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; [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
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
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