ENH #52 Implemented parentheses checker.

Author: abalkin

src/Q.jl

@@ -108,5 +108,6 @@ if GOT_Q
 else
     include("client.jl")
 end
+include("parser.jl")
 end # module Q
 include("q-prompt.jl")

src/parser.jl

@@ -0,0 +1,25 @@
+"""
+    balanced(parens) -> checker
+
+The `checker` function returns position of misbalanced parenthesis
+or 0 is the given string is balanced, and -1 if there are more open
+parentheses than closed.
+"""
+function balanced(parens="()[]{}")
+    openers = parens[1:2:end]
+    closers = parens[2:2:end]
+    action = Dict(o => (o, +1) for o in openers)
+    merge!(action, Dict(c => (o, -1) for (o, c) in zip(openers, closers)))
+    init = Dict(zip(openers, zeros(Int, length(openers))))
+    function(cmd::AbstractString)
+        state = copy(init)
+        for (i, x) in enumerate(cmd)
+            x, n = get(action, x, ('x', 0))
+            if x != 'x' && (state[x] += n) < 0
+                return i
+            end
+        end
+        any(x > 0 for x in values(state)) ? -1 : 0
+    end
+end
+const chkparens = balanced()

test/parser-tests.jl

@@ -0,0 +1,8 @@
+import Q: chkparens
+@testset "parser" for (n, cmd) in [
+   (0, "([{}])"),
+   (-1, "([{}]"),
+   (5,  "((([}])))"),
+]
+   @test n == chkparens(cmd)
+end

test/runtests.jl

@@ -16,5 +16,6 @@ const side = GOT_Q ? "server" : "client"
   include("text-tests.jl")
   include("list-tests.jl")
   include("table-tests.jl")
+  include("parser-tests.jl")
   include("$side-tests.jl")
 end