Introduce chomp as a procedural macro.

Add a bunch of tests.

Fix chomp and chewed so autochomp compiles.

17 files changed, 427 insertions, 159 deletions

diff --git a/Cargo.toml b/Cargo.toml
index ca41e36..62fcc65 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,7 +5,7 @@ authors = ["Greg Brown <gmb60@cam.ac.uk>"]
 edition = "2018"
 
 [workspace]
-members = ["autochomp", "chewed"]
+members = ["autochomp", "chewed", "chomp-macro"]
 
 [dependencies]
 quote = "1"
diff --git a/autochomp/Cargo.toml b/autochomp/Cargo.toml
index 4e20c49..6dfd491 100644
--- a/autochomp/Cargo.toml
+++ b/autochomp/Cargo.toml
@@ -4,12 +4,10 @@ version = "0.1.0"
 authors = ["Greg Brown <gmb60@cam.ac.uk>"]
 edition = "2018"
 
-[build-dependencies]
-chomp = {path = ".."}
-
 [build-dependencies.syn]
 version = "1"
 features = ["extra-traits"]
 
 [dependencies]
 chewed = {path = "../chewed"}
+chomp-macro = {path = "../chomp-macro"}
diff --git a/autochomp/build.rs b/autochomp/build.rs
deleted file mode 100644
index 58c12a1..0000000
--- a/autochomp/build.rs
+++ /dev/null
@@ -1,78 +0,0 @@
-use std::{
-    env,
-    error::Error,
-    fmt::Display,
-    fs,
-    io::{Read, Write},
-    path::Path,
-    process::Command,
-};
-
-use chomp::{
-    chomp::{
-        check::{InlineCall, TypeCheck},
-        context::Context,
-        visit::Visitable,
-    },
-    lower::{rust::RustBackend, Backend, GenerateCode},
-    nibble::cst::File,
-};
-
-const PATH: &str = "src/nibble.nb";
-
-#[derive(Debug)]
-struct UndecVar;
-
-impl Display for UndecVar {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "Undeclared variable somewhere.")
-    }
-}
-impl Error for UndecVar {}
-
-fn main() {
-    println!("cargo:rerun-if-changed={}", PATH);
-
-    let out_dir = env::var("OUT_DIR").unwrap();
-
-    let mut input = String::new();
-
-    fs::File::open(PATH)
-        .map_err(|e| Box::new(e) as Box<dyn Error>)
-        .and_then(|mut file| {
-            file.read_to_string(&mut input)
-                .map_err(|e| Box::new(e) as Box<dyn Error>)
-        })
-        .and_then(|_| syn::parse_str(&input).map_err(|e| Box::new(e) as Box<dyn Error>))
-        .and_then(|nibble: File| nibble.convert().ok_or(Box::new(UndecVar) as Box<dyn Error>))
-        .and_then(|(funs, goal)| {
-            funs.into_iter()
-                .try_rfold(goal, |goal, function| {
-                    goal.fold(&mut InlineCall::new(function))
-                })
-                .map_err(|e| Box::new(e) as Box<dyn Error>)
-        })
-        .and_then(|term| {
-            let mut context = Context::default();
-            term.fold(&mut TypeCheck {
-                context: &mut context,
-            })
-            .map_err(|e| Box::new(e) as Box<dyn Error>)
-        })
-        .map(|typed| {
-            let mut backend = RustBackend::default();
-            let id = typed.gen(&mut backend);
-            backend.emit_code(id)
-        })
-        .and_then(|code| {
-            fs::File::create(Path::new(&out_dir).join("nibble.rs"))
-                .and_then(|mut f| write!(f, "{}", code))
-                .map_err(|e| Box::new(e) as Box<dyn Error>)
-        })
-        .unwrap();
-
-    Command::new("rustfmt")
-        .arg(&format!("{}/nibble.rs", out_dir))
-        .status()
-        .unwrap();
-}
diff --git a/autochomp/src/main.rs b/autochomp/src/main.rs
index 9b3b521..493204d 100644
--- a/autochomp/src/main.rs
+++ b/autochomp/src/main.rs
@@ -1,15 +1,12 @@
 use std::{
     error::Error,
-    fs,
     io::{self, Read, Write},
     process::exit,
 };
 
 use chewed::{IterWrapper, Parser};
 
-mod nibble {
-    include!(concat!(env!("OUT_DIR"), "/nibble.rs"));
-}
+mod nibble;
 
 fn main() {
     let mut input = String::new();
diff --git a/autochomp/src/nibble.nb b/autochomp/src/nibble.nb
deleted file mode 100644
index d454adf..0000000
--- a/autochomp/src/nibble.nb
+++ /dev/null
@@ -1,67 +0,0 @@
-let opt(x) = _ | x;
-let plus(x) = [plus](x . opt(plus));
-let star(x) = opt(plus(x));
-let star_(base, step) = [rec](base | step . rec);
-
-let Pattern_Whitespace = "\t"|"\n"|"\x0B"|"\x0c"|"\r"|" "|"\u{85}"|"\u{200e}"|"\u{200f}"|"\u{2028}"|"\u{2029}";
-
-let oct_digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" ;
-let digit     = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9";
-let hex_digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" |
-                "a" | "b" | "c" | "d" | "e" | "f" |
-                "A" | "B" | "C" | "D" | "E" | "F" ;
-
-let XID_Start =
-    "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" |
-    "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" |
-    "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" |
-    "y" | "z" |
-    "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" |
-    "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" |
-    "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" |
-    "Y" | "Z" ;
-let XID_Continue =
-    XID_Start | "_" | "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
-
-let literal_char =
-    " " | "!"       | "#" | "$" | "%" | "&" | "'" |
-    "(" | ")" | "*" | "+" | "," | "-" | "." | "/" |
-    "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
-    "8" | "9" | ":" | ";" | "<" | "=" | ">" | "?" |
-    "@" | "A" | "B" | "C" | "D" | "E" | "F" | "G" |
-    "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" |
-    "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" |
-    "X" | "Y" | "Z" | "["       | "]" | "^" | "_" |
-    "`" | "a" | "b" | "c" | "d" | "e" | "f" | "g" |
-    "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" |
-    "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" |
-    "x" | "y" | "z" | "{" | "|" | "}" | "~" |
-    "\\" . ("\"" | "'" | "n" | "r" | "t" | "\\" | "0" |
-            "x" . oct_digit . hex_digit |
-            "u{" . hex_digit . opt(hex_digit . opt(hex_digit . opt(hex_digit . opt(hex_digit . opt(hex_digit))))) . "}");
-
-let ws = plus(Pattern_Whitespace);
-
-let punctuated(x, p) = [rec](x . opt(p . opt(ws) . rec));
-let list(x) = "(" . opt(ws) . [rec](x . opt("," . opt(ws) . opt(rec))) . ")";
-
-let epsilon = "_";
-let ident = XID_Start . star(XID_Continue);
-let literal = "\"" . plus(literal_char) . "\"";
-let parens(expr) = "(" . opt(ws) . expr . ")";
-let fix(expr) = "[" . opt(ws) . ident . opt(ws) . "]" . opt(ws) . parens(expr);
-
-let term(expr) =
-      epsilon . opt(ws)
-    | literal . opt(ws)
-    | parens(expr) . opt(ws)
-    | fix(expr) . opt(ws)
-    | ident . opt(ws) . opt(list(expr) . opt(ws))
-    ;
-
-let seq(expr) = punctuated(term(expr), ".");
-let alt(expr) = punctuated(seq(expr), "|");
-let expr = [expr](alt(expr));
-let let = "let" . ws . ident . opt(ws) . opt(list(ident . opt(ws)) . opt(ws)) . "=" . opt(ws) . expr . ";";
-let goal = "match" . ws . expr . ";";
-match star_(goal, let);
diff --git a/autochomp/src/nibble.rs b/autochomp/src/nibble.rs
new file mode 100644
index 0000000..f6629f2
--- /dev/null
+++ b/autochomp/src/nibble.rs
@@ -0,0 +1,70 @@
+chomp_macro::nibble! {
+    let opt(x) = _ | x;
+    let plus(x) = [plus](x . opt(plus));
+    let star(x) = opt(plus(x));
+    let star_(base, step) = [rec](base | step . rec);
+
+    let Pattern_Whitespace = "\t"|"\n"|"\x0B"|"\x0c"|"\r"|" "|"\u{85}"|"\u{200e}"|"\u{200f}"|"\u{2028}"|"\u{2029}";
+
+    let oct_digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" ;
+    let digit     = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9";
+    let hex_digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" |
+                    "a" | "b" | "c" | "d" | "e" | "f" |
+                    "A" | "B" | "C" | "D" | "E" | "F" ;
+
+    let XID_Start =
+        "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" |
+        "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" |
+        "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" |
+        "y" | "z" |
+        "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" |
+        "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" |
+        "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" |
+        "Y" | "Z" ;
+    let XID_Continue =
+        XID_Start | "_" | "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
+
+    let literal_char =
+        " " | "!"       | "#" | "$" | "%" | "&" | "'" |
+        "(" | ")" | "*" | "+" | "," | "-" | "." | "/" |
+        "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
+        "8" | "9" | ":" | ";" | "<" | "=" | ">" | "?" |
+        "@" | "A" | "B" | "C" | "D" | "E" | "F" | "G" |
+        "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" |
+        "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" |
+        "X" | "Y" | "Z" | "["       | "]" | "^" | "_" |
+        "`" | "a" | "b" | "c" | "d" | "e" | "f" | "g" |
+        "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" |
+        "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" |
+        "x" | "y" | "z" | "{" | "|" | "}" | "~" |
+        "\\" . ("\"" | "'" | "n" | "r" | "t" | "\\" | "0" |
+                "x" . oct_digit . hex_digit |
+                "u{" . hex_digit . opt(hex_digit . opt(hex_digit . opt(hex_digit . opt(hex_digit . opt(hex_digit))))) . "}");
+
+    let ws = plus(Pattern_Whitespace);
+
+    let punctuated(x, p) = [rec](x . opt(p . opt(ws) . rec));
+    let list(x) = "(" . opt(ws) . [rec](x . opt("," . opt(ws) . opt(rec))) . ")";
+
+    let epsilon = "_";
+    let ident = XID_Start . star(XID_Continue);
+    let literal = "\"" . plus(literal_char) . "\"";
+    let parens(expr) = "(" . opt(ws) . expr . ")";
+    let fix(expr) = "[" . opt(ws) . ident . opt(ws) . "]" . opt(ws) . parens(expr);
+
+    let term(expr) =
+          epsilon . opt(ws)
+        | literal . opt(ws)
+        | parens(expr) . opt(ws)
+        | fix(expr) . opt(ws)
+        | ident . opt(ws) . opt(list(expr) . opt(ws))
+        ;
+
+    let cat(expr) = punctuated(term(expr), ".");
+    let alt(expr) = punctuated(cat(expr), "|");
+    let expr = [expr](alt(expr));
+    let let = "let" . ws . ident . opt(ws) . opt(list(ident . opt(ws)) . opt(ws)) . "=" . opt(ws) . expr . ";" . opt(ws);
+    let goal = "match" . ws . expr . ";" . opt(ws);
+
+    match star_(star_(goal, let), Pattern_Whitespace);
+}
diff --git a/chewed/src/parse.rs b/chewed/src/parse.rs
index 58bb94c..65e9272 100644
--- a/chewed/src/parse.rs
+++ b/chewed/src/parse.rs
@@ -21,7 +21,7 @@ pub trait Parser {
         P::parse(self)
     }
 
-    fn take_str(&mut self, s: &'static str) -> Result<(), TakeError> {
+    fn consume_str(&mut self, s: &'static str) -> Result<(), TakeError> {
         let mut count = 0;
 
         for exp in s.chars() {
@@ -114,6 +114,14 @@ pub trait Parse: Sized {
             Ok(res)
         }
     }
+
+    fn take_str(input: &str) -> Result<Self, TakeError> {
+        Self::take(&mut IterWrapper::new(input.chars()))
+    }
+
+    fn parse_str(input: &str) -> Result<Self, ParseError> {
+        Self::parse(IterWrapper::new(input.chars()))
+    }
 }
 
 impl Parse for () {
diff --git a/chomp-macro/Cargo.toml b/chomp-macro/Cargo.toml
new file mode 100644
index 0000000..bc8dce0
--- /dev/null
+++ b/chomp-macro/Cargo.toml
@@ -0,0 +1,18 @@
+[package]
+name = "chomp-macro"
+version = "0.1.0"
+authors = ["Greg Brown <gmb60@cam.ac.uk>"]
+edition = "2018"
+
+[dependencies]
+chomp = {path = ".."}
+
+[dependencies.syn]
+version = "1"
+features = ["parsing", "proc-macro"]
+
+[dev-dependencies]
+chewed = {path = "../chewed"}
+
+[lib]
+proc_macro = true
diff --git a/chomp-macro/src/lib.rs b/chomp-macro/src/lib.rs
new file mode 100644
index 0000000..d58bbdc
--- /dev/null
+++ b/chomp-macro/src/lib.rs
@@ -0,0 +1,42 @@
+use chomp::{
+    chomp::{
+        check::{InlineCalls, TypeCheck},
+        context::Context,
+        visit::Visitable,
+    },
+    lower::{rust::RustBackend, Backend, GenerateCode},
+    nibble::cst::File,
+};
+use proc_macro::{Span, TokenStream};
+use syn::Error;
+
+#[proc_macro]
+pub fn nibble(item: TokenStream) -> TokenStream {
+    syn::parse(item)
+        .and_then(|nibble: File| {
+            nibble
+                .convert()
+                .ok_or_else(|| todo!())
+        })
+        .and_then(|(funs, goal)| {
+            funs.into_iter()
+                .try_rfold(goal, |goal, function| {
+                    goal.fold(&mut InlineCalls::new(function))
+                })
+                .map_err(Error::from)
+        })
+        .and_then(|expr| {
+            let mut context = Context::default();
+            expr.fold(&mut TypeCheck {
+                context: &mut context,
+            })
+            .map_err(Error::from)
+        })
+        .map(|typed| {
+            let mut backend = RustBackend::default();
+            let id = typed.gen(&mut backend);
+            backend.emit_code(id)
+        })
+        .unwrap_or_else(Error::into_compile_error)
+        .into()
+}
diff --git a/chomp-macro/tests/nibble_exp.rs b/chomp-macro/tests/nibble_exp.rs
new file mode 100644
index 0000000..7e31e6a
--- /dev/null
+++ b/chomp-macro/tests/nibble_exp.rs
@@ -0,0 +1,81 @@
+chomp_macro::nibble! {
+    let opt(x) = _ | x;
+    let plus(x) = [plus](x . opt(plus));
+    let star(x) = [star](opt(x . star));
+
+    let Pattern_Whitespace = "\n"|" ";
+
+    let XID_Start =
+        "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" |
+        "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" |
+        "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" |
+        "y" | "z" |
+        "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" |
+        "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" |
+        "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" |
+        "Y" | "Z" ;
+    let XID_Continue =
+        XID_Start | "_" | "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
+
+    let literal_char = XID_Continue;
+
+    let ws = star(Pattern_Whitespace);
+    let must_ws = plus(Pattern_Whitespace);
+
+    let punctuated(x, p) = [rec](x . opt(p . ws . rec));
+    let list(x) = "(" . ws . [rec](x . opt("," . ws . opt(rec))) . ")";
+
+    let epsilon = "_";
+    let ident = XID_Start . star(XID_Continue);
+    let literal = "\"" . plus(literal_char) . "\"";
+    let parens(expr) = "(" . ws . expr . ")";
+    let fix(expr) = "[" . ws . ident . ws . "]" . ws . parens(expr);
+
+    let term(expr) =
+          epsilon . ws
+        | literal . ws
+        | parens(expr) . ws
+        | fix(expr) . ws
+        | ident . ws . opt(list(expr) . ws)
+        ;
+
+    let cat(expr) = punctuated(term(expr), ".");
+    let alt(expr) = punctuated(cat(expr), "|");
+    let expr = [expr](alt(expr));
+    match expr;
+}
+
+#[test]
+fn exp_epsilon() {
+    Ast::parse_str("_").unwrap();
+}
+
+#[test]
+fn exp_literal() {
+    Ast::parse_str(r#""foo""#).unwrap();
+}
+
+#[test]
+fn exp_cat() {
+    Ast::parse_str(r#""a" . "b""#).unwrap();
+}
+
+#[test]
+fn exp_alt() {
+    Ast::parse_str(r#""a" | "b""#).unwrap();
+}
+
+#[test]
+fn exp_ident() {
+    Ast::parse_str("foo").unwrap();
+}
+
+#[test]
+fn exp_call() {
+    Ast::parse_str(r#"opt("foo")"#).unwrap();
+}
+
+#[test]
+fn exp_fix() {
+    Ast::parse_str(r#"[rec](_ | "a" . rec)"#).unwrap();
+}
diff --git a/chomp-macro/tests/ratata.rs b/chomp-macro/tests/ratata.rs
new file mode 100644
index 0000000..869ad61
--- /dev/null
+++ b/chomp-macro/tests/ratata.rs
@@ -0,0 +1,15 @@
+chomp_macro::nibble! {
+    let opt(x) = _ | x;
+    let plus(x) = [rec](x . opt(rec));
+    match plus(("r" | "t") . "a");
+}
+
+#[test]
+fn ratata_ratata() {
+    Ast::parse_str("ratata").unwrap();
+}
+
+#[test]
+fn ratata_ratarataratatata() {
+    Ast::parse_str("ratarataratatata").unwrap();
+}
diff --git a/chomp-macro/tests/regex.rs b/chomp-macro/tests/regex.rs
new file mode 100644
index 0000000..1e831b4
--- /dev/null
+++ b/chomp-macro/tests/regex.rs
@@ -0,0 +1,27 @@
+chomp_macro::nibble! {
+    let opt(x) = _ | x;
+    let plus(x) = [plus](x . opt(plus));
+    let star(x) = [star](opt(x . star));
+
+    match plus("a") . star("b");
+}
+
+#[test]
+fn regex_a() {
+    Ast::parse_str("a").unwrap();
+}
+
+#[test]
+fn regex_ab() {
+    Ast::parse_str("ab").unwrap();
+}
+
+#[test]
+fn regex_aa() {
+    Ast::parse_str("aa").unwrap();
+}
+
+#[test]
+fn regex_aaaabbb() {
+    Ast::parse_str("aaaabbb").unwrap();
+}
diff --git a/chomp-macro/tests/regex_fix.rs b/chomp-macro/tests/regex_fix.rs
new file mode 100644
index 0000000..9842484
--- /dev/null
+++ b/chomp-macro/tests/regex_fix.rs
@@ -0,0 +1,11 @@
+chomp_macro::nibble! {
+    let opt(x) = _ | x;
+    let ws = [star](opt(" " . star));
+
+    match [rec]("a" . opt("." . ws . rec));
+}
+
+#[test]
+fn regex_fix_cat() {
+    Ast::parse_str(r#"a. a"#).unwrap();
+}
diff --git a/chomp-macro/tests/sheep.rs b/chomp-macro/tests/sheep.rs
new file mode 100644
index 0000000..862e810
--- /dev/null
+++ b/chomp-macro/tests/sheep.rs
@@ -0,0 +1,15 @@
+chomp_macro::nibble! {
+    let opt(x) = _ | x;
+    let plus(x) = [rec](x . opt(rec));
+    match "ba" . plus("a");
+}
+
+#[test]
+fn baa() {
+    Ast::parse_str("baa").unwrap();
+}
+
+#[test]
+fn baaaaaaaaaaaaaaa() {
+    Ast::parse_str("baaaaaaaaaaaaaaa").unwrap();
+}
diff --git a/src/chomp/check/inline.rs b/src/chomp/check/inline.rs
index 43a2eb8..da501f1 100644
--- a/src/chomp/check/inline.rs
+++ b/src/chomp/check/inline.rs
@@ -158,7 +158,7 @@ mod tests {
                 None,
             )
             .into(),
-            None
+            None,
         );
         let inlined = expr.fold(&mut InlineCalls::new(function));
         assert_eq!(
@@ -208,7 +208,7 @@ mod tests {
                 None,
             )
             .into(),
-            None
+            None,
         );
         let inlined = expr.fold(&mut InlineCalls::new(function));
         assert_eq!(
@@ -231,4 +231,119 @@ mod tests {
             .into())
         )
     }
+
+    #[test]
+    fn test_inline_double_subst() {
+        let expr = Call::new(
+            Name::Spanless("opt".to_string()),
+            vec![Call::new(
+                Name::Spanless("opt".to_string()),
+                vec![Literal::Spanless("x".to_string()).into()],
+                None,
+            )
+            .into()],
+            None,
+        );
+        let inlined = expr.fold(&mut InlineCalls::new(opt()));
+        assert_eq!(
+            inlined,
+            Ok(Alt::new(
+                Epsilon::default().into(),
+                None,
+                Alt::new(
+                    Epsilon::default().into(),
+                    None,
+                    Literal::Spanless("x".to_string()).into()
+                )
+                .into()
+            )
+            .into())
+        )
+    }
+
+    #[test]
+    fn test_inline_call_args() {
+        let expr = Fix::new(
+            Name::Spanless("rec".to_string()),
+            Cat::new(
+                Literal::Spanless("a".to_string()).into(),
+                None,
+                Call::new(
+                    Name::Spanless("opt".to_string()),
+                    vec![Cat::new(
+                        Cat::new(
+                            Literal::Spanless("a".to_string()).into(),
+                            None,
+                            Fix::new(
+                                Name::Spanless("star".to_string()),
+                                Call::new(
+                                    Name::Spanless("opt".to_string()),
+                                    vec![Cat::new(
+                                        Literal::Spanless(" ".to_string()).into(),
+                                        None,
+                                        Variable::new(Name::Spanless("star".to_string()), 0).into(),
+                                    )
+                                    .into()],
+                                    None,
+                                )
+                                .into(),
+                                None,
+                            )
+                            .into(),
+                        )
+                        .into(),
+                        None,
+                        Variable::new(Name::Spanless("rec".to_string()), 0).into(),
+                    )
+                    .into()],
+                    None,
+                )
+                .into(),
+            )
+            .into(),
+            None,
+        );
+        let inlined = expr.fold(&mut InlineCalls::new(opt()));
+        assert_eq!(inlined,
+        Ok(Fix::new(
+            Name::Spanless("rec".to_string()),
+            Cat::new(
+                Literal::Spanless("a".to_string()).into(),
+                None,
+                Alt::new(
+                    Epsilon::default().into(),
+                    None,
+                    Cat::new(
+                        Cat::new(
+                            Literal::Spanless("a".to_string()).into(),
+                            None,
+                            Fix::new(
+                                Name::Spanless("star".to_string()),
+                                Alt::new(
+                                    Epsilon::default().into(),
+                                    None,
+                                    Cat::new(
+                                        Literal::Spanless(" ".to_string()).into(),
+                                        None,
+                                        Variable::new(Name::Spanless("star".to_string()), 0).into(),
+                                    )
+                                        .into()
+                                )
+                                .into(),
+                                None,
+                            )
+                            .into(),
+                        )
+                        .into(),
+                        None,
+                        Variable::new(Name::Spanless("rec".to_string()), 0).into(),
+                    )
+                    .into(),
+                )
+                .into(),
+            )
+            .into(),
+            None,
+        ).into()))
+    }
 }
diff --git a/src/chomp/error.rs b/src/chomp/error.rs
index ffcbdd0..e7e4660 100644
--- a/src/chomp/error.rs
+++ b/src/chomp/error.rs
@@ -358,6 +358,19 @@ pub enum SubstituteError {
     WrongArgCount { call: Call, expected: usize },
 }
 
+impl From<SubstituteError> for syn::Error {
+    fn from(e: SubstituteError) -> Self {
+        match e {
+            SubstituteError::FreeParameter(param) => {
+                Self::new(param.name().span().unwrap_or_else(Span::call_site), format!("undeclared variable `{}'", param.name()))
+            }
+            SubstituteError::WrongArgCount { call, expected } => {
+                Self::new(call.span().unwrap_or_else(Span::call_site), format!("wrong number of arguments. Expected {}, got {}", expected, call.args().len()))
+            }
+        }
+    }
+}
+
 impl Display for SubstituteError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
@@ -378,8 +391,8 @@ impl Display for SubstituteError {
                     "{}:{}: wrong number of arguments. Expected {}, got {}",
                     start.line,
                     start.column,
-                    call.args().len(),
-                    expected
+                    expected,
+                    call.args().len()
                 )
             }
         }
diff --git a/src/lower/rust.rs b/src/lower/rust.rs
index 74deb73..7931306 100644
--- a/src/lower/rust.rs
+++ b/src/lower/rust.rs
@@ -75,7 +75,7 @@ impl Backend for RustBackend {
 
                 impl Parse for #name {
                     fn take<P: Parser + ?Sized>(input: &mut P) -> Result<Self, TakeError> {
-                        input.take_str(#lit).map(|()| #name)
+                        input.consume_str(#lit).map(|()| #name)
                     }
                 }
             };
@@ -206,8 +206,11 @@ impl Backend for RustBackend {
                 TokenStream::new(),
                 BTreeSet::new(),
             ));
+
             self.context.push(id);
             let inner = inner.gen(self);
+            self.context.pop();
+
             let inner_ty = self.data[inner].0.clone();
             let tokens = quote! {
                 #[derive(Clone, Debug, Eq, Hash, PartialEq)]