Minimal bytecode compiler for pseudocode

Pre-requisites

• Any C++ compiler

Installation guide for linux

git clone https://github.com/MustafaAamir/pscompiler
cd pscompiler
make
./pscompiler --help

Optional

To enable interactive REPL history, install the GNU-rlwrap utility

dnf install rlwrap

//run pscompiler with rlwrap
rlwrap ./pscompiler --help

To enable/disable lowercase keywords

Open pscompiler/lexer/lexer.h

vi lexer/lexer.h

set lowercase to true

const bool lowercase = true;

Program Features

• REPL
• File execution
• Benchmarking with --benchmark flag
• Tokenization with --lexer flag
• CLI interface
• Minimal GUI

Language features

• I/O statements input Identifier, output Expression
• Conditional Expressions if...then...else

if <Condition> then
    (Statement)*
else
    (Statement)*
endif

• Count-controlled loop for...to...next

declare <Identifier> : integer
for <Identifier> <- <expression> to <expression>
  (Statement)*
next <Identifier>

• Pre-condition loop while...do...endwhile

while <Condition> do
    (Statement)*
endwhile

• Post-condition loop repeat...until

repeat
   (Statement)*
until <Condition>

• Dynamic typing
• type-convertions integer_cast, real_cast, string_cast

integer_cast(<integer> | <real>) -> integer
real_cast(<integer>   | <real>) -> real
string_cast(<integer> | <real> | <char> | <string>) -> string

• 1-D Arrays

declare <Identifier> : array[<lb>:<ub>] of <DataType>

• non-parameterized procedures (experimental)

procedure <Identifier>()
    (Statement)*
endprocedure

builtin functions

• Arithmetic:

sin(<integer>  | <real>) -> real
cos(<integer>  | <real>) -> real
tan(<integer>  | <real>) -> real
sqrt(<integer> | <real>) -> real
abs(<integer>  | <real>) -> integer

-- where lb <= returnvalue <= ub
random_integer(<lb>, <ub>) -> integer
random_real(<lb>, <ub>) -> real

• String Handling

mid(<string>, <startpos>, <length>) -> string
length(<string>) -> string

• Type-casting

integer_cast(<real> | <integer>) -> integer
real_cast(<real> | <integer>) -> real
string_cast(<string> | <char> | <real> | <integer>) -> string

• System

system(<string>)

used to execute system commands

• builtin functions with a single argument can be used without parentheses:

> output sin 1
Output: 0.84147

-- in aggregate
> output sin cos tan sqrt abs length mid("Hello, World!", 0, 5)
Output: 0.287797

-- is equivalent to
> output sin(cos(tan(sqrt(abs(length(mid("Hello, World!")))))))
Output: 0.287797

• However, parentheses are required for builtins with expression arguments:

> output sin 1 + 1
Output: 1.84147

> output sin(1) + 1
Output: 1.84147

> output sin(1 + 1)
Output: 0.909297

• Further demonstration of builtins in examples/builtin_test.pse

Pending features

• Hashmaps: (trivial to implement if std::unorderd_map<Value, Value> is utilized)
• Parameterized procedures & functions: when called CALL Add(1, 2) declares parameters as local variables, pops values off of the value stack and sets them to the respective parameters.
• Recursion
• Static type checking
• Referencing & dereferencing ^Ptr, Ptr^: Ptr of type uint16_t used as index in Chunk::constantPool
• File handling: READFILE, WRITEFILE, OPENFILE, CLOSEFILE

Problems

• Insufficient support for FOR loops. Increment value is +1 by default, therefore only loops going in the positive direction are allowed. Loops in the negative direction could be implemented by adding an addtional LT & GT comparison before the loop commences, and emiting the appropriate comparison operator (LesserEqual || GreaterEqual) based on the result.
• Project architecture needs refactoring. ErrorReporter should be a seperate global entity to ensure configurability, i.e. enabling logging or lowercase lexing via command-line arguments.

Todo

• Increase jumpsize to uint16_t max
• render donut.pse