Adds starting point for patterns code

Author: apblack

patterns/patterns.grace

@@ -0,0 +1,68 @@
+dialect "minispec"
+
+describe "pattern construction" with {
+    specify "star" by {
+        expect (pattern "*".asString) toBe "(star Token)"
+    }
+    specify "* ABC *" by {
+        expect (pattern "*ABC*".asString) toBe "(star Token)(ABC Token)(star Token)"
+    }
+    specify "* ABC * XYZ *" by {
+        expect (pattern "*ABC*XYZ*".asString) toBe "(star Token)(ABC Token)(star Token)(XYZ Token)(star Token)"
+    }
+}
+describe "pattern matching behaviour" with {
+    specify "star matches anything" by {
+        expect (pattern "*".matches "abc") toBe true
+    }
+    specify "star matches nothing" by {
+        expect (pattern "*".matches "") toBe true
+    }
+    specify "star matches a single character" by {
+        expect (pattern "*".matches "3") toBe true
+    }
+}
+
+class pattern (patternChars:String) {
+    // returns a pattern object defined by patternChars
+    // In patternChars, * mathces any sequence of zero or more characters, 
+    // and any other chracters match themselves.
+    
+    def matchTokens = list.empty
+    var plainChars := ""
+    patternChars.do { ch → 
+        if (ch == "*") then {
+            if (plainChars.isEmpty.not) then { 
+                matchTokens.add(plainToken(plainChars))
+                plainChars := ""
+            }
+            matchTokens.add(starToken)
+        } else { 
+            plainChars := plainChars ++ ch
+        }
+    }
+    
+    method matches (aString:String) {
+        tokens (matchTokens) matches (aString) segment 1 to (aString.size)
+    }
+    
+    method tokens (toks) matches (aString) segment (start) to (end) is confidential {
+        if (toks.first).
+    }
+    
+    method asString { 
+        matchTokens.fold { sum, each → sum ++ each.asString } startingWith ""
+    }
+        
+}
+
+class starToken {
+    method matches (another) { true }
+    method asString { "(star Token)" }
+}
+
+class plainToken(tokenChars) {
+    method matches (another) { another.startsWith(tokenChars) }
+    method asString { "({tokenChars} Token)" }
+}
+