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-Subproject commit 513173b22fa4776c54cae4bb6b78dcc8ec9acac9
diff --git a/uann.tar.gz b/uann.tar.gz
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diff --git a/uann/Cargo.lock b/uann/Cargo.lock
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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "parsing"
+version = "0.1.0"
+dependencies = [
+ "unicode-segmentation",
+]
+
+[[package]]
+name = "unicode-segmentation"
+version = "1.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1dd624098567895118886609431a7c3b8f516e41d30e0643f03d94592a147e36"
diff --git a/uann/Cargo.toml b/uann/Cargo.toml
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+[package]
+name = "parsing"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+unicode-segmentation = "1.6.0"
\ No newline at end of file
diff --git a/uann/README.md b/uann/README.md
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+# uann
+A compiler practice or a parser's practice
diff --git a/uann/src/main.rs b/uann/src/main.rs
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+/// (c) 2023 Tan Kian-ting <yoxem@kianting.info> 
+/// Under MIT License
+/// 习包子 梁家河小学博士 清零宗 习炀帝 庆丰大帝
+/// 独裁国贼 新疆集中营 光复香港时代革命 祈翠 南蒙古独立 香港独立
+/// 
+
+///
+/// pairs of string for matching and parsing
+/// 
+/// - `matched` : the string being accumulatedly matched.
+/// - `remained` : the string to be matched
+#[derive(Debug, Clone, PartialEq)]
+pub struct Matchee {
+    matched : String,
+    remained : String,
+}
+
+/// macro convert a str as a string, equivalent to `x.to_string()`.
+/// 
+/// # Example:
+/// ```
+/// let a = "abc";
+/// assert_eq!(string!(a), a.to_string());
+/// ```
+///
+macro_rules! string {
+    ($name:expr) => {$name.to_string()}
+}
+
+
+/// then!(a, b [, c...]*) i similar to
+/// a ==> b ((==> c)...)*
+macro_rules! then{
+
+    ($item: expr, $closure1: expr, $($closure2: expr),+)=>{
+        then!(then_do($item, &$closure1), $($closure2),+);
+    };
+    ($item: expr, $closure1: expr)=>{
+        then_do($item, &$closure1);
+    };
+}
+
+
+/// convert a string to 
+/// a vector of char
+/// 
+///  * s : input `str`'s reference
+/// 
+/// # Example
+/// 
+/// ```
+/// let s = "Lí 好！";
+/// let char_vec: Vec<char> = str_to_char_vec(s);
+/// assert_eq!(char_vec, vec!['L','í',' ','好','！'])
+/// ```
+fn str_to_char_vec (s : &str) -> Vec<char>{
+    return s.chars().collect();
+}
+
+/// return a closure such that
+/// if the 1st char of `Matchee.matched` matches `ch`,
+/// then return the new `Some<Matchee>`. Otherwise, it returns `None`.
+fn match_1_char(ch : char) -> Box<dyn Fn(Matchee) -> Option<Matchee>>{
+    return match_range(ch, ch)
+}
+
+/// return a closure such that
+/// if the codepoint of the 1st char of `Matchee.matched` between
+/// that of `lower_ch` (lower bound) and that of `upper_ch` (upper bound)
+/// then return the new updated `Some<Matchee>`.
+/// Otherwise, it returns `None`.
+/// 
+fn match_range(lower_ch : char, upper_ch: char) ->
+    Box<dyn Fn(Matchee) -> Option<Matchee>> {
+    Box::new(move | x : Matchee| -> Option<Matchee> {
+        let x_remained_str = x.remained.as_str();
+        let x_remained_char_vec = str_to_char_vec(x_remained_str);
+
+        if x_remained_char_vec.len() == 0{
+            return None;
+        }
+
+        if (x_remained_char_vec[0] as u32) >= (lower_ch as u32) && 
+        (x_remained_char_vec[0] as u32) <= (upper_ch as u32){
+            let remained_string = x_remained_char_vec[1..].iter()
+                                    .collect::<String>();
+            return Some(Matchee{
+                matched : x.matched + &x_remained_char_vec[0].to_string(),
+                remained : remained_string,
+            });
+        }else{
+            return None;
+        }
+    })
+}
+
+///
+/// like the infix `==>` monad, i.e. `inputee ==> closure` in OCaml,
+/// return a combinable closure.
+/// - `inputee` : input string wrapped by Some() or None
+/// - `closure` : the input to be processed
+fn then_do(inputee : Option<Matchee>, closure : &dyn Fn(Matchee) -> Option<Matchee>)
+    -> Option<Matchee>{
+        return match inputee {
+            Some(inner) => closure(inner),
+            None => inputee,
+        }
+    }
+/// return a closure for what is do 0+ times
+/// similar to `( closure )*`
+fn zero_plus_times_do(closure : &dyn Fn(Matchee) -> Option<Matchee>) ->
+Box<dyn Fn(Matchee) -> Option<Matchee> + '_>{
+    return Box::new(
+        move |inputee|{
+            let mut old_inputee = inputee.clone();
+            let mut new_inputee = closure(old_inputee.clone());
+        while let Some(new_inner) = new_inputee
+        {
+            old_inputee = new_inner.clone();
+            new_inputee = closure(new_inner);
+        }
+        return Some(old_inputee.clone());
+    });
+}
+
+/// return a combined closure. if `closure1` is not passed, then 
+/// use `closure2`, i.e. : `(closure1 || closure2)`
+fn or_do(
+    closure1 : Box<dyn Fn(Matchee) -> Option<Matchee>>,
+    closure2 : Box<dyn Fn(Matchee) -> Option<Matchee>>) -> 
+    Box<dyn Fn(Matchee) -> Option<Matchee>>{
+        Box::new(
+            move |inputee|{
+                let inputee_after_c1 = closure1(inputee.clone());
+                match inputee_after_c1 {
+                    None => closure2(inputee.clone()),
+                    _ => inputee_after_c1,
+                }
+            }
+        )    
+    }
+
+
+fn main() {
+    let ex1 = Matchee{
+                matched : string!(""),
+                remained : string!("112")};
+
+    let d = match_range('0', '9');
+    println!("{:?}", then_do(then_do(then_do(Some(ex1.clone()), &d), &d), &d));
+
+    println!("{:?}", (ex1.clone()));
+    println!("{:?}", match_range('2', '9')(ex1.clone()));
+    println!("{:?}", match_1_char('0')(ex1.clone()));
+    println!("{:?}", match_1_char('1')(ex1.clone()));
+
+    let ex2 = Matchee{
+        matched : string!(""),
+        remained : string!("1234")};
+        println!("~~~{:?}",
+        then_do(then_do(Some(ex2.clone()), &or_do(match_1_char('1'),
+            match_1_char('0'))),&d));
+
+        println!("~~~{:?}",
+            then_do(Some(ex2.clone()),&zero_plus_times_do(&d)));
+
+        println!("~~~{:?}",
+            then!(Some(ex2.clone()),&zero_plus_times_do(&d)));
+        
+        println!("~~~{:?}",
+            then!(Some(ex2.clone()), &d, &d, &d));
+
+
+}
+
+