w1 ₃₂→₁₆ w2

[mn200]

Make it so. Depends on #499

[mn200]

Actually, casts are unary, so perhaps we could have this as a suffix, so that

     w1 ₃₂→₁₆

would be the 16 bit value corresponding to w1.

Alternatively, and this is the one that Magnus prefers, have

        ₃₂←₁₆ w2

which would be the 32 bit version of (16 bit value) w2.

[konrad-slind]

Possibly naive question. Why not have a general operation

width(w,n)

which maps word w to its corresponding n-width version? Being binary, the "width" operation could even be an infix, although I am not sure that you are even considering concrete syntax.

On Tue, Jan 7, 2020 at 10:01 PM Michael Norrish notifications@github.com wrote:

Actually, casts are unary, so perhaps we could have this as a suffix, so that

 w1 ₃₂→₁₆

would be the 16 bit value corresponding to w1.

Alternatively, and this is the one that Magnus prefers, have

    ₃₂←₁₆ w2

which would be the 32 bit version of (16 bit value) w2.

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[mn200]

You actually need to know both source and destination sizes, so in some sense it's a ternary operation. Moreover, the source and dest numbers have to be literals; they're not really arguments in the way that the w is.

(This is all supposing that we have words of arbitrary widths floating around (as per issue #499).)

[konrad-slind]

Right. I was operating under the assumption that w would have a type from which its size could be calculated. (I did this in a language we worked on at Collins. Yes, the target width was a literal.)

On Tue, Jan 7, 2020 at 11:22 PM Michael Norrish notifications@github.com wrote:

You actually need to know both source and destination sizes, so in some sense it's a ternary operation. Moreover, the source and dest numbers have to be literals; they're not really arguments in the way that the w is.

(This is all supposing that we have words of arbitrary widths floating around (as per issue #499 https://github.com/CakeML/cakeml/issues/499 ).)

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