Data commit

Task/Substring/Tcl/substring-1.tcl

@@ -0,0 +1,16 @@
+set str "abcdefgh"
+set n 2
+set m 3
+
+puts [string range $str $n [expr {$n+$m-1}]]
+puts [string range $str $n end]
+puts [string range $str 0 end-1]
+# Because Tcl does substrings with a pair of indices, it is easier to express
+# the last two parts of the task as a chained pair of [string range] operations.
+# A maximally efficient solution would calculate the indices in full first.
+puts [string range [string range $str [string first "d" $str] end] [expr {$m-1}]]
+puts [string range [string range $str [string first "de" $str] end] [expr {$m-1}]]
+
+# From Tcl 8.5 onwards, these can be contracted somewhat.
+puts [string range [string range $str [string first "d" $str] end] $m-1]
+puts [string range [string range $str [string first "de" $str] end] $m-1]

Task/Substring/Tcl/substring-2.tcl

@@ -0,0 +1,19 @@
+# Define the substring operation, efficiently
+proc ::substring {string start length} {
+    string range $string $start [expr {$start + $length - 1}]
+}
+# Plumb it into the language
+set ops [namespace ensemble configure string -map]
+dict set ops substr ::substring
+namespace ensemble configure string -map $ops
+
+# Now show off by repeating the challenge!
+set str "abcdefgh"
+set n 2
+set m 3
+
+puts [string substr $str $n $m]
+puts [string range $str $n end]
+puts [string range $str 0 end-1]
+puts [string substr $str [string first "d" $str] $m]
+puts [string substr $str [string first "de" $str] $m]