diff --git a/README.md b/README.md index fbc4ec9..e5572db 100644 --- a/README.md +++ b/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 diff --git a/crsn/crsn-sexp/src/error.rs b/crsn/crsn-sexp/src/error.rs index e935717..cb5dea9 100644 --- a/crsn/crsn-sexp/src/error.rs +++ b/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. /// diff --git a/crsn/crsn-sexp/src/lib.rs b/crsn/crsn-sexp/src/lib.rs index 9eaf113..50815ab 100644 --- a/crsn/crsn-sexp/src/lib.rs +++ b/crsn/crsn-sexp/src/lib.rs @@ -331,10 +331,11 @@ fn parse_sexp(s: &str, pos: &mut usize) -> ERes { //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 diff --git a/crsn/src/asm/instr/cond.rs b/crsn/src/asm/instr/cond.rs index c3b86d3..5b72068 100644 --- a/crsn/src/asm/instr/cond.rs +++ b/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 { @@ -134,6 +138,7 @@ pub fn parse_cond(text: &str, pos: &SourcePosition) -> Result { "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, } } } diff --git a/crsn/src/asm/instr/flatten.rs b/crsn/src/asm/instr/flatten.rs index b307b7c..5af6a87 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()); + } + 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); } diff --git a/crsn/src/asm/instr/op.rs b/crsn/src/asm/instr/op.rs index 61fdf92..b81799f 100644 --- a/crsn/src/asm/instr/op.rs +++ b/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()); + } } } } diff --git a/crsn/src/runtime/frame/status.rs b/crsn/src/runtime/frame/status.rs index dec3d5a..286c897 100644 --- a/crsn/src/runtime/frame/status.rs +++ b/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, } } diff --git a/examples/test_cond.csn b/examples/test_cond.csn new file mode 100644 index 0000000..30877d8 --- /dev/null +++ b/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)) + ) +)