order after yield gives 'unbound variable' error

[julianhyde]

order after yield gives 'unbound variable or constructor' error.

For example:

val emps = [
   {id = 100, name = "Fred", deptno = 10},
   {id = 101, name = "Velma", deptno = 20},
   {id = 102, name = "Shaggy", deptno = 30},
   {id = 103, name = "Scooby", deptno = 30}];
from e in emps
  yield {e.name, e.deptno}
  order deptno
unbound variable or constructor: e

[julianhyde]

In this fix, we also clarify the type of from with various clauses.

yield with record returns a record, even if that record has 1 field:

- from i in [1, 2, 3]
=   yield {i};
val it = [{i=1},{i=2},{i=3}] : {i:int} list

yield can also have a scalar value:

from i in [1,2,3]
  yield i mod 3;
val it = [1,2,0] : int list

But if the yield is in the middle of a pipeline, the scalar form is pretty useless; you need a field name in order to be table to use it in the next clause, so use a single-field record:

- from i in [1,2,3]
=   yield {j = i mod 3}
=   order j;
val it = [{j=0},{j=1},{j=2}] : {j:int} list

You can add another yield to convert it back to a scalar:

- from i in [1,2,3]
=   yield {j = i mod 3}
=   order j
=   yield j;
val it = [0,1,2] : int list

[julianhyde]

Fixed in d1c0352.