duskos

commit 8fb909c8bdd8783e55e9f37474fd8ca9bc26d677
parent 808d2da630e13ff60b4eee260d601eb50789844f
Author: Virgil Dupras <hsoft@hardcoded.net>
Date:   Sat, 18 Jun 2022 10:04:00 -0400

Add case..endcase

With a special twist! I'm happy about how it turns out. Will greatly help in
cc/vm code.

Diffstat:
M
fs/cc/ast.fs
 | 
23
++++++++++++-----------
M
fs/lib/core.fs
 | 
16
++++++++++++++++
M
fs/tests/core.fs
 | 
13
+++++++++++++

3 files changed, 41 insertions(+), 11 deletions(-)
diff --git a/fs/cc/ast.fs b/fs/cc/ast.fs
@@ -132,14 +132,14 @@ alias noop parseExpression ( tok -- node ) \ forward declaration
 \ 4. A function call
 \ 5. An expression inside () parens.
 : parseFactor ( tok -- node-or-0 )
-  dup S" (" s= if ( tok )
-    drop nextt parseExpression nextt ')' expectChar exit then
-  dup uopid if ( tok opid )
-    nip AST_UNARYOP createnode swap , ( opnode )
-    nextt parseFactor ?dup _assert over addnode ( opnode )
-    exit then ( tok )
-  dup isIdent? if \ lvalue or FunCall
-    nextt ( prevtok newtok ) dup S" (" s= if \ FunCall
+  case
+  S" (" of s= ( )
+    nextt parseExpression nextt ')' expectChar endof
+  of uopid ( opid )
+    AST_UNARYOP createnode swap , ( opnode )
+    nextt parseFactor ?dup _assert over addnode ( opnode ) endof
+  of isIdent? ( ) \ lvalue or FunCall
+    r@ nextt ( prevtok newtok ) dup S" (" s= if \ FunCall
       drop AST_FUNCALL createnode swap , begin ( node )
         nextt dup parseFactor ?dup if \ an argument
           nip over addnode
@@ -150,9 +150,10 @@ alias noop parseExpression ( tok -- node ) \ forward declaration
       swap AST_LVALUE createnode swap , ( tok lvnode )
       swap parsePostfixOp ( lvnode node-or-0 ) ?dup if ( lvnode opnode )
         tuck addnode then ( lv-or-op-node ) then
-  else \ Constant
-    parse if AST_CONSTANT createnode swap , else 0 then
-  then ;
+  endof
+  ( case else ) \ Constant
+    r@ parse if AST_CONSTANT createnode swap , else 0 then
+  endcase ;
 
 \ An expression can be 2 things:
 \ 1. a factor
diff --git a/fs/lib/core.fs b/fs/lib/core.fs
@@ -47,6 +47,22 @@ $08 const BS  $04 const EOF
 : wordname[] ( w -- sa sl )
   dup wordlen swap 5 - over - ( sl sa ) swap ;
 
+\ case..endcase
+\ The case statement is very similar to what we see in other forths, but with
+\ one major difference: the "of" word specifies the thruth word. So, the
+\ "of" we see in other forths is equivalent to "of =" in Dusk OS. The comparator
+\ has to be a single word following "of".
+\ case x of = ... endof y of < ... endof ... endcase
+\ is syntactic sugar for:
+\ >r x r@ = if ... else y r@ < if ... else ... then then r~
+\ NOTE: if you want to access your reference value in the final "else", you
+\ need to use "r@".
+: case ( -- then-stopgap ) 0 compile >r ; immediate
+: of ( -- jump-addr ) compile r@ ' call, [compile] if ; immediate
+alias else endof immediate
+: endcase ( then-stopgap jump1? jump2? ... jumpn? -- )
+  ?dup if begin [compile] then ?dup not until then compile r~ ; immediate
+
 \ Number formatting
 create _ ," 0123456789abcdef"
 : .xh $f and _ + c@ emit ;
diff --git a/fs/tests/core.fs b/fs/tests/core.fs
@@ -16,4 +16,17 @@ foo 43 #eq
 5 to+ foo
 foo 48 #eq
 to' foo @ 48 #eq
+
+\ case
+: foo ( n ) case
+    1 of = 111 endof
+    42 of > 222 endof
+    333
+  endcase ;
+
+1 foo 111 #eq
+2 foo 222 #eq
+3 foo 222 #eq
+42 foo 333 #eq
+
 testend