IMO the "not equals" is easy to misinterpret as permitting the tree. I think something like this would clearer: Expr = 'number' | '(' Expr '

IMO the "not equals" is easy to misinterpret as permitting the tree. I think something like this would clearer: Expr = 'number' | '(' Expr ')' | Expr '+' Expr (bind-order: 2, assoc: left) | Expr '-' Expr (bind-order: 2, assoc: left) | Expr '*' Expr (bind-order: 1, assoc: left) | Expr '/' Expr (bind-order: 1, assoc: left) or if you want relative precedences: Expr = 'number' | '(' Expr ')' | Expr '+' Expr (add, assoc: left) | Expr '-' Expr (sub, assoc: left) | Expr '*' Expr (mul, assoc: left) | Expr '/' Expr (div, assoc: left) bind-order: mul equals div add equals sub mul before add or if you want to completely separate conflict resolution (and shorter bind-order syntax, and raise a syntax error if certain operators are mixed...this one I like the most): Expr = 'number' | '(' Expr ')' | Expr '+' Expr (add) | Expr '-' Expr (sub) | Expr '*' Expr (mul) | Expr '/' Expr (div) | Expr '&&' Expr (land) | Expr '||' Expr (lor) | Expr '==' Expr (eq) | Expr '!=' Expr (ne) | Expr '.' Expr (haskellDot) | Expr '..=' Expr (range) assoc: left: add, sub, mul, div, land, lor, eq, ne right: haskellDot forbid: range bind-order: mul | div add | sub range eq | ne land | lor haskellDot forbid: eq | ne land | lor