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<div class="elementToProof"><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0 elementToProof">Dear Mercury users,<br>
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<div class="elementToProof"><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0"><br>
</span></div>
<div class="elementToProof"><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">Is there any way to write a function that takes a predicate and
returns a transformed predicate without (a) naming a new predicate or (b) using a lambda? In practice, I would like to move the lambda to a function. However, the following code gives an error: "Cannot unify two terms of type `(pred float)'". Can I assume
that this is outside of Mercury's mode system?</span></div>
<div class="elementToProof"><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0"><br>
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<div class="elementToProof"><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">Sincerely, Mark.</span></div>
<div class="elementToProof"><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0"><br>
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<div class="elementToProof"><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">-----</span></div>
<div class="elementToProof"><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0"><br>
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<div class="elementToProof"><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0 ContentPasted1">:- module tests.
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<div class="FluidPluginCopy ContentPasted1">:- interface.</div>
<div class="FluidPluginCopy ContentPasted1">:- import_module io.</div>
<div class="FluidPluginCopy ContentPasted1">:- pred main(io::di, io::uo) is det.</div>
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<div class="FluidPluginCopy ContentPasted1">:- implementation.</div>
<div class="FluidPluginCopy ContentPasted1">:- import_module float, ranges, solutions.</div>
<div class="FluidPluginCopy ContentPasted1">:- use_module math.</div>
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<div class="FluidPluginCopy ContentPasted1">main(!IO) :-</div>
<div class="FluidPluginCopy ContentPasted1"> test1(!IO), % OK</div>
<div class="FluidPluginCopy ContentPasted1"> test2(!IO). % Does not compile</div>
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<div class="FluidPluginCopy ContentPasted1">:- pred test1(io::di, io::uo) is det.</div>
<div class="FluidPluginCopy ContentPasted1">test1(!IO) :- </div>
<div class="FluidPluginCopy ContentPasted1"> Data = (pred(Y::out) is nondet :- nondet_member(I,range(1,5)), Y = float(I)), % some data<br>
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<div class="FluidPluginCopy ContentPasted1"> LnData = (pred(Y::out) is nondet :- Data(X), Y = math.ln(X)), % a transformation<br>
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<div class="FluidPluginCopy ContentPasted1"> aggregate(LnData, print_line, !IO).</div>
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<div class="FluidPluginCopy ContentPasted1">:- pred test2(io::di, io::uo) is det.</div>
<div class="FluidPluginCopy ContentPasted1">test2(!IO) :- </div>
<div class="FluidPluginCopy ContentPasted1"> Data = (pred(Y::out) is nondet :- nondet_member(I,range(1,5)), Y = float(I)), % some data<br>
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<div class="FluidPluginCopy ContentPasted1"> LnData = f_ln(Data), %% This transformation does not compile:(<br>
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<div class="FluidPluginCopy ContentPasted1"> aggregate(LnData, print_line, !IO).</div>
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<div class="FluidPluginCopy ContentPasted1">:- func f_ln(pred(float)::(pred(out) is nondet)) = (pred(float)::(pred(out) is nondet)).</div>
<div class="FluidPluginCopy ContentPasted1">f_ln(Pred) = (pred(Y::out) is nondet :- Pred(X), Y is math.ln(X)).</div>
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