expressionParser

What is this repository about?

This repository contains an F# module with a parser based on the FParsec library that is a study of how to program a parser capable to accept complex mathematical expressions.

The focus of this repo is the clarity of how to approach the parsing process. The resulting parser has no specific productive purpose.

Features of the parser are as follows:

Operands

For simplicity reasons only 'a' and 'b' are allowed.

Operators

• Prefix operators (for simplicity reasons one or more characters from "-~#")
• Postfix operators (for simplicity reasons one or more characters from "!'/")
• Infix operators (for simplicity reasons one or more characters from "+-*/")
• Note: operator character sets may overlap
• Whitespace‑sensitive operator disambiguation control
• Multi‑character operators like ++, --, !=, <= allowed

Expressions

• Expressions can be separated by infix operators.
• Parenthesized expressions are e.g "(a + b)" are allowed
• Terms can have coordinates "a[...]", each coordinate beeing an expression.
• Terms can have arguments "a(...)", each argument beeing an expression.

AST

Each input is transformed into an ast.

Other features

• Debugging the parser possible
• Inbuild operator precedence (prefix > postfix > infix)
• Full whitespace control

Usage and testing

// parse "a"
// parse "a(b,a)"
// parse "a[b,a]"
// parse "b[(a + b!)   ,   -b',a(b) ,b, a]"
// parse "a(-b ,~a)"
// parse "(a )"

let res parse "~a(b)[a, b!]' + b"
printfn "%O" res

// output
Success: Infix
  (Postfix (Prefix ("~", Coord (Call (A, [B]), [A; Postfix (B, "!")])), "'"),
   "+", B)