Re: [stack] Flat sublanguages of concatenative languages

Languages of course have all sorts of syntactic and semantic properties.
One useful kind of question to ask is this: which properties of a given
language
are inherited by all of its sublanguages? or of its superlanguages?

Suppose X, Y, Z are languages, X is a sublanguage of Y, and Y is a
sublanguage
of Z. One might write this as X <= Y <= Z.

Now suppose P is a property of Y. Does X have P? Does Z have P? For some
properties P there will be a clear answer. Some properties are ³inherited
downwards², from Y to X. Some properties are ³inherited upwards², fro Y to
Z. From what I can determine, the downwards inherited properties are always
restrictions (good or bad) of some sort. The upwards inherited properties
are the opposite, and I cannot think of a single word which captures what I
mean. Some trivial syntactic properties:

Downwards: ³the letter ³e² is not allowed in identifiers²
Upwards: ³A line of code may contain up to 255 bytes²

Some  semantic ones:

Down: ³integers may not exceed 16 bits²
Up: ³Array subscripts may be up to 32 bits²

Now let X, Y, Z be concatenative languages. Let P be ³is flat².
Given the flatness of Y, can we infer anything about the flatness
of X or of Z? My immediate reaction would be ³of course X will be
flat² and ³we can¹t say anything about the flatness of Z². But
I have learnt to mistrust my immediate reactions. Any views?

  - Manfred


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