add guard clauses to match and fn

src/main.rs

@@ -21,9 +21,9 @@
 //   - [x] with stack mechanics and refcounting
 //   - [ ] with tail-call optimization (nb: this may not be possible w/ a TW-VM)
 //   - [ ] with all the necessary forms for current Ludus
-//     * [ ] guards in match clauses
+//     * [x] guards in match clauses
 //     * [x] `as` patterns
-//     * [ ] splat patterns in tuples, lists, dicts
+//     * [x] splat patterns in tuples, lists, dicts
 //     * [ ] splats in list and dict literals
 //     * [ ] `loop` and `recur`
 //     * [ ] string patterns
@@ -55,28 +55,14 @@ use crate::base::*;
 
 pub fn main() {
     let src = "
-fn fancy_add {
-    () -> 0
-    (n as :number) -> n
-    (x as :number, y as :number) -> add (x, y)
-}
+fn t () -> true
+fn f () -> false
 
-fn fancy_sub {
-    () -> 0
-    (n as :number) -> n
-    (x as :number, y as :number) -> sub (x, y)
+fn id {
+    (x) if f () -> x
+    (x) -> :whoops
 }
-
-fn fib {
-   (1) -> 1
-   (2) -> 1
-   (n) -> fancy_add(
-       fib (fancy_sub (n, 1))
-       fib (fancy_sub (n, 2))
-   ) 
-}
-
-fib (30)
+id (:foo)
     ";
     let (tokens, lex_errs) = lexer().parse(src).into_output_errors();
     if lex_errs.len() > 0 {

src/parser.rs

@@ -211,12 +211,12 @@ pub enum Pattern<'src> {
     Keyword(&'src str),
     Word(&'src str),
     As(&'src str, &'src str),
+    Splattern(Box<Spanned<Self>>),
     Placeholder,
     Tuple(Vec<Spanned<Self>>),
     List(Vec<Spanned<Self>>),
-    // is this the right representation for Dicts?
-    // Could/should this also be a Vec?
-    Dict(Vec<Spanned<PairPattern<'src>>>),
+    Pair(&'src str, Box<Spanned<Self>>),
+    Dict(Vec<Spanned<Self>>),
 }
 
 impl<'src> fmt::Display for Pattern<'src> {
@@ -229,6 +229,7 @@ impl<'src> fmt::Display for Pattern<'src> {
             Pattern::Keyword(k) => write!(f, ":{}", k),
             Pattern::Word(w) => write!(f, "{}", w),
             Pattern::As(w, t) => write!(f, "{} as {}", w, t),
+            Pattern::Splattern(p) => write!(f, "...{}", (*p).0.to_string()),
             Pattern::Placeholder => write!(f, "_"),
             Pattern::Tuple(t) => write!(
                 f,
@@ -255,6 +256,7 @@ impl<'src> fmt::Display for Pattern<'src> {
                     .collect::<Vec<_>>()
                     .join(", ")
             ),
+            Pattern::Pair(key, value) => write!(f, ":{} {}", key, value.0),
         }
     }
 }
@@ -300,8 +302,24 @@ where
     }
     .map_with(|a, e| (a, e.span()));
 
+    let bare_splat = just(Token::Punctuation("...")).map_with(|_, e| {
+        (
+            Pattern::Splattern(Box::new((Pattern::Placeholder, e.span()))),
+            e.span(),
+        )
+    });
+
+    let splattable = word_pattern.clone().or(placeholder_pattern.clone());
+
+    let patt_splat = just(Token::Punctuation("..."))
+        .ignore_then(splattable)
+        .map_with(|x, e| (Pattern::Splattern(Box::new(x)), e.span()));
+
+    let splattern = patt_splat.or(bare_splat);
+
     let tuple_pattern = pattern
         .clone()
+        .or(splattern.clone())
         .separated_by(separators.clone())
         .allow_leading()
         .allow_trailing()
@@ -312,6 +330,7 @@ where
 
     let list_pattern = pattern
         .clone()
+        .or(splattern.clone())
         .separated_by(separators.clone())
         .allow_leading()
         .allow_trailing()
@@ -321,20 +340,18 @@ where
 
     let pair_pattern = select! {Token::Keyword(k) => k}
         .then(pattern.clone())
-        .map_with(|(key, patt), e| (PairPattern { key, patt }, e.span()));
+        .map_with(|(key, patt), e| (Pattern::Pair(key, Box::new(patt)), e.span()));
 
     let shorthand_pattern = select! {Token::Word(w) => w}.map_with(|w, e| {
         (
-            PairPattern {
-                key: w,
-                patt: ((Pattern::Word(w), e.span())),
-            },
+            Pattern::Pair(w, Box::new((Pattern::Word(w), e.span()))),
             e.span(),
         )
     });
 
     let dict_pattern = pair_pattern
         .or(shorthand_pattern)
+        .or(splattern.clone())
         .separated_by(separators.clone())
         .allow_leading()
         .allow_trailing()
@@ -504,6 +521,18 @@ where
         )
         .map_with(|clauses, e| (Ast::When(clauses), e.span()));
 
+    let guarded_clause = pattern
+        .clone()
+        .then_ignore(just(Token::Reserved("if")))
+        .then(simple.clone())
+        .then_ignore(just(Token::Punctuation("->")))
+        .then(expr.clone())
+        .map_with(|((patt, guard), body), _| MatchClause {
+            patt,
+            guard: Some(guard),
+            body,
+        });
+
     let match_clause = pattern
         .clone()
         .then_ignore(just(Token::Punctuation("->")))
@@ -520,6 +549,7 @@ where
         .then(
             match_clause
                 .clone()
+                .or(guarded_clause)
                 .separated_by(terminators.clone())
                 .allow_leading()
                 .allow_trailing()
@@ -556,6 +586,19 @@ where
         .then(block.clone())
         .map_with(|(count, body), e| (Ast::Repeat(Box::new(count), Box::new(body)), e.span()));
 
+    let fn_guarded = tuple_pattern
+        .clone()
+        .then_ignore(just(Token::Reserved("if")))
+        .then(simple.clone())
+        .then_ignore(just(Token::Punctuation("->")))
+        .then(nonbinding.clone())
+        .map_with(|((patt, guard), body), _| MatchClause {
+            patt,
+            body,
+            guard: Some(guard),
+        })
+        .labelled("function clause");
+
     let fn_clause = tuple_pattern
         .clone()
         .then_ignore(just(Token::Punctuation("->")))
@@ -626,7 +669,7 @@ where
 
     let fn_named = just(Token::Reserved("fn"))
         .ignore_then(word.clone())
-        .then(fn_clause.clone())
+        .then(fn_clause.clone().or(fn_guarded.clone()))
         .map_with(|(word, clause), e| {
             let name = if let Ast::Word(word) = word.0 {
                 word
@@ -641,6 +684,7 @@ where
         .then(
             fn_clause
                 .clone()
+                .or(fn_guarded.clone())
                 .separated_by(terminators.clone())
                 .allow_leading()
                 .allow_trailing()

src/vm.rs

@@ -79,51 +79,112 @@ pub fn match_pattern<'src, 'a>(
         }
         // todo: add splats to these match clauses
         (Pattern::Tuple(x), Value::Tuple(y)) => {
-            if x.len() != y.len() {
+            let has_splat = x.iter().any(|patt| {
+                if let (Pattern::Splattern(_), _) = patt {
+                    true
+                } else {
+                    false
+                }
+            });
+            if x.len() > y.len() || (!has_splat && x.len() != y.len()) {
                 return None;
             };
             let to = ctx.len();
             for i in 0..x.len() {
-                if let None = match_pattern(&x[i].0, &y[i], ctx) {
-                    while ctx.len() > to {
-                        ctx.pop();
+                if let Pattern::Splattern(patt) = &x[i].0 {
+                    let mut list = Vector::new();
+                    for i in i..y.len() {
+                        list.push_back(y[i].clone())
+                    }
+                    let list = Value::List(list);
+                    match_pattern(&(*patt).0, &list, ctx);
+                } else {
+                    if let None = match_pattern(&x[i].0, &y[i], ctx) {
+                        while ctx.len() > to {
+                            ctx.pop();
+                        }
+                        return None;
                     }
-                    return None;
                 }
             }
             Some(ctx)
         }
         (Pattern::List(x), Value::List(y)) => {
-            if x.len() != y.len() {
+            let has_splat = x.iter().any(|patt| {
+                if let (Pattern::Splattern(_), _) = patt {
+                    true
+                } else {
+                    false
+                }
+            });
+            if x.len() > y.len() || (!has_splat && x.len() != y.len()) {
                 return None;
             };
             let to = ctx.len();
             for i in 0..x.len() {
-                if let None = match_pattern(&x[i].0, y.get(i).unwrap(), ctx) {
-                    while ctx.len() > to {
-                        ctx.pop();
+                if let Pattern::Splattern(patt) = &x[i].0 {
+                    let list = Value::List(y.skip(i));
+                    match_pattern(&(*patt).0, &list, ctx);
+                } else {
+                    if let None = match_pattern(&x[i].0, &y.get(i).unwrap(), ctx) {
+                        while ctx.len() > to {
+                            ctx.pop();
+                        }
+                        return None;
                     }
-                    return None;
                 }
             }
             Some(ctx)
         }
+        // TODO: optimize this on several levels
+        // - [ ] opportunistic mutation
+        // - [ ] get rid of all the pointer indirection in word splats
         (Pattern::Dict(x), Value::Dict(y)) => {
-            if x.len() != y.len() {
+            let has_splat = x.iter().any(|patt| {
+                if let (Pattern::Splattern(_), _) = patt {
+                    true
+                } else {
+                    false
+                }
+            });
+            if x.len() > y.len() || (!has_splat && x.len() != y.len()) {
                 return None;
             };
             let to = ctx.len();
-            for (PairPattern { key, patt }, _) in x {
-                if let Some(val) = y.get(key) {
-                    if let None = match_pattern(&patt.0, val, ctx) {
-                        while ctx.len() > to {
-                            ctx.pop();
+            let mut matched = vec![];
+            for i in 0..x.len() {
+                let (pattern, _) = &x[i];
+                match pattern {
+                    Pattern::Pair(key, patt) => {
+                        if let Some(val) = y.get(key) {
+                            if let None = match_pattern(&patt.0, val, ctx) {
+                                while ctx.len() > to {
+                                    ctx.pop();
+                                    return None;
+                                }
+                            } else {
+                                matched.push(key);
+                            }
+                        } else {
                             return None;
-                        }
+                        };
                     }
-                } else {
-                    return None;
-                };
+                    Pattern::Splattern(pattern) => match &(*pattern).0 {
+                        Pattern::Word(w) => {
+                            // TODO: find a way to take ownership
+                            // this will ALWAYS make structural changes, because of this clone
+                            // we want opportunistic mutation if possible
+                            let mut unmatched = y.clone();
+                            for key in matched.iter() {
+                                unmatched.remove(*key);
+                            }
+                            ctx.push((*w, Value::Dict(unmatched)));
+                        }
+                        Pattern::Placeholder => (),
+                        _ => unreachable!(),
+                    },
+                    _ => unreachable!(),
+                }
             }
             Some(ctx)
         }
@@ -137,8 +198,24 @@ pub fn match_clauses<'src, 'a>(
     ctx: &'a mut Vec<(&'src str, Value<'src>)>,
 ) -> Result<Value<'src>, LudusError> {
     let to = ctx.len();
-    for MatchClause { patt, body, .. } in clauses.iter() {
+    for MatchClause { patt, body, guard } in clauses.iter() {
         if let Some(ctx) = match_pattern(&patt.0, value, ctx) {
+            let pass_guard = match guard {
+                None => true,
+                Some((ast, _)) => {
+                    let guard_res = eval(&ast, ctx);
+                    match &guard_res {
+                        Err(_) => return guard_res,
+                        Ok(val) => val.bool(),
+                    }
+                }
+            };
+            if !pass_guard {
+                while ctx.len() > to {
+                    ctx.pop();
+                }
+                continue;
+            }
             let res = eval(&body.0, ctx);
             while ctx.len() > to {
                 ctx.pop();
@@ -260,7 +337,9 @@ pub fn eval<'src, 'a>(
             let val = if let Some((_, value)) = ctx.iter().rev().find(|(name, _)| w == name) {
                 value.clone()
             } else {
-                unreachable!()
+                return Err(LudusError {
+                    msg: format!("unbound name {w}"),
+                });
             };
             Ok(val)
         }