diff --git a/src/problem/JSONParse.jl b/src/problem/JSONParse.jl
index 574ef139..2b803c0e 100644
--- a/src/problem/JSONParse.jl
+++ b/src/problem/JSONParse.jl
@@ -75,36 +75,53 @@ function perf_parse_json(strng::AbstractString)
         if strng[pos] != '"'
             error("AbstractString starting with quotation expected at position $pos")
         else
-            pos = pos + 1
+            pos += 1
         end
-        str = ""
+        str = IOBuffer()
         while pos <= len
             nc = strng[pos]
             if nc == '"'
+                pos += 1
+                return String(take!(str))
+            elseif nc == '\\'
                 pos = pos + 1
-                return string(str)
-            elseif nc ==  '\\'
-                if pos+1 > len
-                    error_pos("End of file reached right after escape character")
-                end
-                pos = pos + 1
+                pos > len && break # goto error handling
                 anc = strng[pos]
-                if anc == '"' || anc == '\\' || anc == '/'
-                    str = string(str, strng[pos])
-                    pos = pos + 1
-                elseif anc ==  'b' || anc == 'f'|| anc == 'n' || anc == 'r' || anc == 't'
-                    str = string(str, '\\', string[pos])
-                    pos = pos + 1
+                if anc ==  '"'
+                    write(str, "\"")
+                    pos += 1
+                elseif anc ==  '\\'
+                    write(str, "\\")
+                    pos += 1
+                elseif anc ==  '/'
+                    write(str, "/")
+                    pos += 1
+                elseif anc ==  'b'
+                    write(str, "\b")
+                    pos += 1
+                elseif anc ==  'f'
+                    write(str, "\f")
+                    pos += 1
+                elseif anc ==  'n'
+                    write(str, "\n")
+                    pos += 1
+                elseif anc ==  'r'
+                    write(str, "\r")
+                    pos += 1
+                elseif anc ==  't'
+                    write(str, "\t")
+                    pos += 1
                 elseif anc == 'u'
-                    if pos+4 > len
-                        error_pos("End of file reached in escaped unicode character")
-                    end
-                    str = string(str, strng[pos-1:pos+4])
+                    pos + 4 > len && break # goto error handling
+                    write(str, Char(parse(Int, strng[pos:pos+4], base=16)))
                     pos = pos + 5
+                else # should rarely happen
+                    write(str, anc)
+                    pos = pos + 1
                 end
-            else # should never happen
-                str = string(str,strng[pos])
-                pos = pos + 1
+            else # common case
+                write(str, nc)
+                pos = nextind(strng, pos)
             end
         end
         error("End of file while expecting end of string")
diff --git a/src/shootout/binary_trees.jl b/src/shootout/binary_trees.jl
index 281341c4..59fdadf4 100644
--- a/src/shootout/binary_trees.jl
+++ b/src/shootout/binary_trees.jl
@@ -4,17 +4,17 @@
 #
 # Ported from an OCaml version
 
-abstract type BTree end
 
-mutable struct Empty <: BTree
-end
+struct Empty end
 
-mutable struct Node <: BTree
-    info
-    left::BTree
-    right::BTree
+struct Node{T}
+    info::T
+    left::Union{Node{T}, Empty}
+    right::Union{Node{T}, Empty}
 end
 
+const BTree{T} = Union{Node{T}, Empty}
+
 function make(val, d)
     if d == 0
         Node(val, Empty(), Empty())
diff --git a/src/shootout/regex_dna.jl b/src/shootout/regex_dna.jl
index 8e519fde..887d6746 100644
--- a/src/shootout/regex_dna.jl
+++ b/src/shootout/regex_dna.jl
@@ -5,30 +5,30 @@
 # Fix from David Campbell
 
 const variants = [
-      "agggtaaa|tttaccct",
-      "[cgt]gggtaaa|tttaccc[acg]",
-      "a[act]ggtaaa|tttacc[agt]t",
-      "ag[act]gtaaa|tttac[agt]ct",
-      "agg[act]taaa|ttta[agt]cct",
-      "aggg[acg]aaa|ttt[cgt]ccct",
-      "agggt[cgt]aa|tt[acg]accct",
-      "agggta[cgt]a|t[acg]taccct",
-      "agggtaa[cgt]|[acg]ttaccct"
+      r"agggtaaa|tttaccct",
+      r"[cgt]gggtaaa|tttaccc[acg]",
+      r"a[act]ggtaaa|tttacc[agt]t",
+      r"ag[act]gtaaa|tttac[agt]ct",
+      r"agg[act]taaa|ttta[agt]cct",
+      r"aggg[acg]aaa|ttt[cgt]ccct",
+      r"agggt[cgt]aa|tt[acg]accct",
+      r"agggta[cgt]a|t[acg]taccct",
+      r"agggtaa[cgt]|[acg]ttaccct"
 ]
 
-const subs = [
-    (r"B", "(c|g|t)"),
-    (r"D", "(a|g|t)"),
-    (r"H", "(a|c|t)"),
-    (r"K", "(g|t)"),
-    (r"M", "(a|c)"),
-    (r"N", "(a|c|g|t)"),
-    (r"R", "(a|g)"),
-    (r"S", "(c|g)"),
-    (r"V", "(a|c|g)"),
-    (r"W", "(a|t)"),
-    (r"Y", "(c|t)")
-]
+const subs = (
+    ("B" => "(c|g|t)"),
+    ("D" => "(a|g|t)"),
+    ("H" => "(a|c|t)"),
+    ("K" => "(g|t)"),
+    ("M" => "(a|c)"),
+    ("N" => "(a|c|g|t)"),
+    ("R" => "(a|g)"),
+    ("S" => "(c|g)"),
+    ("V" => "(a|c|g)"),
+    ("W" => "(a|t)"),
+    ("Y" => "(c|t)")
+)
 
 function perf_regex_dna()
     infile = joinpath(SHOOTOUT_DATA_PATH, "regexdna-input.txt")
@@ -38,20 +38,29 @@ function perf_regex_dna()
     seq = replace(seq, r">.*\n|\n" => "")
     l2 = length(seq)
 
+    kk = 0
     for v in variants
         k = 0
-        for m in eachmatch(Regex(v), seq)
+        for m in eachmatch(v, seq)
             k += 1
         end
-#        @printf("%s %d\n", v, k)
+        kk += k
     end
 
-    for (u, v) in subs
-        seq = replace(seq, u => v)
+    try
+        # VERSION > 1.7-dev
+        seq = replace(seq, subs...)
+    catch ex
+        ex isa MethodError || rethrow()
+        # semi-optimized regex
+        r = Regex(join(first.(subs), "|"))
+        repl = Dict(subs)
+        seq = replace(seq, r => (r -> repl[r]))
+        ## multiple passes
+        #for sub in subs
+        #    seq = replace(seq, sub)
+        #end
     end
 
-#    println()
-#    println(l1)
-#    println(l2)
-#    println(length(seq))
+    seq, kk
 end