Simple JSON parser for Io

JsonParser.io

/*
 * JsonParser.io
 * A simple JSON parser for Io
 * Copyright (c) 2008 Justin Poliey <jdp34@njit.edu>
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * Usage:
 *
 *   obj := JsonParser clone setJson("json_data") parse
 *   obj := JsonParser clone with("json_data") parse
 *   obj := "json_data" parseJson
 *
 */

/* Reference Regex addon */
Regex

/* The JSON parser object */
JsonParser := Object clone do(

	/* The raw JSON data */
	json ::= "{}"
	
	/* Position of the character scanner */
	scan := 0
	
	/* Return n characters at the current position */
	peekToken := method(n,
		n = n ifNilEval(1)
		return if(scan + n < json size, json exSlice(scan, scan + n), nil)
	)
	
	/* Moves the scanner forward n characters */
	nextToken := method(n,
		scan = scan + n ifNilEval(1)
		return(peekToken)
	)
	
	/* Raises an error when expecting a character */
	expectToken := method(ch,
		if(ch != peekToken, Exception raise("'#{peekToken}' at #{scan} found, but expected '#{ch}'" interpolate))
	)
	
	/* Skip whitespace */
	eat := method(
		whitespace := list("\n", "\r", "\t", " ")
		while(whitespace contains(peekToken), nextToken)
	)
	
	/* Convenience method */
	with := method(rawjson,
		setJson(rawjson)
	)
	
	/* Parses JSON and returns an Io representation */
	parse := method(
		eat
		if(peekToken == "{", return readObject)
		if(peekToken == "[", return readArray)
		if(peekToken == "\"", return readString)
		if(peekToken matchesRegex("[0-9\\+\\-]"), return readNumber)
		if(peekToken == "t", return readTrue)
		if(peekToken == "f", return readFalse)
		if(peekToken == "n", return readNull)
		if(peekToken == "/", readComment; return parse)
		Exception raise("Malformed JSON")
	)
	
	/* Skip over a comment */
	readComment := method(
		nextToken
		if(peekToken == "*",
			nextToken
			while(peekToken(2) != "*/",
				nextToken
			)
			nextToken(2)
			return
		)
		if(peekToken == "/",
			while(list("\n", "\r") contains(peekToken) not,
				nextToken
			)
			return
		)
	)
	
	/* Look for a specific literal value */
	readLiteral := method(literal,
		if(peekToken(literal size) == literal,
			nextToken(literal size)
			return true
		,
			return false
		)
	)
	
	/* Returns a boolean true from JSON */
	readTrue := method(
		if(readLiteral("true"), return true, Exception raise("Invalid literal"))
	)
	
	/* Returns a boolean false from JSON */
	readFalse := method(
		if(readLiteral("false"), return false, Exception raise("Invalid literal"))
	)
	
	/* Returns a null value from JSON */
	readNull := method(
		if(readLiteral("null"), return nil, Exception raise("Invalid literal"))
	)
	
	/* Reads a string in JSON format */
	readString := method(
		result := Sequence clone asMutable
		nextToken /* skip initial quote */
		while(peekToken != "\"",
			if(peekToken == "\\",
				nextToken
				if(peekToken == "u",
					nextToken
					result append(peekToken(4) fromBase(16))
					nextToken(4)
				,
					result appendSeq("\\") appendSeq(nextToken)
				)
			,
				result appendSeq(peekToken)
				nextToken
			)
		)
		nextToken
		return(result unescape)
	)
	
	/* Reads a number in JSON format */
	readNumber := method(
		result := Sequence clone asMutable
		while(peekToken matchesRegex("[0-9\\+\\-e]"),
			result appendSeq(peekToken)
			nextToken
		)
		return result asNumber
	)
	
	/* Reads an object in JSON format */
	readObject := method(
		result := Object clone
		loop(
			/* Read a key, enforce it being a string */
			nextToken
			eat
			/* Allow empty objects */
			if(peekToken == "}", nextToken; break)
			key := parse
			if(key type != "Sequence", Exception raise("JSON object keys must be strings"))
			/* Key/value pairs are colon separated */
			eat
			expectToken(":")
			nextToken
			eat
			value := parse
			result setSlot(key, value)
			/* Either end object or get next pair */
			eat
			if(peekToken == "}", break)
			expectToken(",")
		)
		nextToken
		return result
	)
	
	/* Reads an array in JSON format */
	readArray := method(
		result := List clone
		loop(
			/* Read a value */
			nextToken
			eat
			value := parse
			result append(value)
			/* Add another value or end array */
			eat
			if(peekToken == "]", break)
			expectToken(",")
		)
		nextToken
		return result
	)

)

/* A useful method to make an object from a sequence */
Sequence parseJson := method(
	json := JsonParser clone setJson(self) parse
)