Questionable math expression grammar.

math.pest

defn =_{ soi ~ variable ~ "=" ~ expr ~ eoi }
main =_{ soi ~ expr ~ eoi }

add = { "+" }
sub = { "-" }
mul = { "*" }
div = { "/" }
rem = { "%" }
exp = { "^" }

atom = { function ~ "(" ~ expr ~ ")"
       | "(" ~ expr ~ ")"
       | float
       | variable
       | "i"
       }
fact = { atom ~ (exp ~ term)? }
join = { fact+ }
term = { (add | sub)* ~ join }
prod = { term ~ ((mul | div | rem) ~ term)* }
expr = { prod ~ ((add | sub) ~ prod)* }

alpha = { 'a'..'z' | 'A'..'Z' }
digit = { '0'..'9' }
float =@{ digit+ ~ ("." ~ digit+)? }

variable =@{ alpha }
function =@{ alpha ~ (alpha | digit)*  }

whitespace = _{ " " }