June 2018 Update

Task/Parsing-Shunting-yard-algorithm/Julia/parsing-shunting-yard-algorithm.julia

@@ -0,0 +1,41 @@
+function parseinfix2rpn(s)
+    outputq = []
+    opstack = []
+    infix = split(s)
+    for tok in infix
+        if all(isnumber, tok)
+            push!(outputq, tok)
+        elseif tok == "("
+            push!(opstack, tok)
+        elseif tok == ")"
+            while !isempty(opstack) && (op = pop!(opstack)) != "("
+               push!(outputq, op)
+            end
+        else # operator
+            while !isempty(opstack)
+                op = pop!(opstack)
+                if Base.operator_precedence(Symbol(op)) > Base.operator_precedence(Symbol(tok)) ||
+                   (Base.operator_precedence(Symbol(op)) ==
+                     Base.operator_precedence(Symbol(tok)) && op != "^")
+                    push!(outputq, op)
+                else
+                    push!(opstack, op)  # undo peek
+                    break
+                end
+            end
+            push!(opstack, tok)
+        end
+        println("The working output stack is $outputq")
+    end
+    while !isempty(opstack)
+        if (op = pop!(opstack)) == "("
+            throw("mismatched parentheses")
+        else
+            push!(outputq, op)
+        end
+    end
+    outputq
+end
+
+teststring = "3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3"
+println("\nResult: $teststring becomes $(join(parseinfix2rpn(teststring), ' '))")