SML
SML
is a simple markup language designed to convert human readable information into Rust
types with a very specific purpose of loading config files and schemas.
The format looks like
hobbit:
name: Frodo Baggins
age: 98
friends:
hobbit:
name: Bilbo Baggins
age: 176
hobbit:
name: Samwise Gamgee
age: 66
Data Format Rules
-
Indentation has meaning and is 4 spaces, relative to the top key. If indenting is relative to the top key, then you can neatly align strings embedded in code.
-
All values must be double quoted.
-
Key/value combinations are used for fields
name: "Frodo"
are used for struct
fields and enum
variants. Keys only
hobbit:
name: "Frodo"
indicate a complete struct
or enum
. In this way, the data clearly indicates the mapping to
Rust data structures.
-
Separation of lines has meaning.
-
Keys must not include but must be followed by a colon
:
. -
Double quotes in values must be escaped using
\"
. -
Everything after the second double quote is ignored.
-
Empty lines or lines with whitespace only are ignored.
-
Comments require
//
at the start of the line for example
// comment
hobbit:
name: "Frodo"
Example. From Small
-formatted string to your data-structure.
This examples should cover 90 percent of use cases.
use ;
FromSmall
Trait
Types that implement the FromSmall
trait can be constructed from a Small
-formatted string.
Required function:
from_small
The from_small()
function describes how to create a data-structure from the parts of
Small
.
path
Reduces Small
to the key_path
and then uses the FromSmall
trait to convert to the
receiver type.
from_str
Top level function that convert a Small
-formatted string into the receiver.
from_str_debug
Top level function that converts a Small
-formatted string into the receiver giving helpful
error messages for debugging.
Implementation
A Small
value may be a collection of Small
values. For example,
hobbit:
name: "Bilbo Baggins"
age: "176"
hobbit:
name: "Samwise Gamgee"
age: "66"
is a collection of two elements
hobbit:
name: "Bilbo Baggins"
age: "176"
and
hobbit:
name: "Samwise Gamgee"
age: "66"
Often when implementing FromSmall
we want to convert a Small
object into a single value, so
we need to check that Small
has only one element The implementation to convert from Small
to u32
gives indicates how to do this. unique_value()
checks that there is only one element
in Small
and if so returns that one element and value()
extracts that value as a String
.