Simpler way to declare relative precedence

[Charles-Johnson]

How it works now

Currently the 3 concrete concepts prec, default and > are used to declare relative precedence and parse syntax.

prec a is default if no relative precedence is defined for a. Relative precedence if defined like

let (prec a) > prec b

or the precedence can be greater or less than the default precedence

let (prec a) > default

or

let default > prec b

Problems with this approach

• Requires 3 new concrete concepts just for this one feature
• Syntax slightly verbose
• The idea of a default value that a concept implicitly reduces to if it is not known to be greater than or less than anything else is logically difficult to deal with and has led to an awkward implementation

Alternative 1

• Replace the use of let (prec a) > prec b with let a preceed b. Instead of requiring prec and > as concrete concepts, only one, preceed is needed
• Can define concepts with minimum precedence:

  let ((_x_ exists_such_that) let preceed _x_) -> false

Without the default concept it will be tedious to write any syntax because a sufficient number of precedence relations will be needed to be defined for each concept by the user.

Alternative 2

• a preceed b can be syntactic sugar for (prec a) > prec b with

  let (_x_ preceed _y_) -> (prec _x_) > prec _y_

  so preceed doesn't need to be a concrete concept.

• Whenever a new concept is referenced in a let command, if there is ambiguity in the grouping of the syntax and explicitly, in the sense that it will be stored in the snapshot, setting the new concept's precedence as default will resolve this ambiguity then the new concept's precedence will be set as default

This should not make the user's experience more tedious like Alternative 1 and will maintain a useful property of the interpreter that no decision based on something not being known or not (this will help an advanced cache invalidation and the future module system)