Winzig-Calc

A simple interpreter that can perform simple calculations.

Still in development.

Note

This project is still in development, so there may be a lot of bugs.

As this is a personal practice project, I may not be able to provide support in time.

Feel free to pull request or issue.

How to use

You can simply use winzig_ez_main(argc, argv) in winzig_calc.c as a repl. Start it and input the allowed expression syntax directly.

Or you can initialize a WinzigCalc object and use winzig_code to evaluate a sourcecode.

you can also try separately use Tokenizer, Parser or Interpreter provided.

Features

• Only one data type: long double
• lots of operators supported
  • calculator: +, -, *, /, ^ ( it's pow )
  • assignment: =, +=, -=, *=, /=
  • logical: &, | ( will return 0 or 1, no short-circuit or lazy evaluation )
  • comparison: ==, !=, <, <=, >, >=
• ( ) to control the priority
• { } block control
• if, else, while statement

Syntax

Statement

<expr>;

The semicolon is optional, but it is recommended. Unlike Rust, the semicolon will not discard the value of the expression.

Assignment

<name> = <expr>;

Assign a value to a variable. The variable name can only be a combination of letters and numbers, and cannot start with a number.

Since there is only one data type, there is no declaration syntax.

Values are stored in a hash table by the hash of the variable name, and there is a small probability of collision. We pre-fill the hash table with qnan and do not check for undefined variables, so please be careful.

Expression

<expr> ::= <term> | <term> <addop> <expr>

Note that we do not have unary operators.

Control Flow

if (<expr:condition>) { <block:body> }
[else { <block:body> }]

Only single-layer if-else statements are supported, else is optional, and there is no else if, you can nest it yourself.

There is no switch-case statement.

Curly braces are optional for single-line blocks.

Loop

while (<expr:condition>) { <block:body> }

There is only one loop statement, while, and no for or do-while.

Curly braces are optional for single-line blocks.

No break or continue statement yet.

Predefined Functions

No user defined functions yet.

For convenience, all functions are unary functions, there are no multi-parameter functions or zero-parameter functions. Please pass one value or one anything when calling a zero-parameter function.

Following functions are predefined:

math functions: sin, cos, tan, asin, acos, atan, sqrt, exp, log, log10, ceil, floor, round. (who can't call a library?)

Our provided functions:

• sign(x) (sign function, return -1, 0, 1)
• boolean(x) (convert to boolean, return 0 or 1)
• print(x) (print a single number and newline, return the number of bytes printed)
• rand(_) (return a random number between 0 and 1)
• input(_) (return the input number, or input q to interrupt the entire program)
• exit(_) (exit the program)

Known Problems

1. evil special judgement in parser.
2. only 1 number type: long double supported
3. a load of bugs hiding in the code. See if you are lucky enough to find one.
4. REPL does not support multi-line input well.

Future Plan

These are also problems, somehow.

Maybe I will solve them when pigs fly. :)

• linter: optimize the code style (possibly mark operators in advance, leaving the tokenizer only to split ' ' and recognize keywords)
• lexer: recognize the operators and keywords , facilitate the parser to judge.
• pre-collect all declaration to save memory, improve speed, and easily report 'NotDefined' error
• improve data structure to save the variable type, add more types: boolean, string, etc.
• string literal
• function grammar
• provide a runner struct everywhere to save all errors and easily report them
• arrayed types
  1. array literal [,] syntax and array access [] syntax
  2. slice, range, and other iterator methods
  3. for-in loop
• constant optimize
  1. when parser found all sub node is Literal, call interpreter to calculate them.