Added helper functions.

functions/alias.zsh

@@ -2,7 +2,7 @@ setopt correct        # Correct commands.
 setopt correct_all    # Correct all arguments.
 
 # The 'ls' Family
-if [[ "$DISABLE_COLOR" != 'true' ]]; then
+if ! check-bool "$DISABLE_COLOR"; then
   if [[ -f "$HOME/.dir_colors" ]] && ( (( $+commands[dircolors] )) || ( (( $+plugins[(er)gnu-utils] )) && (( $+commands[gdircolors] )) ) ); then
     eval $("${commands[dircolors]:-$commands[gdircolors]}" "$HOME/.dir_colors")
     alias ls='ls -hF --group-directories-first --color=auto'
@@ -80,7 +80,7 @@ else
 fi
 
 # Diff/Make
-if [[ "$DISABLE_COLOR" != 'true' ]]; then
+if ! check-bool "$DISABLE_COLOR"; then
   if (( $+commands[colordiff] )); then
     alias diff='colordiff -u'
     compdef colordiff=diff

functions/environment.zsh

@@ -64,7 +64,7 @@ export VISUAL="vim"
 export PAGER='less'
 
 # Grep
-if [[ "$DISABLE_COLOR" != 'true' ]]; then
+if ! check-bool "$DISABLE_COLOR"; then
   export GREP_COLOR='37;45'
   export GREP_OPTIONS='--color=auto'
 fi
@@ -89,7 +89,7 @@ if (( $+commands[lesspipe.sh] )); then
 fi
 
 # Termcap
-if [[ "$DISABLE_COLOR" != 'true' ]]; then
+if ! check-bool "$DISABLE_COLOR"; then
   export LESS_TERMCAP_mb=$'\E[01;31m'      # begin blinking
   export LESS_TERMCAP_md=$'\E[01;31m'      # begin bold
   export LESS_TERMCAP_me=$'\E[0m'          # end mode

functions/helper.zsh

@@ -0,0 +1,50 @@
+# Checks if a file can be autoloaded by trying to load it in a subshell.
+function autoloadable() {
+  ( unfunction $1 ; autoload -U +X $1 ) &> /dev/null
+}
+
+# Checks boolean variable for "true" (case insensitive "1", "y", "yes", "t", "true", "o", and "on").
+function check-bool {
+  [[ -n "$1" && "$1" == (1|[Yy]([Ee][Ss]|)|[Tt]([Rr][Uu][Ee]|)|[Oo]([Nn]|)) ]]
+}
+
+# Trap signals were generated with 'kill -l'.
+# DEBUG, EXIT, and ZERR are ZSH signals.
+TRAP_SIGNALS=(
+  ABRT ALRM BUS CHLD CONT EMT FPE HUP ILL INFO INT IO KILL PIPE PROF QUIT
+  SEGV STOP SYS TERM TRAP TSTP TTIN TTOU URG USR1 USR2 VTALRM WINCH XCPU XFSZ
+  DEBUG EXIT ZERR
+)
+
+# Adds a function to a list to be called when a trap is triggered.
+function add-zsh-trap {
+  if (( $# < 2 )); then
+    echo "Usage: $0 type function"
+    return 1
+  fi
+
+  if [[ -z "$TRAP_SIGNALS[(r)$1]" ]]; then
+    echo "$0: unknown signal: $1"
+    return 1
+  fi
+
+  local trap_functions="TRAP${1}_FUNCTIONS"
+  if (( ! ${(P)+trap_functions} )); then
+    typeset -gaU "$trap_functions"
+  fi
+  eval "$trap_functions+="$2""
+
+  if (( ! $+functions[TRAP${1}] )); then
+    eval "
+     function TRAP${1}() {
+        for trap_function in \"\$TRAP${1}_FUNCTIONS[@]\"; do
+          if (( \$+functions[\$trap_function] )); then
+            \"\$trap_function\" \"\$1\"
+          fi
+        done
+        return \$(( 128 + \$1 ))
+     }
+    "
+  fi
+}
+

functions/terminal.zsh

@@ -14,7 +14,7 @@ fi
 # Partially supports Mac OS X Terminal since it can't set window and tab separately.
 # Usage: title "tab title" "window title"
 function terminal-title {
-  if [[ "$DISABLE_AUTO_TITLE" != 'true' ]]; then
+  if ! check-bool "$DISABLE_AUTO_TITLE"; then
     if [[ "$TERM" == screen* ]]; then
       # Set GNU Screen's hardstatus (usually truncated at 20 characters).
       printf "\ek%s\e\\" ${(V)1}