Awesome

Paskell

A (reduced) Pascal compiler in Haskell that compiles to LLVM

• Paskell
  • Features
  • Progress
  • Usage
  • Demo
  • Building
    • With docker
    • Without docker
  • Tests
  • Implementation
  • TODO
  • Contributions
  • References

Features

• Declarations: var, type (aliases)
• Types: integer, boolean, string, char, real
• Control Flow: if, while, for
• Functions/Procedures
• Pass by reference
• Basic Typecasting
• Nested Functions/Procedures (Not finished yet)
• I/O: Write/Writeln

Progress

• Lexing/Parsing
• Semantic Analysis/Type-Checking
• Type-Annotated IR AST
• IR pretty-printer
• LLVM Code generation

Usage

Once the executable is built, it can be used to compile Pascal source files to llvm-ir, or internal IR used by the compiler:

paskell -c src compile to llvm-ir
paskell -c src dest compile to llvm-ir and save in dest
paskell -ir src produce internal IR
paskell -x src execute pascal source. Equivalent to paskell -c src | lli
paskell -h (for help)

Demo:

The compiler is complemented with the llvm utilities

$ paskell -c fib.pas fib.ll

Since the output is llvm-ir, we can leverage the many tools LLVM provide to:

• execute it using the llvm interpreter
  $ lli fib.ll
• convert it to bitcode llvm assembly (.bc)
  $ llvm-as fib.ll -o fib.bc
• optimize the code using various settings, for example
  $ opt -mem2reg fib.bc
• translate it to a native assembly executable of a specific architecture (x86, ARM, etc)
  $ llc -march=x86-64 fib.bc -o fib.s
• link many modules into one program

Building

With docker

$ make bash

to build the compiler and launch a shell session where the compiler and llvm utitlies are in $PATH and ready out-of-the-box.

Alternatively

$ make build

will build the same image tagged paskell which can be used with docker run and volumes. For example:

$ docker run -v /path/to/original_file.pas:/path/to/file.pas paskell paskell -c /path/to/file.pas

Without docker

You need to have llvm installed

$ sudo apt-get install llvm-5.0

lli should be in $PATH to be able to execute Pascal programs

Then, you can use Cabal or Stack.
To build using Cabal:

$ cd Paskell/
$ cabal install -j

this will install all dependencies and produce an executable in dist/build/Paskell/

You can also build using Stack.

Tests

$ make test

to run the test suite using docker.

Implementation

This is a 4-pass compiler:

pass 1: lex/parsing
pass 2: type checking
pass 3: constructing IR: type-annotation, type resolution, (future: identifier-renaming, nested-function extraction)
pass 4: code generation

TODO

• finish nested functions/procedures:
  this only requires pulling nested functions to global scope
  and renaming them during the type-annotation pass
• constants: trivial to implement
• Read/Readln IO statements
• records
• arrays
• case statements
• forward declaration

Contributions

Bug reports, added features, etc are welcome

References

• Language grammar
• Stephen Diehl's Haskell llvm-tutorial