perl6/step4_if_fn_do.pl

   1 use v6;
   2 use lib IO::Path.new($?FILE).dirname;
   3 use reader;
   4 use printer;
   5 use types;
   6 use env;
   7 use core;
   8
   9 sub read ($str) {
  10   return read_str($str);
  11 }
  12
  13 sub eval_ast ($ast, $env) {
  14   given $ast {
  15     when MalSymbol  { $env.get($ast.val) || die X::MalNotFound.new(name => $ast.val) }
  16     when MalList    { MalList([$ast.map({ eval($_, $env) })]) }
  17     when MalVector  { MalVector([$ast.map({ eval($_, $env) })]) }
  18     when MalHashMap { MalHashMap($ast.kv.map({ $^a => eval($^b, $env) }).Hash) }
  19     default         { $ast // $NIL }
  20   }
  21 }
  22
  23 sub eval ($ast, $env) {
  24   return eval_ast($ast, $env) if $ast !~~ MalList;
  25   return $ast if !$ast.elems;
  26
  27   my ($a0, $a1, $a2, $a3) = $ast.val;
  28   given $a0.val {
  29     when 'def!' {
  30       return $env.set($a1.val, eval($a2, $env));
  31     }
  32     when 'let*' {
  33       my $new_env = MalEnv.new($env);
  34       for |$a1.val -> $key, $value {
  35         $new_env.set($key.val, eval($value, $new_env));
  36       }
  37       return eval($a2, $new_env);
  38     }
  39     when 'do' {
  40       return eval_ast(MalList([$ast[1..*]]), $env)[*-1];
  41     }
  42     when 'if' {
  43       return eval($a1, $env) !~~ MalNil|MalFalse
  44         ?? return eval($a2, $env)
  45         !! return $a3 ?? eval($a3, $env) !! $NIL;
  46     }
  47     when 'fn*' {
  48       return MalCode(-> *@args {
  49         my @binds = $a1 ?? $a1.map(*.val) !! ();
  50         eval($a2, MalEnv.new($env, @binds, @args));
  51       });
  52     }
  53     default {
  54       my ($func, @args) = eval_ast($ast, $env).val;
  55       return $func.apply(|@args);
  56     }
  57   }
  58 }
  59
  60 sub print ($exp) {
  61   return pr_str($exp, True);
  62 }
  63
  64 my $repl_env = MalEnv.new;
  65
  66 sub rep ($str) {
  67   return print(eval(read($str), $repl_env));
  68 }
  69
  70 sub MAIN {
  71   $repl_env.set(.key, .value) for %core::ns;
  72   rep(q{(def! not (fn* (a) (if a false true)))});
  73
  74   while (my $line = prompt 'user> ').defined {
  75     say rep($line);
  76     CATCH {
  77       when X::MalException { .Str.say }
  78     }
  79   }
  80 }