#when

1 files changed, 27 insertions, 0 deletions

diff --git a/bootstrap/parse.c b/bootstrap/parse.c
index 0d9ab16..1848caf 100644
--- a/bootstrap/parse.c
+++ b/bootstrap/parse.c
@@ -394,6 +394,8 @@ lex(struct parser *P) {
          tok.t = '##';
       } else if (!strcmp(s, "#len")) {
          tok.t = '#len';
+      } else if (!strcmp(s, "#when")) {
+         tok.t = TKhwhen;
       } else if (!strcmp(s, "#tag")) {
          tok.t = '#tag';
       } else if (!strcmp(s, "#?")) {
@@ -3073,6 +3075,31 @@ parsedecl(decl_yielder_t yield, void *yarg, struct parser *P, bool toplevel) {
    struct attr attr = {0};
    decl.container = P->container;
 
+   while (lexmatch(P, &tok, TKhwhen)) {
+      struct expr test = parseexpr(P);
+      if (!fold(&test) || test.ty->t != TYbool)
+         fatal(P, test.span, "#when test is not a constant bool expression");
+      assert(test.t == Eboolit);
+      lexexpect(P, '{');
+      if (test.i) {
+         while (!lexmatch(P, &tok, '}'))
+            parsedecl(yield, yarg, P, toplevel);
+      } else {
+         int pabal = 0, // ( ) parens balance
+             bkbal = 0, // [ ] brackets ..
+             bcbal = 1; // { } braces ..
+
+         while (pabal || bkbal || bcbal) { 
+            tok = lex(P);
+            switch (tok.t) {
+            case '[': ++bkbal; break; case ']': --bkbal; break;
+            case '{': ++bcbal; break; case '}': --bcbal; break;
+            case '(': ++pabal; break; case ')': --pabal; break;
+            }
+         }
+      }
+   }
+
    if (lexmatch(P, &tok, '#')) {
       lexexpect(P, '[');
       while (!lexmatch(P, NULL, ']')) {