add matchRange

[uann] / src / index.ts

diff --git a/src/index.ts b/src/index.ts
index 3c3384d520bc8bf8d6e54bd6f00bbf47cf909ee2..26cd10df0e081ec2ce445b72c26aeef17bdde0bb 100644 (file)
--- a/src/index.ts
+++ b/src/index.ts
@@ -45,6 +45,36 @@ export function match1Char(c : string) : (m: MatcheePair) => Maybe<MatcheePair>
     }
 };
 
+/**
+ * @description
+ * it returns a function which test if the first char of the `remained` part of
+ *  the argument of the function is between `l` and `u`, if it's true, update the `MatchedPair` wrapped
+ * in `Some`. Otherwise, it returns `None`.
+ *  * @param l : lower bound char, 1-char string
+ *  * @param u : upper bound char, 1-char string
+ * @returns the updated `MatchedPair` wrapped in `Some(x)` or `None`.
+ */
+export function matchRange(l : string, u : string) : (m: MatcheePair) => Maybe<MatcheePair> {
+    let lCodepoint = charToCodepoint(l);
+    let uCodepoint = charToCodepoint(u);
+    if (l > u){
+        throw new Error("Error: the codepoint of `"+l+"` is not smaller than `"+u+"`)");
+    }
+    return (m : MatcheePair)=>{
+
+        const charToBeMatched = m.remained[0];
+        const codePointToBeMatched = charToCodepoint(charToBeMatched);
+        if (codePointToBeMatched >= lCodepoint && codePointToBeMatched <= uCodepoint){
+            return {_tag: "Some", value :{
+                    matched : m.matched + charToBeMatched,
+                    remained : m.remained.substring(1)}};
+        }
+        else{
+            return {_tag: "None"};
+        }
+    }
+};
+
 /**
  * convert the one-char string to codepoint.
  * @param s : the string to code point.