forked from lix-project/lix
Add primop genList
This can be used to implement functions like ‘imap’ (or for that matter, ‘map’) without the quadratic complexity incurred by calling ‘++’ repeatedly.
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@ -364,6 +364,24 @@ builtins.fromJSON ''{"x": [1, 2, 3], "y": null}''
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</varlistentry>
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<varlistentry><term><function>builtins.genList</function>
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<replaceable>generator</replaceable> <replaceable>length</replaceable></term>
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<listitem><para>Generate list of size
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<replaceable>length</replaceable>, with each element
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<replaceable>i></replaceable> equal to the value returned by
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<replaceable>generator</replaceable> <literal>i</literal>. For
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example,
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<programlisting>
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builtins.genList (x: x * x) 5
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</programlisting>
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returns the list <literal>[ 0 1 4 9 16 ]</literal>.</para></listitem>
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</varlistentry>
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<varlistentry><term><function>builtins.getAttr</function>
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<replaceable>s</replaceable> <replaceable>set</replaceable></term>
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@ -1364,6 +1364,25 @@ static void prim_all(EvalState & state, const Pos & pos, Value * * args, Value &
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}
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/* Apply a function to every element of a list. */
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static void prim_genList(EvalState & state, const Pos & pos, Value * * args, Value & v)
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{
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state.forceFunction(*args[0], pos);
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auto len = state.forceInt(*args[1], pos);
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if (len < 0)
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throw EvalError(format("cannot create list of size %1%, at %2%") % len % pos);
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state.mkList(v, len);
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for (unsigned int n = 0; n < len; ++n) {
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Value * arg = state.allocValue();
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mkInt(*arg, n);
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mkApp(*(v.listElems()[n] = state.allocValue()), *args[0], *arg);
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}
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}
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/*************************************************************
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* Integer arithmetic
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*************************************************************/
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@ -1759,6 +1778,7 @@ void EvalState::createBaseEnv()
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addPrimOp("__foldl'", 3, prim_foldlStrict);
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addPrimOp("__any", 2, prim_any);
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addPrimOp("__all", 2, prim_all);
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addPrimOp("__genList", 2, prim_genList);
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// Integer arithmetic
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addPrimOp("__add", 2, prim_add);
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@ -54,8 +54,8 @@ rec {
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const = x: y: x;
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range = first: last:
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if builtins.lessThan last first
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if first > last
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then []
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else [first] ++ range (builtins.add first 1) last;
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else genList (n: first + n) (last - first + 1);
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}
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