String functions.

expreduce/builtin_string.go

@@ -44,5 +44,48 @@ func GetStringDefinitions() (defs []Definition) {
 		Name:     "Infix",
 		toString: (*Expression).ToStringInfix,
 	})
+	defs = append(defs, Definition{
+		Name: "StringLength",
+		legacyEvalFn: func(this *Expression, es *EvalState) Ex {
+			if len(this.Parts) != 2 {
+				return this
+			}
+			asStr, isStr := this.Parts[1].(*String)
+			if !isStr {
+				return this
+			}
+			return NewInt(int64(len(asStr.Val)))
+		},
+	})
+	defs = append(defs, Definition{
+		Name: "StringTake",
+		legacyEvalFn: func(this *Expression, es *EvalState) Ex {
+			if len(this.Parts) != 3 {
+				return this
+			}
+			asStr, isStr := this.Parts[1].(*String)
+			if !isStr {
+				return this
+			}
+			asList, isList := HeadAssertion(this.Parts[2], "System`List")
+			if !isList || len(asList.Parts) != 3 {
+				return this
+			}
+			sInt, sIsInt := asList.Parts[1].(*Integer)
+			eInt, eIsInt := asList.Parts[2].(*Integer)
+			if !sIsInt || !eIsInt {
+				return this
+			}
+			s := int(sInt.Val.Int64()-1)
+			e := int(eInt.Val.Int64()-1)
+			if s < 0 || e >= len(asStr.Val) {
+				return this
+			}
+			if e < s {
+				return &String{""}
+			}
+			return &String{asStr.Val[s:e+1]}
+		},
+	})
 	return
 }

expreduce/resources/string.m

@@ -37,3 +37,23 @@
         ESameTest["(bar|fuzz|zip)", Infix[foo[Global`bar, Global`fuzz, Global`zip], "|"] // ToString]
     ]
 };
+
+StringLength::usage = "`StringLength[s]` returns the length of s.";
+Attributes[StringLength] = {Listable, Protected};
+Tests`StringLength = {
+    ESimpleExamples[
+        ESameTest[5, StringLength["Hello"]]
+    ]
+};
+
+StringTake::usage = "`StringTake[s, {start, end}]` takes a substring of s.";
+Attributes[StringTake] = {Protected};
+Tests`StringTake = {
+    ESimpleExamples[
+        ESameTest["h", StringTake["hello", {1, 1}]],
+        ESameTest[StringTake["hello", {0, 1}], StringTake["hello", {0, 1}]],
+        ESameTest["hello", StringTake["hello", {1, StringLength["hello"]}]],
+        ESameTest["", StringTake["hello", {2, 1}]],
+        ESameTest[StringTake["hello", {2, 999}], StringTake["hello", {2, 999}]]
+    ]
+};