mal/perl6/step5_tco.pl

use v6;
use lib IO::Path.new($?FILE).dirname;
use reader;
use printer;
use types;
use env;
use core;

sub read ($str) {
  return read_str($str);
}

sub eval_ast ($ast, $env) {
  given $ast {
    when MalSymbol  { $env.get($ast.val) || die X::MalNotFound.new(name => $ast.val) }
    when MalList    { MalList([$ast.map({ eval($_, $env) })]) }
    when MalVector  { MalVector([$ast.map({ eval($_, $env) })]) }
    when MalHashMap { MalHashMap($ast.kv.map({ $^a => eval($^b, $env) }).Hash) }
    default         { $ast // $NIL }
  }
}

sub eval ($ast is copy, $env is copy) {
  loop {
    return eval_ast($ast, $env) if $ast !~~ MalList;
    return $ast if !$ast.elems;

    my ($a0, $a1, $a2, $a3) = $ast.val;
    given $a0.val {
      when 'def!' {
        return $env.set($a1.val, eval($a2, $env));
      }
      when 'let*' {
        my $new_env = MalEnv.new($env);
        for |$a1.val -> $key, $value {
          $new_env.set($key.val, eval($value, $new_env));
        }
        $env = $new_env;
        $ast = $a2;
      }
      when 'do' {
        eval_ast(MalList([$ast[1..*-2]]), $env);
        $ast = $ast[*-1];
      }
      when 'if' {
        if eval($a1, $env) ~~ MalNil|MalFalse {
          return $NIL if $a3 ~~ $NIL;
          $ast = $a3;
        }
        else {
          $ast = $a2;
        }
      }
      when 'fn*' {
        my @binds = $a1 ?? $a1.map(*.val) !! ();
        my &fn = -> *@args {
          eval($a2, MalEnv.new($env, @binds, @args));
        };
        return MalFunction($a2, $env, @binds, &fn);
      }
      default {
        my ($func, @args) = eval_ast($ast, $env).val;
        return $func.apply(|@args) if $func !~~ MalFunction;
        $ast = $func.ast;
        $env = MalEnv.new($func.env, $func.params, @args);
      }
    }
  }
}

sub print ($exp) {
  return pr_str($exp, True);
}

my $repl_env = MalEnv.new;

sub rep ($str) {
  return print(eval(read($str), $repl_env));
}

sub MAIN {
  $repl_env.set(.key, .value) for %core::ns;
  rep(q{(def! not (fn* (a) (if a false true)))});

  while (my $line = prompt 'user> ').defined {
    say rep($line);
    CATCH {
      when X::MalException { .Str.say }
    }
  }
}