fix precedence parsing

Author: Geal

src/precedence/mod.rs

@@ -1,5 +1,5 @@
 //! Combinators to parse expressions with operator precedence.
-#![cfg(feature="alloc")]
+#![cfg(feature = "alloc")]
 #![cfg_attr(feature = "docsrs", doc(cfg(feature = "alloc")))]
 
 #[cfg(test)]
@@ -79,17 +79,11 @@ pub fn unary_op<I, O, E, P, Q>(
   mut parser: P,
 ) -> impl FnMut(I) -> IResult<I, Unary<O, Q>, E>
 where
-  P: Parser<I, O, E>,
+  P: Parser<I, Output = O, Error = E>,
   Q: Ord + Copy,
 {
   move |input| match parser.parse(input) {
-    Ok((i, value)) => Ok((
-      i,
-      Unary {
-        value,
-        precedence,
-      },
-    )),
+    Ok((i, value)) => Ok((i, Unary { value, precedence })),
     Err(e) => Err(e),
   }
 }
@@ -107,7 +101,7 @@ pub fn binary_op<I, O, E, P, Q>(
   mut parser: P,
 ) -> impl FnMut(I) -> IResult<I, Binary<O, Q>, E>
 where
-  P: Parser<I, O, E>,
+  P: Parser<I, Output = O, Error = E>,
   Q: Ord + Copy,
 {
   move |input| match parser.parse(input) {
@@ -124,7 +118,7 @@ where
 }
 
 /// Parses an expression with operator precedence.
-/// 
+///
 /// Supports prefix, postfix and binary operators. Operators are applied in ascending precedence.
 ///
 /// The parser will track its current position inside the expression and call the respective
@@ -146,7 +140,7 @@ where
 /// * `binary` Parser for binary operators.
 /// * `operand` Parser for operands.
 /// * `fold` Function that evaluates a single operation and returns the result.
-/// 
+///
 /// # Example
 /// ```rust
 /// # use nom::{Err, error::{Error, ErrorKind}, IResult};
@@ -156,11 +150,11 @@ where
 /// use nom::sequence::delimited;
 /// use nom::bytes::complete::tag;
 /// use nom::branch::alt;
-/// 
+///
 /// fn parser(i: &str) -> IResult<&str, i64> {
 ///   precedence(
 ///     unary_op(1, tag("-")),
-///     fail,
+///     fail(),
 ///     alt((
 ///       binary_op(2, Assoc::Left, tag("*")),
 ///       binary_op(2, Assoc::Left, tag("/")),
@@ -189,19 +183,19 @@ where
 /// assert_eq!(parser("4-(2+2)"), Ok(("", 0)));
 /// assert_eq!(parser("3-(2*3)+7+2*2-(2*(2+4))"), Ok(("", -4)));
 /// ```
-/// 
+///
 /// # Evaluation order
 /// This parser reads expressions from left to right and folds operations as soon as possible. This
 /// behaviour is only important when using an operator grammar that allows for ambigious expressions.
-/// 
+///
 /// For example, the expression `-a++**b` is ambigious with the following precedence.
-/// 
+///
 /// | Operator | Position | Precedence | Associativity |
 /// |----------|----------|------------|---------------|
 /// | **       | Binary   | 1          | Right         |
 /// | -        | Prefix   | 2          | N/A           |
 /// | ++       | Postfix  | 3          | N/A           |
-/// 
+///
 /// The expression can be parsed in two ways: `-((a++)**b)` or `((-a)++)**b`. This parser will always
 /// parse it as the latter because of how it evaluates expressions:
 /// * It reads, left-to-right, the first two operators `-a++`.
@@ -220,11 +214,11 @@ pub fn precedence<I, O, E, E2, F, G, H1, H3, H2, P1, P2, P3, Q>(
 where
   I: Clone + PartialEq,
   E: ParseError<I> + FromExternalError<I, E2>,
-  F: Parser<I, O, E>,
+  F: Parser<I, Output = O, Error = E>,
   G: FnMut(Operation<P1, P2, P3, O>) -> Result<O, E2>,
-  H1: Parser<I, Unary<P1, Q>, E>,
-  H2: Parser<I, Unary<P2, Q>, E>,
-  H3: Parser<I, Binary<P3, Q>, E>,
+  H1: Parser<I, Output = Unary<P1, Q>, Error = E>,
+  H2: Parser<I, Output = Unary<P2, Q>, Error = E>,
+  H3: Parser<I, Output = Binary<P3, Q>, Error = E>,
   Q: Ord + Copy,
 {
   move |mut i| {

src/precedence/tests.rs

@@ -3,10 +3,10 @@ use crate::{
   branch::alt,
   bytes::complete::tag,
   character::complete::digit1,
-  combinator::{map_res, fail},
+  combinator::{fail, map_res},
+  error::ErrorKind,
   internal::{Err, IResult},
   sequence::delimited,
-  error::ErrorKind,
 };
 
 #[cfg(feature = "alloc")]
@@ -16,7 +16,7 @@ use crate::precedence::precedence;
 fn parser(i: &str) -> IResult<&str, i64> {
   precedence(
     unary_op(1, tag("-")),
-    fail,
+    fail(),
     alt((
       binary_op(2, Assoc::Left, tag("*")),
       binary_op(2, Assoc::Left, tag("/")),
@@ -50,9 +50,9 @@ fn precedence_test() {
   assert_eq!(parser("4-2*2"), Ok(("", 0)));
   assert_eq!(parser("(4-2)*2"), Ok(("", 4)));
   assert_eq!(parser("2*2/1"), Ok(("", 4)));
-  
+
   let a = "a";
-  
+
   assert_eq!(
     parser(a),
     Err(Err::Error(error_node_position!(
@@ -61,9 +61,9 @@ fn precedence_test() {
       error_position!(&a[..], ErrorKind::Tag)
     )))
   );
-  
+
   let b = "3+b";
-  
+
   assert_eq!(
     parser(b),
     Err(Err::Error(error_node_position!(

tests/expression_ast.rs

@@ -1,12 +1,12 @@
 use nom::{
   branch::alt,
   bytes::complete::tag,
-  character::complete::{digit1 as digit, alphanumeric1 as alphanumeric},
-  combinator::{map_res, map},
+  character::complete::{alphanumeric1 as alphanumeric, digit1 as digit},
+  combinator::{map, map_res},
   multi::separated_list0,
+  precedence::{binary_op, precedence, unary_op, Assoc, Operation},
   sequence::delimited,
-  IResult,
-  precedence::{precedence, Assoc, binary_op, unary_op, Operation},
+  IResult, Parser,
 };
 
 // Elements of the abstract syntax tree (ast) that represents an expression.
@@ -29,25 +29,25 @@ pub enum Expr {
 
 // Prefix operators.
 enum PrefixOp {
-  Identity,           // +
-  Negate,             // -
+  Identity, // +
+  Negate,   // -
 }
 
 // Postfix operators.
 enum PostfixOp {
   // The function call operator. In addition to its own representation "()" it carries additional information that we need to keep here.
   // Specifically the vector of expressions that make up the parameters.
-  Call(Vec<Expr>),    // ()
+  Call(Vec<Expr>), // ()
 }
 
 // Binary operators.
 enum BinaryOp {
-  Addition,           // +
-  Subtraction,        // -
-  Multiplication,     // *
-  Division,           // /
+  Addition,       // +
+  Subtraction,    // -
+  Multiplication, // *
+  Division,       // /
   // The ternary operator can contain a single expression.
-  Ternary(Expr),      // ?:
+  Ternary(Expr), // ?:
 }
 
 // Parser for function calls.
@@ -57,31 +57,28 @@ fn function_call(i: &str) -> IResult<&str, PostfixOp> {
       tag("("),
       // Subexpressions are evaluated by recursing back into the expression parser.
       separated_list0(tag(","), expression),
-      tag(")")
+      tag(")"),
     ),
-    |v: Vec<Expr>| PostfixOp::Call(v)
-  )(i)
+    |v: Vec<Expr>| PostfixOp::Call(v),
+  )
+  .parse(i)
 }
 
 // The ternary operator is actually just a binary operator that contains another expression. So it can be
 // handled similarly to the function call operator except its in a binary position and can only contain
 // a single expression.
-// 
+//
 // For example the expression "a<b ? a : b" is handled similarly to the function call operator, the
 // "?" is treated like an opening bracket and the ":" is treated like a closing bracket.
 //
 // For the outer expression the result looks like "a<b ?: b". Where "?:" is a single operator. The
 // subexpression is contained within the operator in the same way that the function call operator
 // contains subexpressions.
 fn ternary_operator(i: &str) -> IResult<&str, BinaryOp> {
-  map(
-    delimited(
-      tag("?"), 
-      expression, 
-      tag(":")
-    ),
-    |e: Expr| BinaryOp::Ternary(e)
-  )(i)
+  map(delimited(tag("?"), expression, tag(":")), |e: Expr| {
+    BinaryOp::Ternary(e)
+  })
+  .parse(i)
 }
 
 // The actual expression parser .
@@ -94,65 +91,79 @@ fn expression(i: &str) -> IResult<&str, Expr> {
     // Function calls are implemented as postfix unary operators.
     unary_op(1, function_call),
     alt((
-      binary_op(3, Assoc::Left, alt((
-        map(tag("*"), |_| BinaryOp::Multiplication),
-        map(tag("/"), |_| BinaryOp::Division),
-      ))),
-      binary_op(4, Assoc::Left, alt((
-        map(tag("+"), |_| BinaryOp::Addition),
-        map(tag("-"), |_| BinaryOp::Subtraction),
-      ))),
+      binary_op(
+        3,
+        Assoc::Left,
+        alt((
+          map(tag("*"), |_| BinaryOp::Multiplication),
+          map(tag("/"), |_| BinaryOp::Division),
+        )),
+      ),
+      binary_op(
+        4,
+        Assoc::Left,
+        alt((
+          map(tag("+"), |_| BinaryOp::Addition),
+          map(tag("-"), |_| BinaryOp::Subtraction),
+        )),
+      ),
       // Ternary operators are just binary operators with a subexpression.
       binary_op(5, Assoc::Right, ternary_operator),
     )),
     alt((
-      map_res(digit,
-        |s: &str| match s.parse::<i64>() {
-          Ok(s) => Ok(Expr::Num(s)),
-          Err(e) => Err(e),
-        }
-      ),
+      map_res(digit, |s: &str| match s.parse::<i64>() {
+        Ok(s) => Ok(Expr::Num(s)),
+        Err(e) => Err(e),
+      }),
       map(alphanumeric, |s: &str| Expr::Iden(s.to_string())),
       delimited(tag("("), expression, tag(")")),
     )),
     |op: Operation<PrefixOp, PostfixOp, BinaryOp, Expr>| -> Result<Expr, ()> {
       use nom::precedence::Operation::*;
-      use PrefixOp::*;
-      use PostfixOp::*;
       use BinaryOp::*;
+      use PostfixOp::*;
+      use PrefixOp::*;
       match op {
         // The identity operator (prefix +) is ignored.
         Prefix(Identity, e) => Ok(e),
-        
+
         // Unary minus gets evaluated to the same representation as a multiplication with -1.
         Prefix(Negate, e) => Ok(Expr::Mul(Expr::Num(-1).into(), e.into())),
-        
+
         // The list of parameters are taken from the operator and placed into the ast.
         Postfix(e, Call(p)) => Ok(Expr::Call(e.into(), p)),
-        
+
         // Meaning is assigned to the expressions of the ternary operator during evaluation.
         // The lhs becomes the condition, the contained expression is the true case, rhs the false case.
         Binary(lhs, Ternary(e), rhs) => Ok(Expr::Tern(lhs.into(), e.into(), rhs.into())),
-        
+
         // Raw operators get turned into their respective ast nodes.
         Binary(lhs, Multiplication, rhs) => Ok(Expr::Mul(lhs.into(), rhs.into())),
         Binary(lhs, Division, rhs) => Ok(Expr::Div(lhs.into(), rhs.into())),
         Binary(lhs, Addition, rhs) => Ok(Expr::Add(lhs.into(), rhs.into())),
         Binary(lhs, Subtraction, rhs) => Ok(Expr::Sub(lhs.into(), rhs.into())),
       }
-    }
+    },
   )(i)
 }
 
 #[test]
 fn expression_test() {
   assert_eq!(
     expression("-2*max(2,3)-2").map(|(i, x)| (i, format!("{:?}", x))),
-    Ok(("", String::from("Sub(Mul(Mul(Num(-1), Num(2)), Call(Iden(\"max\"), [Num(2), Num(3)])), Num(2))")))
+    Ok((
+      "",
+      String::from("Sub(Mul(Mul(Num(-1), Num(2)), Call(Iden(\"max\"), [Num(2), Num(3)])), Num(2))")
+    ))
+  );
+
+  assert_eq!(
+    expression("a?2+c:-2*2").map(|(i, x)| (i, format!("{:?}", x))),
+    Ok((
+      "",
+      String::from(
+        "Tern(Iden(\"a\"), Add(Num(2), Iden(\"c\")), Mul(Mul(Num(-1), Num(2)), Num(2)))"
+      )
+    ))
   );
-  
- assert_eq!(
-   expression("a?2+c:-2*2").map(|(i, x)| (i, format!("{:?}", x))),
-   Ok(("", String::from("Tern(Iden(\"a\"), Add(Num(2), Iden(\"c\")), Mul(Mul(Num(-1), Num(2)), Num(2)))")))
- );
 }