Ohm declarative binding syntax

gistfile1.txt

// `ident <- env` means parse an identifier only if it exists in env.
Expr<env>
  = LetExpr<env>
  | WhereExpr<env>
  | ident <- env

LetExpr<env>
  = "letseq" LetSeqBindingsAndBody<env>
  | "letrec" LetRecBindingsAndBody<env>
  | "letpar" LetParBindingsAndBody<env>

// `ident -> env'` means parse an identifier, and add it to a new environment
// named `env'` which delegates to `env`.
LetSeqBindingsAndBody<env>
  = ident -> env' "=" expr<env> "," LetSeqBindingsAndBody<env'>
  | ident -> env' "=" expr<env> "in" Expr<env'>

LetRecBindingsAndBody<env>
  = ident -> env' "=" expr<env'> "," LetRecBindingsAndBody<env'>
  | ident -> env' "=" expr<env'> "in" Expr<env'>

LetParBindingsAndBody<env>
  = ident -> env' "=" expr<env> "," LetParBindingsAndBody<env>  // Uh oh, env' is never passed on...
  | ident -> env' "=" expr<env> "in" Expr<env'>

WhereExpr<env>
  = Expr<env'> "where" WhereSeqBindings<env>  // This also doesn't work, as Expr needs the env produced by the deepest invocation of WhereSeqBindings

WhereSeqBindings = ...