Training Exams for PL

Exam: Parsing RegExps

• Read carefully the pdf with the questions (opens new window)
• Fill the code in this template repo ULL-ESIT-PL/exam-training-template (opens new window)

AST Explorer (opens new window) supports various regexp parsers. Feel free to play with them and have a look at the shapes of the ASTs.

Watch this video

and this other from minute 30:30:

Exam: Parsing JSON

See also another exam example in section Translator from Egg AST to AST Term of the TFA. The task there is to build a JSON Parser and translate a JSON containing the AST of an Egg parser onto the term notation.

Parsing JSON

Question

• Exam Parsing JSON: pdf file. Question: Parse the JSON Language

Examples of Solutions

• Solution: JSON parser in nearley.js (opens new window)
  • Task to do: Improve the solution by using your own lexical analyzer generator instead of the current moo lexer, removing the explicit use of white spaces (syntactic variable _ like in the production rule pair -> key _ ":" _ value) in the Nearley grammar
• Solution: JSON parser in yacc (opens new window)
• Solution: JSON parser in pegjs (opens new window)

Translator from Egg AST to AST Term

Question

Example of a second part for the exam:

Assume the input JSON contains an Egg AST and translate it to AST Term notation.

Here is an example. Given the input program:

➜  evm2term git:(master) cat examples/property.egg 
x["sub", 1]("length") # 3

Whose JSON looks like:

➜  evm2term git:(master) head -n 4 examples/property.json 
{
  "type": "apply",
  "operator": {
    "type": "property",

The output of the evm2term translator will be:

➜  evm2term git:(master) evm2term examples/property.json 
apply(op:property(op:word{x}, args:[value{sub},value{1}]), args:[value{length}])

Possible Improvements if you decide it to present as TFA:

• Add pretty printing of the term
• Give support to JS Esprima ASTs
• Make it generic so that any compiler AST can be added via some configuration

Example of Solution

• See package evm2term (opens new window) and file crguezl/evm2term/index.js (opens new window) for a solution using estraverse