Type driven code suggestions

In this project we provide a proof of concept for generating code suggestions for invalid programs.

In short: we take some invalid code and see what the minimum* number of changes is to make it type check and thus compile.

to do this we implemented these suggestions for a small subset of haskell

as an example take:

plus :: Int -> Int -> Int
stringRepeat :: Int -> String -> String

fun = stringRepeat "hello " plus 3 5)

we can generate the following suggestion:

did you mean:
fun = stringRepeat (plus 3 5) "hello "
--diff:--
fun = stringRepeat (str plus 3 5) str
--Which has type: String

this is meant as an addition to the normal error messages

this algorithm is able to recognise missing/misplaced brackets and flip arguments. As the title suggests these are generated based on the type system so we know that the final suggestion will type check.

features currently supported:

• fixing brackets
• swapping arguments
• lambda functions

Key insights and assumptions

We assume that most programmers only make a few mistakes at a time. So we need to generate suggestions for mostly correct code.

A key insight is to split the code into sections early so we can fail late. While one function may not even get trough the parser we continue with the functions that do work. This allows us to get type information on the working functions wich can then be used to generate the suggestions.

Another key idea is to use the types the programmer gives to guide the suggestion generation.

how to build

Open a terminal in the base directory and run:

cabal install alex

Then reboot the terminal (don't know if this is nessecairy). Then run

cabal clean
cabal build

finally to run the program

cabal run

use

cabal test

to run the test cases.

A bunch of examples:

TODO: add a bunch of examples here.