kern: np: Add support for return statements

This commit introduces lexical, parsing and code generation support for
the return statements. As of now, one is only able to return unsigned integers
but this will be expanded upon in the future

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 41 insertions, 1 deletions

diff --git a/src/sys/np/core/np_lex.c b/src/sys/np/core/np_lex.c
index 389f1e2..222feba 100644
--- a/src/sys/np/core/np_lex.c
+++ b/src/sys/np/core/np_lex.c
@@ -144,6 +144,11 @@ static int
 lex_cmptok(char *tokstr, struct lex_token *res)
 {
     switch (*tokstr) {
+    case 'r':
+        if (strcmp(tokstr, TOKEN_RETURN) == 0) {
+            res->token = TT_RETURN;
+        }
+        return 0;
     case 'b':
         if (strcmp(tokstr, TOKEN_BEGIN) == 0) {
             res->token = TT_BEGIN;
diff --git a/src/sys/np/core/np_parse.c b/src/sys/np/core/np_parse.c
index 4119d8b..b7b854b 100644
--- a/src/sys/np/core/np_parse.c
+++ b/src/sys/np/core/np_parse.c
@@ -84,7 +84,8 @@ static const char *stoktab[] = {
     /* Keywords */
     [TT_BEGIN]  = "<TT_BEGIN>",
     [TT_PROC]   = "<TT_PROC>",
-    [TT_END]    = "<TT_END>"
+    [TT_END]    = "<TT_END>",
+    [TT_RETURN] = "<TT_RETURN>"
 };
 
 /*
@@ -173,6 +174,35 @@ parse_type(struct np_work *work, struct lex_token *tok)
 }
 
 /*
+ * Parse a return statement
+ *
+ * @work: Input work
+ * @tok: Current token
+ *
+ * Returns zero on success
+ */
+static int
+parse_return(struct np_work *work, struct lex_token *tok)
+{
+    tt_t tt;
+
+    /*
+     * For now we'll only accept numbers as return values
+     * so we must see one after the return statement
+     */
+    tt = parse_expect(work, "return", TT_NUMBER, tok);
+    if (tt == TT_NONE) {
+        return -1;
+    }
+
+#define PIIR_PUSH(BYTE) piir_push(work->piir_stack, (BYTE))
+    PIIR_PUSH(PIIR_RET_NUM);
+    PIIR_PUSH(tok->val);
+#undef PIIR_PUSH
+    return 0;
+}
+
+/*
  * Parse a procedure / function
  *
  * @work: Input work
@@ -311,6 +341,11 @@ parse_token(struct np_work *work, struct lex_token *tok)
         /* XXX: NOP for testing */
         PIIR_PUSH(PIIR_NOP);
         break;
+    case TT_RETURN:
+        if ((error = parse_return(work, tok)) != 0) {
+            return -1;
+        }
+        break;
     }
 #undef PIIR_PUSH
     return 0;