Merge branch 'nat-master' into master

README.md

@@ -98,6 +98,7 @@ These keywords (among others) are used in conditional branches to specify flag t
 - `nem`, `nempty` … Not empty
 - `eof` … EOF
 - `neof` … Not EOF
+- `else` … Always true, may be used in the last branch
 
 # Syntax
 
@@ -207,6 +208,7 @@ Conditonal branches are written like this:
   then only one branch is taken - there is no fall-through.
 - The definition order is preserved, i.e. if the `inval` flag is to be checked, it should be done 
   before checking e.g. `nz`, which is, incidentally, true by default, because most flags are cleared by instructions that affects flags.
+- `else` can be used as a final choice of branch that will always be taken.
 
 ## Routines
 

crsn/crsn-sexp/src/error.rs

@@ -19,6 +19,12 @@ pub struct SourcePosition {
     pub index: u32,
 }
 
+impl fmt::Display for SourcePosition {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        write!(f, "{}:{}", self.line, self.column)
+    }
+}
+
 /// Since errors are the uncommon case, they're boxed. This keeps the size of
 /// structs down, which helps performance in the common case.
 ///

crsn/crsn-sexp/src/lib.rs

@@ -331,10 +331,11 @@ fn parse_sexp(s: &str, pos: &mut usize) -> ERes<Sexp> {
     //trace!("parse_sexp {}", pos);
     zspace(s, pos)?;
     let (c, _) = peek(s, *pos)?;
+    let pos0 = *pos;
     let r = if c == '(' {
-        Ok(Sexp::List(parse_list(s, pos)?, spos(s, *pos)))
+        Ok(Sexp::List(parse_list(s, pos)?, spos(s, pos0)))
     } else {
-        Ok(Sexp::Atom(parse_atom(s, pos)?, spos(s, *pos)))
+        Ok(Sexp::Atom(parse_atom(s, pos)?, spos(s, pos0)))
     };
     zspace(s, pos)?;
     r

crsn/src/asm/instr/cond.rs

@@ -106,6 +106,10 @@ pub enum Cond {
     Eof,
     /// Not empty
     NotEof,
+    // Always true, for eg. (else? ...)
+    True,
+    /// Always false
+    False,
 }
 
 pub fn parse_cond(text: &str, pos: &SourcePosition) -> Result<Cond, CrsnError> {
@@ -134,6 +138,7 @@ pub fn parse_cond(text: &str, pos: &SourcePosition) -> Result<Cond, CrsnError> {
         "neof" => Cond::NotEof,
         "ov" => Cond::Overflow,
         "nov" => Cond::NotOverflow,
+        "else" => Cond::True,
         _ => {
             return Err(CrsnError::Parse(format!("Unknown cond: {}", text).into(), pos.clone()));
         }
@@ -174,6 +179,8 @@ impl Display for Cond {
             Cond::Valid => "valid",
             Cond::Eof => "eof",
             Cond::NotEof => "neof",
+            Cond::True => "else",
+            Cond::False => "never",
         })
     }
 }
@@ -214,6 +221,9 @@ impl Not for Cond {
 
             Cond::NotEof => Cond::Eof,
             Cond::Eof => Cond::NotEof,
+
+            Cond::True => Cond::False,
+            Cond::False => Cond::True,
         }
     }
 }

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());
+                }
+
                 let next_lbl = if cnt == branch_count - 1 {
                     end_lbl.clone()
                 } else {
@@ -64,11 +68,13 @@ impl Flatten for InstrWithBranches {
                     // optimization for single-branch conditionals with a single instruction
                     ops.push(Op { cond: Some(cond), pos: pos.clone(), kind: flattened.remove(0).kind });
                 } else {
-                    ops.push(Op {
-                        kind: OpKind::BuiltIn(BuiltinOp::Jump(next_lbl.clone())),
-                        pos: pos.clone(),
-                        cond: Some(!cond),
-                    });
+                    if cond != Cond::True { // evoid emiting `op.never`
+                        ops.push(Op {
+                            kind: OpKind::BuiltIn(BuiltinOp::Jump(next_lbl.clone())),
+                            pos: pos.clone(),
+                            cond: Some(!cond),
+                        });
+                    }
                     ops.extend(flattened);
                 }
 

crsn/src/asm/instr/op.rs

@@ -50,11 +50,15 @@ impl OpTrait for Op {
             OpKind::Ext(op) => op.to_sexp()
         };
 
+        // TODO rewrite to be more readable?
         if let Some(cond) = self.cond {
-            if let Sexp::List(items, _) = &mut se {
-                if let Some(Sexp::Atom(Atom::S(s), _)) = &mut items.get_mut(0) {
-                    s.push('.');
-                    s.push_str(&cond.to_string());
+            // "true" is used for "else" branches, it has no effect - just omit it
+            if cond != Cond::True {
+                if let Sexp::List(items, _) = &mut se {
+                    if let Some(Sexp::Atom(Atom::S(s), _)) = &mut items.get_mut(0) {
+                        s.push('.');
+                        s.push_str(&cond.to_string());
+                    }
                 }
             }
         }

crsn/src/runtime/frame/status.rs

@@ -115,6 +115,8 @@ impl StatusFlags {
             Cond::NotEmpty => !self.empty,
             Cond::Eof => self.eof,
             Cond::NotEof => !self.eof,
+            Cond::True => true,
+            Cond::False => false,
         }
     }
 

examples/test_cond.csn

@@ -0,0 +1,36 @@
+(
+  ; test else
+
+  (cmp 0 5
+    (eq? (fault))
+    (else? (ld r0 15))
+    (lt? (fault)) ; This should produce a warning
+  )
+  (cmp 15 r0
+    (ne? (fault "else did not run")))
+
+  (ld r0 0)
+
+  (cmp 0 5
+    (lt? (nop))
+    (else? (fault "fallthrough to else"))
+  )
+
+  ;
+
+  (ld r8 0)
+
+  (ld r0 1
+    (else? (add r8 1))
+  )
+
+  (sub r0 1
+    (pos? (fault))
+    (else? (add r8 1))
+  )
+
+
+  (cmp r8 2
+    (ne? (fault))
+  )
+)