (ast type) switch(
       "MalSymbol", env get(ast),
       "MalList", MalList with(ast map(a, EVAL(a, env))),
       "MalVector", MalVector with(ast map(a, EVAL(a, env))),
       "MalMap",
           m := MalMap clone
           ast foreach(k, v,
               keyObj := MalMap keyToObj(k)
               m atPut(MalMap objToKey(EVAL(keyObj, env)), EVAL(v, env))
           )
           m,
       ast
   )
)

EVAL := method(ast, env,
    loop(
        if(ast type != "MalList", return(eval_ast(ast, env)))
        if(ast isEmpty, return ast)
        if(ast at(0) type == "MalSymbol",
            ast at(0) val switch(
                "def!",
                    return(env set(ast at(1), EVAL(ast at(2), env))),
                "do",
                    eval_ast(ast slice(1,-1), env)
                    ast = ast last
                    continue, // TCO
                "if",
                    ast = if(EVAL(ast at(1), env), ast at(2), ast at(3))
                    continue, // TCO
                "fn*",
                    return(MalFunc with(ast at(2), ast at(1), env, block(a, EVAL(ast at(2), Env with(env, ast at(1), a))))),
                "let*",
                    letEnv := Env with(env)
                    varName := nil
                    ast at(1) foreach(i, e,
                        if(i % 2 == 0,
                            varName := e,
                            letEnv set(varName, EVAL(e, letEnv))
                        )
                    )
                    ast = ast at(2)
                    env = letEnv
                    continue // TCO
            )
        )

        // Apply
        el := eval_ast(ast, env)
        f := el at(0)
        args := el rest
        f type switch(
            "Block",
                return(f call(args)),
            "MalFunc",
                ast = f ast
                env = Env with(f env, f params, args)
                continue, // TCO
            Exception raise("Unknown function type")
        )
    )
)

PRINT := method(exp, exp malPrint(true))

RE := method(str, EVAL(READ(str), repl_env))

REP := method(str, PRINT(RE(str)))

repl_env := Env with(nil)
MalCore NS foreach(k, v, repl_env set(MalSymbol with(k), v))

// core.mal: defined using the language itself
RE("(def! not (fn* (a) (if a false true)))")

loop(
    line := MalReadline readLine("user> ")
    if(line isNil, break)
    if(line isEmpty, continue)
    e := try(REP(line) println)
    e catch(Exception,
        ("Error: " .. (e error)) println
    )
)