attr_types

attr_types(a)

A macro which returns an attr:type list from relation a, which must contain {attr:str, type:str} and optionally {seq:int}. The attr:type list is built at call-time, i.e. just before the expression in which it is embedded is evaluated. It can be used as a relation constructor, as a relational operator output type declaration, or anywhere an attribute:type list is needed.

If {seq:int} is provided, it will be used as a left-right ordering for places where that matters.

Examples

heading($P)

attr
type

PNO
str
PNAME
str
COLOR
str
WEIGHT
int
CITY
str

attr_types creates a table, a list of tuples (not a relation)

attr_types(heading($P))

#################
  attr     type  
  PNO      str   
  PNAME    str   
  COLOR    str   
  WEIGHT   int   
  CITY     str   
#################

Use as a relation constructor - using only str attributes

{attr_types(heading($P)[type="str"])}{}

CITY
COLOR
PNAME
PNO

route relgen handler - using a dynamic heading copied from http.hh saves a lot of typing

import("http")

index_handler := {attr_types(http.hh)} begin
    response := http.response{*, body := "Hello world, wide web"}
    yield
end