From a342f45f820e28638e4a73a7b3a577ebf2396b0d Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Thu, 4 Apr 2019 18:48:42 +0200
Subject: Factor back in some rule branches

---
 dhall_core/src/parser.rs               | 93 ++++++++++++++++++----------------
 dhall_parser/src/dhall.abnf            | 64 +++++++++++------------
 dhall_parser/src/dhall.pest.visibility | 22 +++-----
 3 files changed, 84 insertions(+), 95 deletions(-)

diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index 68796c4..f888f94 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -116,8 +116,10 @@ fn debug_pair(pair: Pair<Rule>) -> String {
 
 macro_rules! make_parser {
     (@pattern, rule, $name:ident) => (Rule::$name);
+    (@pattern, token_rule, $name:ident) => (Rule::$name);
     (@pattern, rule_group, $name:ident) => (_);
     (@filter, rule) => (true);
+    (@filter, token_rule) => (true);
     (@filter, rule_group) => (false);
 
     (@body,
@@ -164,6 +166,13 @@ macro_rules! make_parser {
         ).ok_or_else(|| -> String { unreachable!() })?;
         Ok(ParsedValue::$group(res))
     });
+    (@body,
+        $pair:expr,
+        $children:expr,
+        token_rule!($name:ident<$o:ty>)
+    ) => ({
+        Ok(ParsedValue::$name(()))
+    });
     (@body, $pair:expr, $children:expr, rule_group!( $name:ident<$o:ty> )) => (
         unreachable!()
     );
@@ -235,7 +244,8 @@ fn do_parse<'a>(initial_pair: Pair<'a, Rule>) -> ParseResult<ParsedValue<'a>> {
 fn can_be_shortcutted(rule: Rule) -> bool {
     use Rule::*;
     match rule {
-        import_alt_expression
+        expression
+        | import_alt_expression
         | or_expression
         | plus_expression
         | text_append_expression
@@ -255,7 +265,7 @@ fn can_be_shortcutted(rule: Rule) -> bool {
 }
 
 make_parser! {
-    rule!(EOI<()>; captured_str!(_) => ());
+    token_rule!(EOI<()>);
 
     rule!(simple_label<Label>;
         captured_str!(s) => Label::from(s.trim().to_owned())
@@ -321,7 +331,7 @@ make_parser! {
         captured_str!(s) => s
     );
 
-    rule!(end_of_line<()>; captured_str!(_) => ());
+    token_rule!(end_of_line<()>);
 
     rule!(single_quote_literal<ParsedText>; children!(
         [end_of_line(eol), single_quote_continue(lines)] => {
@@ -392,9 +402,9 @@ make_parser! {
         },
     ));
 
-    rule!(NaN<()>; captured_str!(_) => ());
-    rule!(minus_infinity_literal<()>; captured_str!(_) => ());
-    rule!(plus_infinity_literal<()>; captured_str!(_) => ());
+    token_rule!(NaN<()>);
+    token_rule!(minus_infinity_literal<()>);
+    token_rule!(plus_infinity_literal<()>);
 
     rule!(double_literal<core::Double>;
         captured_str!(s) => {
@@ -491,7 +501,7 @@ make_parser! {
     rule!(bash_environment_variable<String>; captured_str!(s) => s.to_owned());
     rule!(posix_environment_variable<String>; captured_str!(s) => s.to_owned());
 
-    rule!(missing<()>; captured_str!(_) => ());
+    token_rule!(missing<()>);
 
     rule!(import_type<ImportLocation>; children!(
         [missing(_)] => {
@@ -522,9 +532,7 @@ make_parser! {
             ImportHashed { location, hash: Some(h) },
     ));
 
-    rule_group!(expression<ParsedExpr>);
-
-    rule!(Text<()>; captured_str!(_) => ());
+    token_rule!(Text<()>);
 
     rule!(import<ParsedExpr> as expression; children!(
         [import_hashed(location_hashed)] => {
@@ -541,25 +549,39 @@ make_parser! {
         },
     ));
 
-    rule!(lambda_expression<ParsedExpr> as expression; children!(
-        [nonreserved_label(l), expression(typ), expression(body)] => {
-            Expr::Lam(l, rc(typ), rc(body))
-        }
-    ));
+    token_rule!(lambda<()>);
+    token_rule!(forall<()>);
+    token_rule!(arrow<()>);
+    token_rule!(merge<()>);
+    token_rule!(if_<()>);
+    token_rule!(in_<()>);
 
-    rule!(ifthenelse_expression<ParsedExpr> as expression; children!(
-        [expression(cond), expression(left), expression(right)] => {
+    rule!(expression<ParsedExpr> as expression; children!(
+        [lambda(()), nonreserved_label(l), expression(typ), arrow(()), expression(body)] => {
+            Expr::Lam(l, rc(typ), rc(body))
+        },
+        [if_(()), expression(cond), expression(left), expression(right)] => {
             Expr::BoolIf(rc(cond), rc(left), rc(right))
-        }
-    ));
-
-    rule!(let_expression<ParsedExpr> as expression; children!(
-        [let_binding(bindings).., expression(final_expr)] => {
+        },
+        [let_binding(bindings).., in_(()), expression(final_expr)] => {
             bindings.fold(
                 final_expr,
                 |acc, x| Expr::Let(x.0, x.1, x.2, rc(acc))
             )
-        }
+        },
+        [forall(()), nonreserved_label(l), expression(typ), arrow(()), expression(body)] => {
+            Expr::Pi(l, rc(typ), rc(body))
+        },
+        [expression(typ), arrow(()), expression(body)] => {
+            Expr::Pi("_".into(), rc(typ), rc(body))
+        },
+        [merge(()), expression(x), expression(y), expression(z)] => {
+            Expr::Merge(rc(x), rc(y), Some(rc(z)))
+        },
+        [merge(()), expression(x), expression(y)] => {
+            Expr::Merge(rc(x), rc(y), None)
+        },
+        [expression(e)] => e,
     ));
 
     rule!(let_binding<(Label, Option<ParsedSubExpr>, ParsedSubExpr)>; children!(
@@ -569,27 +591,8 @@ make_parser! {
             (name, None, rc(expr)),
     ));
 
-    rule!(forall_expression<ParsedExpr> as expression; children!(
-        [nonreserved_label(l), expression(typ), expression(body)] => {
-            Expr::Pi(l, rc(typ), rc(body))
-        }
-    ));
-
-    rule!(arrow_expression<ParsedExpr> as expression; children!(
-        [expression(typ), expression(body)] => {
-            Expr::Pi("_".into(), rc(typ), rc(body))
-        }
-    ));
-
-    rule!(merge_expression<ParsedExpr> as expression; children!(
-        [expression(x), expression(y), expression(z)] =>
-            Expr::Merge(rc(x), rc(y), Some(rc(z))),
-        [expression(x), expression(y)] =>
-            Expr::Merge(rc(x), rc(y), None),
-    ));
-
-    rule!(List<()>; captured_str!(_) => ());
-    rule!(Optional<()>; captured_str!(_) => ());
+    token_rule!(List<()>);
+    token_rule!(Optional<()>);
 
     rule!(empty_collection<ParsedExpr> as expression; children!(
         [List(_), expression(t)] => {
@@ -830,7 +833,7 @@ make_parser! {
         },
     ));
 
-    rule!(empty_union_type<()>; captured_str!(_) => ());
+    token_rule!(empty_union_type<()>);
 
     rule!(non_empty_union_type_or_literal
           <(Option<(Label, ParsedSubExpr)>, BTreeMap<Label, ParsedSubExpr>)>;
diff --git a/dhall_parser/src/dhall.abnf b/dhall_parser/src/dhall.abnf
index 8964f44..2fad4d4 100644
--- a/dhall_parser/src/dhall.abnf
+++ b/dhall_parser/src/dhall.abnf
@@ -529,52 +529,46 @@ import = import-hashed [ whsp as whsp1 Text ]
 ; This is important to avoid the need for sequential backtracking in application-expression.
 
 expression =
-    lambda-expression
-    / ifthenelse-expression
-    / let-expression
-    / forall-expression
+    ; "\(x : a) -> b"
+      lambda whsp "(" whsp nonreserved-label whsp ":" whsp1 expression whsp ")" whsp arrow whsp expression
+    
+    ; "if a then b else c"
+    / if whsp1 expression whsp then whsp1 expression whsp else whsp1 expression
+    
+    ; "let x : t = e1 in e2"
+    ; "let x     = e1 in e2"
+    ; "let x = e1 let y = e2 in e3"
+    / 1*let-binding in whsp1 expression
+    
+    ; "forall (x : a) -> b"
+    / forall whsp "(" whsp nonreserved-label whsp ":" whsp1 expression whsp ")" whsp arrow whsp expression
+    
+    ; "a -> b"
     ; NOTE: Backtrack if parsing this alternative fails
-    / arrow-expression
-    / merge-expression
+    / operator-expression whsp arrow whsp expression
+    
+    ; "merge e1 e2 : t"
+    ; "merge e1 e2"
+    / merge whsp1 import-expression whsp import-expression [ whsp ":" whsp1 application-expression ]
+    
+    ; "[]  : List     t"
+    ; "[]  : Optional t"
+    ; "[x] : Optional t"
     ; NOTE: Backtrack if parsing this alternative fails since we can't tell
     ; from the opening bracket whether or not this will be an empty list or
     ; a non-empty list
-    / empty-list-or-optional
+    / "[" whsp (empty-collection / non-empty-optional)
+    
+    ; "x : t"
     / annotated-expression
 
-; "\(x : a) -> b"
-lambda-expression = lambda whsp "(" whsp nonreserved-label whsp ":" whsp1 expression whsp ")" whsp arrow whsp expression
-
-; "if a then b else c"
-ifthenelse-expression = if whsp1 expression whsp then whsp1 expression whsp else whsp1 expression
+; "x : t"
+annotated-expression = operator-expression [ whsp ":" whsp1 expression ]
 
-; "let x : t = e1 in e2"
-; "let x     = e1 in e2"
-; "let x = e1 let y = e2 in e3"
-let-expression = 1*let-binding in whsp1 expression
 let-binding = let whsp1 nonreserved-label whsp [ ":" whsp1 expression whsp ] "=" whsp expression whsp
-
-; "forall (x : a) -> b"
-forall-expression = forall whsp "(" whsp nonreserved-label whsp ":" whsp1 expression whsp ")" whsp arrow whsp expression
-
-; "a -> b"
-arrow-expression = operator-expression whsp arrow whsp expression
-
-; "merge e1 e2 : t"
-; "merge e1 e2"
-merge-expression = merge whsp1 import-expression whsp import-expression [ whsp ":" whsp1 application-expression ]
-
-; "[]  : List     t"
-; "[]  : Optional t"
-; "[x] : Optional t"
-empty-list-or-optional = "[" whsp (empty-collection / non-empty-optional)
 empty-collection = "]" whsp ":" whsp1 (List / Optional) whsp import-expression
 non-empty-optional = expression whsp "]" whsp ":" whsp1 Optional whsp import-expression
 
-; "x : t"
-annotated-expression = operator-expression [ whsp ":" whsp1 expression ]
-
-
 operator-expression = import-alt-expression
 
 ; Nonempty-whitespace to disambiguate `http://a/a?a`
diff --git a/dhall_parser/src/dhall.pest.visibility b/dhall_parser/src/dhall.pest.visibility
index e95cd32..ac3ea30 100644
--- a/dhall_parser/src/dhall.pest.visibility
+++ b/dhall_parser/src/dhall.pest.visibility
@@ -34,16 +34,15 @@ single_quote_literal
 # in
 # as
 # using
-# merge
 missing
-# if_
+if_
 # then
 # else_
 # let_
-# in_
+in_
 # as_
 # using
-# merge
+merge
 # Infinity
 Optional
 Text
@@ -78,9 +77,9 @@ List
 # combine
 # combine_types
 # prefer
-# lambda
-# forall
-# arrow
+lambda
+forall
+arrow
 # exponent
 double_literal
 natural_literal
@@ -120,14 +119,7 @@ import_type
 hash
 import_hashed
 import
-# expression
-lambda_expression
-ifthenelse_expression
-let_expression
-forall_expression
-arrow_expression
-merge_expression
-# empty_list_or_optional
+expression
 empty_collection
 non_empty_optional
 annotated_expression
-- 
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