From e9ff1c6fbbbac9ece2604876ab589ac282360446 Mon Sep 17 00:00:00 2001
From: Nicholas <nbnoll@eml.cc>
Date: Mon, 15 Nov 2021 15:08:03 -0800
Subject: Feat: added if/else branching and switch statement

Unsure about my modification to the language. I found the parsing of the
case body within switches to be odd - specifically that it parses
liberally and then checks that it has case -> cmd structuring while it
walks the code. This means the language is more permissive than the
semantics. I modified it to be more explicit, but at the cost of having
to end each case statement with a semicolon. I wanted a colon, but this
is a valid word character and thus will be lexed as part of the word.
---
 src/cmd/rc/code.c | 83 +++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 75 insertions(+), 8 deletions(-)

(limited to 'src/cmd/rc/code.c')

diff --git a/src/cmd/rc/code.c b/src/cmd/rc/code.c
index 786f284..7077a0e 100644
--- a/src/cmd/rc/code.c
+++ b/src/cmd/rc/code.c
@@ -38,12 +38,14 @@ storepc(int a)
     interpreter.code[a].i = interpreter.i;
 }
 
+void yyerror(const char *msg);
+
 static
 void
 walk(Tree *node)
 {
-    Tree *n;
-    int addr1, addr2;
+    Tree *n, *c;
+    int addr1, addr2, addr3;
 
     if(!node)
         return;
@@ -127,6 +129,7 @@ walk(Tree *node)
     case Tbang:
         walk(node->child[0]);
         emitf(Xbang);
+        break;
 
     case Tword:
         emitf(Xword);
@@ -164,17 +167,78 @@ walk(Tree *node)
         node = n;
         break;
     /* control structures */
+    case Tif:
+        walk(node->child[0]); // condition
+        emitf(Xtrue);
+        addr1 = emiti(0);
+        walk(node->child[1]); // if body
+        if(!node->child[2])   // no else
+            storepc(addr1);
+        else{
+            emitf(Xgoto);
+            addr2 = emiti(0);
+            storepc(addr1);
+            walk(node->child[2]);
+            storepc(addr2);
+        }
+        break;
+
+    case Tswitch:
+        /* NOTE:
+         * there are 3 addresses to store
+         * 1. addr1 = address to next case
+         * 2. addr2 = address to jump end instruction
+         * 3. addr3 = address of switch end
+         */
+        emitf(Xmark);
+        walk(node->child[0]); // word we match to
+        emitf(Xgoto);         // next case
+        addr1 = emiti(0);
+        addr2 = emitf(Xgoto); // switch end
+        addr3 = emiti(0); 
+        storepc(addr1);
+
+        // XXX: anyway to make this explicit in parser?
+        if(!(n = node->child[1]))
+            yyerror("empty switch statement");
+
+        emitcase:
+            if(!n)
+                goto donecase;
+            else if(n->type == ';'){
+                c = n->child[0];
+                n = n->child[1];
+            }else if(n->type == Tcase){
+                c = n;
+                n = nil;
+            }else
+                panicf("bad node type %d\n", n->type);
+
+            emitf(Xmark);
+            walk(c->child[0]);    // words
+            emitf(Xcase);
+            addr1 = emiti(0);     // next case
+            walk(c->child[1]);    // commands
+            emitf(Xgoto);
+            emiti(addr2);
+            storepc(addr1);
+
+            goto emitcase;
+        donecase:
+            storepc(addr3);
+        break;
+
     case Twhile:
-        addr1 = interpreter.i; // head of loop
+        addr1 = interpreter.i;     // head of loop
         walk(node->child[0]);
-        if(addr1 == interpreter.i)
-            fatal("TODO");
+        if(addr1 == interpreter.i) // empty condition => while(true)
+            emitf(Xsettrue);
         emitf(Xtrue);
-        addr2 = emiti(0); // goto end of loop
+        addr2 = emiti(0);          // goto end of loop
 
         walk(node->child[1]);
         emitf(Xgoto);
-        emiti(addr1);   // goto top of loop
+        emiti(addr1);              // goto top of loop
         storepc(addr2);
         break;
 
@@ -184,7 +248,10 @@ walk(Tree *node)
             walk(node->child[1]);
             // emitf(Xglob)
         }else{              // for(X)
-            fatal("TODO");
+            emitf(Xmark);
+            emitf(Xword);
+            emits(strdup("*"));
+            emitf(Xdollar);
         }
         emitf(Xmark); // null initial value for Xlocal
         emitf(Xmark);
-- 
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