From 0006cd06ece8dee97e67e85dbf570dbe52dd2ec6 Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Thu, 22 Oct 2020 20:05:33 +0100
Subject: [PATCH] Reduce true/false conditionals down to just 'else' and warn
 if else is used in non-final branch

---
 crsn/src/asm/instr/cond.rs    |  7 +++----
 crsn/src/asm/instr/flatten.rs |  4 ++++
 examples/test_cond.csn        | 11 ++---------
 3 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/crsn/src/asm/instr/cond.rs b/crsn/src/asm/instr/cond.rs
index 13ff6c9..5b72068 100644
--- a/crsn/src/asm/instr/cond.rs
+++ b/crsn/src/asm/instr/cond.rs
@@ -138,8 +138,7 @@ pub fn parse_cond(text: &str, pos: &SourcePosition) -> Result<Cond, CrsnError> {
         "neof" => Cond::NotEof,
         "ov" => Cond::Overflow,
         "nov" => Cond::NotOverflow,
-        "true" | "always" | "else" => Cond::True,
-        "false" | "never" => Cond::False,
+        "else" => Cond::True,
         _ => {
             return Err(CrsnError::Parse(format!("Unknown cond: {}", text).into(), pos.clone()));
         }
@@ -180,8 +179,8 @@ impl Display for Cond {
             Cond::Valid => "valid",
             Cond::Eof => "eof",
             Cond::NotEof => "neof",
-            Cond::True => "true",
-            Cond::False => "false",
+            Cond::True => "else",
+            Cond::False => "never",
         })
     }
 }
diff --git a/crsn/src/asm/instr/flatten.rs b/crsn/src/asm/instr/flatten.rs
index b307b7c..d66721a 100644
--- a/crsn/src/asm/instr/flatten.rs
+++ b/crsn/src/asm/instr/flatten.rs
@@ -49,6 +49,10 @@ impl Flatten for InstrWithBranches {
                     return Err(CrsnError::Asm(AsmError::ConditionalAlreadyUsed(cond), branch.pos()));
                 }
 
+                if cnt != branch_count - 1 && cond == Cond::True {
+                    warn!("\"Else\" conditional used in non-final branch at {}:{}", branch.pos().line, branch.pos().column);
+                }
+
                 let next_lbl = if cnt == branch_count - 1 {
                     end_lbl.clone()
                 } else {
diff --git a/examples/test_cond.csn b/examples/test_cond.csn
index b4a5208..fc45bce 100644
--- a/examples/test_cond.csn
+++ b/examples/test_cond.csn
@@ -2,7 +2,7 @@
   (ld r8 0)
 
   (ld r0 1
-    (true? (add r8 1))
+    (else? (add r8 1))
   )
 
   (sub r0 1
@@ -10,15 +10,8 @@
     (else? (add r8 1))
   )
 
-  (nop
-    (always? (add r8 1))
-  )
-
-  (nop
-    (never? (fault))
-  )
 
-  (cmp r8 3
+  (cmp r8 2
     (ne? (fault))
   )
 )