; [pl0.sty] Grammar "pl0" - a toy language

Language pl0

Regular Grammar

  ign Ign         = ' \n\r'               ; "white" characters
  tok Tok         = ',<=()+-*/'           ; one character tokens
  tok Int         = ('0'..'9')+           ; Integer
  tok Ide         = ('a' .. 'z')+         ; Identifier and Keywords
  com Com         = "#" {"\20" .. "\7e"}  ; Comments

Context Free Grammar

start Program
:pgm: Dfns Runs

let Dfn
:fun: "fun" Ide "(" Args ")" "=" Exp

let Run
:run: "run" Exp

let Exp  :ign0: Exp1
:if  : "if" Exp1 "then" Exp "else" Exp
:exp : "let" Ide "=" Exp ; Assignment

let Exp1 :ign0: Exp2
:les : Exp2 "<" Exp2
:equ : Exp2 "=" Exp2

let Exp2 :ign0: Exp3
:add : Exp2 "+" Exp3
:sub : Exp2 "-" Exp3

let Exp3 :ign0: Exp4
:mlt : Exp3 "*" Exp4
:div : Exp3 "/" Exp4

let Exp4
:neg : "-" Exp4          ; Unary minus
:ign0: "(" Exp ")"
:int : Int               ; Literal
:var : Ide               ; Variable
:app : Ide "(" Exps ")"  ; Application

; Lists

let Args
:nil :
:cons: Ide Args0
let Args0
:nil :
:cons: "," Ide Args0

let Exps
:nil :
:cons: Exp Exps0
let Exps0
:nil :
:cons: "," Exp Exps0

let Dfns
:nil :
:cons: Dfn Dfns

let Runs
:nil :
:cons: Run Runs