Execute expressions properly

This way we can actually capture their execution status

lib/IUtils/Compiler.rakumod

@@ -52,6 +52,21 @@ class IdrisError is Exception {
     }
 }
 
+#| An error coming from a compiled expression
+class ExpressionError is Exception {
+    has Str $.out;
+    has Str $.err;
+    has Int $.exit-code;
+    has Str $.expr;
+
+    method message {
+        qq:to/END/;
+        Error running expression: $.expr
+        Command exited with $.exit-code
+        END
+    }
+}
+
 #| Invoke an idris command
 sub idris-run(*@cmd) is export {
     my $proc = run "idris2",  @cmd, :out, :err;
@@ -69,5 +84,17 @@ sub idris-run(*@cmd) is export {
 # TODO: Special handling for IO Bool to make this eaiser
 #| Exec the expression with the given name in the given file
 sub idris-exec($expr, $file) is export {
-    idris-run '--find-ipkg', '--exec', $expr, $file
+    # Have idris compile an executable for the expression,
+    idris-run '--find-ipkg', '--client', ":c iutils_out $expr", $file;
+    # Run the expression
+    my $proc = run 'build/exec/iutils_out', :out, :err;
+    my $out = $proc.out.slurp(:close);
+    my $err = $proc.err.slurp(:close);
+    unless $proc {
+        ExpressionError.new(
+            out => $out, err => $err,
+            exit-code => $proc.exitcode, expr => $expr
+        ).throw;
+    }
+    return $out;
 }