More json sketching.

sketching/november_2025/json.dm

@@ -1,21 +1,21 @@
 ns jsonexample
 
 fn main()
-    let rawJson: String = match io::readFile("myDoc.json")
+    let o: obj = match parseJsonObj('{ "a": { "b": { "c": [42] }} }')
-        Success(s) => s,
-        Failure(err) => exit(err)
-    end
-    let o: obj = match parseJsonObj(rawJson)
         Success(o) => o,
-        Failure(err) => exit(err)
+        Failure(err) => panic!("There was an error during Json parsing: ${err}")
     end
     assertEq!(o.a.b.c[0], 42)
 end
 
-fn parseJsonObj(s: String) -> obj
+fn parseJsonObj(s: String) -> Result<obj, JsonParseError>
     let lexer = JsonLexer(s)
     let parser = JsonParser(lexer)
+    try
         parser.object()
+    catch (parseError: JsonParseError)
+        Failure(parseError)
+    end
 end
 
 enum JsonToken
@@ -29,20 +29,58 @@ enum JsonToken
     Boolean(Boolean)
 end
 
-class String
+platform class String
-    pub fn <R> matchAt(startIndex: Int, matchers: Map<Regex, R | fn (match: String) -> R), opts: obj {
+    pub fn <R> matchAt(startIndex: Int, matchers: Map<Regex, R | fn (match: String) -> R), opts: obj + { ignoreWhitespace: Boolean }) -> Option<R>
-        ignoreWhitespace: boolean,
+        let slice: String = if opts.ignoreWhitespace then
-        endIndex: Int
+            /[\t\n\r ]*(<rest>.*)/.match(self[startIndex..]).rest as String
-    }) -> Option<R>
+        else
-        todo!()
+            self[startIndex..]
         end
+        for [regex, result] in matchers do
+            if regex.test(slice) is Some(match) then
+                if result is Fn then
+                    Some(result(match))
+                else
+                    Some(result)
+                end
+            end
+        end
+        None
+    end
+end
+
+platform class Regex
+
+    int RegexMatchBase
+        val match: String
+        val groups: [String],
+        val namedGroups: Map<String, String>
+    end
+
+    pub int RegexMatch
+        props!::<RegexMatchBase>()
+    end
+
+    platform fn doMatch(s) -> Option<RegexMatchBase>
+
+    pub fn match(s: String) -> Option<obj : RegexMatch>
+        doMatch(s).map { base ->
+            dyn obj {
+                ...base,
+                propertyMissing: { name: String ->
+                    base.namedGroups.get(name).unwrap()
+                }
+            }
+        }
+    end
+
 end
 
 class JsonLexer(val source: String)
     var index: Int
 
-    pub fn nextToken() -> Option<JsonToken>
+    fn matchCurrent() -> Option<JsonToken>
-        let token: Option<JsonToken> = source.matchAt(index, [
+        source.matchAt(index, [
             /\{/ => JsonToken::LBrace,
             /}/ => JsonToken::RBrace,
             /\[/ => JsonToken::LSquare,
@@ -52,26 +90,49 @@ class JsonLexer(val source: String)
             /false/ => JsonToken::False(false),
             // The following is not a good way for matching strings but whatever
             /"%w*"/ => { stringWithQuotes => JsonToken::String(stringWithQuotes[1..-1]) }
-        ], ignoreWhitespace: true)
+        ], obj { ignoreWhitespace: true })
-        match token?
+    end
-            JsonToken::LBrace | JsonToken::RBrace | JsonToken::LSquare | JsonToken::RSquare | JsonToken::Comma => do index++ end
+
+    pub fn nextToken() -> Option<JsonToken>
+        matchCurrent().ifSome { token ->
+            match token
+                JsonToken::LBrace | JsonToken::RBrace | JsonToken::LSquare | JsonToken::RSquare | JsonToken::Comma => index++,
                 JsonToken::String(s) => index += s.len() + 2,
                 JsonToken::Number(n) => index += n.toString().len(),
                 JsonToken::Boolean(b) => match b
-                true => do index += 4 end
+                    true => index += 4,
-                false => do index += 5 end
+                    false => index += 5,
                 end
             end
-        token
+        }
     end
+
+    pub fn peek() -> Option<JsonToken> alias matchCurrent
 end
 
 class JsonParser(val lexer: JsonLexer)
 
+    macro parseError!($message)
+        throw JsonParserError($message)
+    end
+
     macro expect!($tokenType)
         match lexer.nextToken()
-            Some(JsonToken::$tokenType) => do end,
+            Some(token) => match token
-            _ => panic! "Expected ${$tokenType}"
+                JsonToken::$tokenType => do end,
+                _ => parseError!("Expected ${$tokenType}")
+            end,
+            _ => parseError!("Expected ${$tokenType}")
+        end
+    end
+
+    macro peek!($tokenType)
+        match lexer.peek()
+            Some(token) => match token
+                JsonToken::$tokenType => true,
+                _ => false
+            end,
+            None => false
         end
     end
 
@@ -86,29 +147,65 @@ class JsonParser(val lexer: JsonLexer)
     end
 
     fn keyValue() -> Option<(String, Any)>
-        let key = match lexer.nextToken()
+        let key = match lexer.peek()
-            Some(JsonToken::String(s)) => s,
+            Some(token) => do
-            _ => return None
+                match token
+                    JsonToken::String(s) => s,
+                    _ => parseError!("Expected String")
+                end
+            end,
+            _ => do return None end
         end
         let value = value()
         Some((key, value))
     end
 
     fn value() -> Any
-        match lexer.nextToken()
+        match lexer.peek()
             Some(token) => match token
+                JsonToken::LBrace => object(),
+                JsonToken::LSquare => array(),
+                _ => do
+                    match lexer.nextToken()
                         JsonToken::String(s) => s,
                         JsonToken::Number(n) => n,
                         JsonToken::Boolean(b) => b,
-                JsonToken::LBrace => object(),
+                        _ => parseError!("Expected String, Number, or Boolean")
-                JsonToken::LSquare => array()
+                    end
+                end
+            end,
+            None => parseError!("Expected LBrace, LSquare, String, Number, or Boolean")
+        end
+    end
+
+    fn array() -> [Any]
+        expect!(LSquare)
+        let results: List<Any> = []
+        while true do
+            match lexer.peek()
+                Some(token) => match token
+                    JsonToken::LBrace => results << object(),
+                    JsonToken::LSquare => results << array(),
+                    _ => do
+                        match lexer.nextToken()
+                            JsonToken::String(s) => results << s,
+                            JsonToken::Number(n) => results << n,
+                            JsonToken::Boolean(b) => results << b,
+                            _ => parseError!("Expected String, Number, or Boolean")
+                        end
+                    end
                 end,
                 None => panic! "Expected LBrace, LSquare, String, Number, or Boolean"
             end
+            match lexer.nextToken()
+                Some(token) => match token
+                    JsonToken::Comma => continue,
+                    JsonToken::RSquare => break
                 end
-
+                _ => panic! "Expected Comma or RSquare"
-    fn array() -> Array<Any>
+            end
-        todo!()
+        end
+        expect!(RSquare)
     end
 
 end