add 2020 and some cleanup

2020/lib/loader.nim

@@ -0,0 +1,20 @@
+import streams, strutils
+
+
+func getFileName(daynum: int, suffix: string = ""): string =
+    if daynum < 10:
+        result = "0"
+    result = "data/" & result & $daynum & suffix & ".txt"
+
+
+proc loadStrings*(daynum: int, suffix: string = ""): seq[string] =
+    var s = openFileStream(getFileName(daynum, suffix))
+    for line in s.lines():
+        result.add(line)
+
+
+proc loadInts*(daynum: int): seq[int] =
+    var s = openFileStream(getFileName(daynum))
+    for line in s.lines():
+        let n = parseInt(line)
+        result.add(n)

2020/lib/util.nim

@@ -0,0 +1,44 @@
+import std/macros
+
+
+macro `<-`*(lhs: untyped, rhs: untyped): untyped =
+    # ensure that the left-hand side is a valid bracket expression e.g. [a, b, c]
+    let errmsg = "Invalid syntax for unpack operator: " & lhs.toStrLit().strVal()
+    if lhs.kind != nnkBracket:
+        error(errmsg, lhs)
+    for name in lhs:
+        if name.kind != nnkIdent:
+            error(errmsg, lhs)
+    
+    # the result will be a check to ensure no index defects, followed by assignment statements
+    result = newNimNode(nnkStmtList, lineInfoFrom = lhs)
+
+    # first add a check to ensure that the container being unpacked has enough values
+    # this has to be done at runtime, since it's potentially unknown at compile time
+    let numIdents = lhs.len
+    let strRepr = lhs.toStrLit().strVal() & " <- " & rhs.toStrLit().strVal()
+    let lenCheck = quote do:
+        if `rhs`.len < `numIdents`:
+            raise newException(ValueError, "Not enough values to unpack: \"" & `strRepr` & "\"")
+    result.add(lenCheck)
+
+    var assign_from = rhs
+    # if the right-hand side is an expression, it might
+    # be expensive, so we save it to a temp variable
+    if rhs.kind != nnkIdent:
+        # repoint assign_src so that we end up using a temp variable
+        # instead of repeating the original expression a bunch of times
+        assign_from = ident("unpack_tmp_src")
+        # e.g. "let unpack_tmp_src = somestring.split()"
+        let declare_assign_src = newLetStmt(assign_from, rhs)
+        result.add(declare_assign_src)
+
+    # finally, inject the actual assignments
+    for i, name in lhs:
+        let assignment = quote do:
+            # expanded to e.g. "let a = someseq[0]"
+            let `name` = `assign_from`[`i`]
+        result.add(assignment)
+
+
+proc showAddr*[T](x: T) = echo cast[uint64](unsafeAddr x)