Perl: add step2_eval.

1 files changed, 80 insertions, 0 deletions

diff --git a/perl/step2_eval.pl b/perl/step2_eval.pl
new file mode 100644
index 0000000..c3910bd
--- /dev/null
+++ b/perl/step2_eval.pl
@@ -0,0 +1,80 @@
+use strict;
+use warnings;
+use readline qw(readline);
+use feature qw(switch);
+use Data::Dumper;
+
+use reader;
+use printer;
+
+# read
+sub READ {
+    my $str = shift;
+    return reader::read_str($str);
+}
+
+# eval
+sub eval_ast {
+    my($ast, $env) = @_;
+    given (ref $ast) {
+        when (/^Symbol/) {
+            if (exists $env->{$$ast}) {
+                return $env->{$$ast};
+            } else {
+                die "'" . $$ast . "' not found";
+            }
+        }
+        when (/^List/) {
+            my @lst = map {EVAL($_, $env)} @$ast;
+            return List->new(\@lst);
+        }
+        default {
+            return $ast;
+        }
+    }
+}
+
+sub EVAL {
+    my($ast, $env) = @_;
+    #print "EVAL: " . printer::_pr_str($ast) . "\n";
+    if (! ((ref $ast) =~ /^List/)) {
+        return eval_ast($ast, $env);
+    }
+
+    # apply list
+    my $el = eval_ast($ast, $env);
+    my $f = $el->[0];
+    return &{ $f }($el->rest());
+}
+
+# print
+sub PRINT {
+    my $exp = shift;
+    return printer::_pr_str($exp);
+}
+
+# repl
+my $repl_env = {};
+sub REP {
+    my $str = shift;
+    return PRINT(EVAL(READ($str), $repl_env));
+}
+
+$repl_env->{'+'} = sub { Integer->new(${$_[0][0]} + ${$_[0][1]}) };
+$repl_env->{'-'} = sub { Integer->new(${$_[0][0]} - ${$_[0][1]}) };
+$repl_env->{'*'} = sub { Integer->new(${$_[0][0]} * ${$_[0][1]}) };
+$repl_env->{'/'} = sub { Integer->new(${$_[0][0]} / ${$_[0][1]}) };
+
+while (1) {
+    my $line = readline("user> ");
+    if (! defined $line) { last; }
+    eval {
+        use autodie; # always "throw" errors
+        print(REP($line), "\n");
+        1;
+    }; 
+    if (my $err = $@) {
+        chomp $err;
+        print "Error: $err\n";
+    }
+}