A Type Language for Blockly

Google’s Blockly library provides rudimentary support for types that constrain how blocks can be connected to form larger fragments. We argue that Blockly’s current type language does not reach beyond the level of context-freeness, and show how this can be changed — in a non-disruptive way — by adopting elements from attribute grammar and constraint-based typing. We demonstrate the generality of our approach by applying it to different languages, and describe our implementation and integration into Blockly.