custom precedence rules

10.6: adda/syntax/prec'order:

. unlike the etree parser

where precedence was table-driven,

adda must know precedence also by type;

and then each type can additionally provide

a prec'table that can reduce the need for writing paren's .

. how does a type`declaration specify precedence?

it can list the symbols in groups of

{values, uniop's, biop's, others},

and then under biop's,

the order given is also the prec'order .

. do the highest precedence last,

so they are listed in the same order they would be

in a parse tree

when no paren's are involved; eg:

( +, -

; *, /

; ** ).

[10.9: just noticed some biop's will have equal precedence,

so there needs to be both comma's and semi-colons

to distinguish equal from unequal levels ] .

override:

. a place where paren's need be part of parse.tree

is explicit paren's when none is needed?

but still don't need a paren' op[etree symbol for explicit paren's],

rather, when paren's are optional yet user-preferred,

use multiple operations vs a single multiarg operation:

eg,

a+b+c: +(a,b,c),

vs:

a+(b+c): +(a, +(b,c)),

[10.9:

. must consider not only user's preference,

but also how eval' order of numbers can affect precision .]