diff --git a/src/formatter/parser.rs b/src/formatter/parser.rs
index 95c267a3a..3097cbabe 100644
--- a/src/formatter/parser.rs
+++ b/src/formatter/parser.rs
@@ -22,55 +22,45 @@ fn _parse_variable(variable: Pair<Rule>) -> &str {
 }
 
 fn _parse_text(text: Pair<Rule>) -> String {
-    let mut result = String::new();
-    for pair in text.into_inner() {
-        result.push_str(pair.as_str());
-    }
-    result
+    text.into_inner()
+        .map(|pair| pair.as_str().chars())
+        .flatten()
+        .collect()
 }
 
 fn _parse_format(format: Pair<Rule>) -> Vec<FormatElement> {
-    let mut result: Vec<FormatElement> = Vec::new();
-
-    for pair in format.into_inner() {
-        match pair.as_rule() {
-            Rule::text => result.push(FormatElement::Text(_parse_text(pair).into())),
-            Rule::variable => result.push(FormatElement::Variable(_parse_variable(pair).into())),
-            Rule::textgroup => result.push(FormatElement::TextGroup(_parse_textgroup(pair))),
+    format
+        .into_inner()
+        .map(|pair| match pair.as_rule() {
+            Rule::text => FormatElement::Text(_parse_text(pair).into()),
+            Rule::variable => FormatElement::Variable(_parse_variable(pair).into()),
+            Rule::textgroup => FormatElement::TextGroup(_parse_textgroup(pair)),
             _ => unreachable!(),
-        }
-    }
-
-    result
+        })
+        .collect()
 }
 
 fn _parse_style(style: Pair<Rule>) -> Vec<StyleElement> {
-    let mut result: Vec<StyleElement> = Vec::new();
-
-    for pair in style.into_inner() {
-        match pair.as_rule() {
-            Rule::text => result.push(StyleElement::Text(_parse_text(pair).into())),
-            Rule::variable => result.push(StyleElement::Variable(_parse_variable(pair).into())),
+    style
+        .into_inner()
+        .map(|pair| match pair.as_rule() {
+            Rule::string => StyleElement::Text(pair.as_str().into()),
+            Rule::variable => StyleElement::Variable(_parse_variable(pair).into()),
             _ => unreachable!(),
-        }
-    }
-
-    result
+        })
+        .collect()
 }
 
 pub fn parse(format: &str) -> Result<Vec<FormatElement>, Error<Rule>> {
-    let pairs = IdentParser::parse(Rule::expression, format)?;
-    let mut result: Vec<FormatElement> = Vec::new();
-
-    // Lifetime of Segment is the same as result
-    for pair in pairs.take_while(|pair| pair.as_rule() != Rule::EOI) {
-        match pair.as_rule() {
-            Rule::text => result.push(FormatElement::Text(_parse_text(pair).into())),
-            Rule::variable => result.push(FormatElement::Variable(_parse_variable(pair).into())),
-            Rule::textgroup => result.push(FormatElement::TextGroup(_parse_textgroup(pair))),
-            _ => unreachable!(),
-        }
-    }
-
-    Ok(result)
+    IdentParser::parse(Rule::expression, format).map(|pairs| {
+        pairs
+            .take_while(|pair| pair.as_rule() != Rule::EOI)
+            .map(|pair| match pair.as_rule() {
+                Rule::text => FormatElement::Text(_parse_text(pair).into()),
+                Rule::variable => FormatElement::Variable(_parse_variable(pair).into()),
+                Rule::textgroup => FormatElement::TextGroup(_parse_textgroup(pair)),
+                _ => unreachable!(),
+            })
+            .collect()
+    })
 }
diff --git a/src/formatter/spec.pest b/src/formatter/spec.pest
index 36be53be5..94d0b110b 100644
--- a/src/formatter/spec.pest
+++ b/src/formatter/spec.pest
@@ -1,16 +1,46 @@
+// Expression
+//
+// The expression of the format string.
+//
+// Should be started with SOI and ended with EOI, with a format string in it.
 expression = _{ SOI ~ value* ~ EOI }
 value = _{ text | variable | textgroup }
 
-variable = { "$" ~ variable_name }
-variable_name = @{ char+ }
+// Variable
+//
+// A variable is defined as one of the following:
+//
+// - A valid variable name followed by a `$` character (`$[a-zA-Z_][a-zA-Z0-9_]*`),
+//   e.g. `$variable`.
+//
+// - Some texts wrapped in a curly bracket (`${[^\(\)\[\]\\\${}]+}`),
+//   e.g. `${env:HOST}`.
+variable = { "$" ~ (variable_name | variable_scope) }
+variable_name = @{ ('a'..'z' | 'A'..'Z' | "_") ~ char* }
 char = _{ 'a'..'z' | 'A'..'Z' | '0'..'9' | "_" }
 
-text = { text_inner+ }
-text_inner = _{ text_inner_char | escape }
-text_inner_char = { !("[" | "]" | "(" | ")" | "$" | "\\") ~ ANY }
+variable_scope = _{ "{" ~ variable_scoped_name ~ "}" }
+variable_scoped_name = { scoped_char+ }
+scoped_char = _{ !(escaped_char | "{" | "}") ~ ANY }
+
+// Text
+//
+// Texts can be one of `string` or `escaped_char`, where string is one or more of
+// unescapable chars.
+//
+// This is implemented so as to ensure all functional characters are escaped.
+text = { (string | escape)+ }
+string = @{ text_inner_char+ }
+text_inner_char = { !escaped_char ~ ANY }
 escape = _{ "\\" ~ escaped_char }
 escaped_char = { "[" | "]" | "(" | ")" | "\\" | "$" }
 
+// TextGroup
+// 
+// A textgroup is a pair of `format` and `style` (`[format](style)`)
+//
+// - `format`: A format string, can contain any number of variables, texts or textgroups.
+// - `style`: A style string, can contain any number of variables or texts.
 textgroup = { "[" ~ format ~ "]" ~ "(" ~ style ~ ")" }
-format = { (variable | text | textgroup)* }
-style = { (variable | text)* }
+format = { value* }
+style = { (variable | string)* }
diff --git a/src/formatter/string_formatter.rs b/src/formatter/string_formatter.rs
index 8f33ce9ef..62843f156 100644
--- a/src/formatter/string_formatter.rs
+++ b/src/formatter/string_formatter.rs
@@ -86,15 +86,13 @@ impl<'a> StringFormatter<'a> {
         }
 
         fn _parse_format<'a>(
-            mut format: Vec<FormatElement<'a>>,
+            format: Vec<FormatElement<'a>>,
             style: Option<Style>,
             variables: &'a VariableMapType,
         ) -> Vec<Segment> {
-            let mut result: Vec<Segment> = Vec::new();
-
-            format.reverse();
-            while let Some(el) = format.pop() {
-                let mut segments = match el {
+            format
+                .into_iter()
+                .flat_map(|el| match el {
                     FormatElement::Text(text) => {
                         vec![_new_segment("_text".into(), text.into_owned(), style)]
                     }
@@ -127,11 +125,8 @@ impl<'a> StringFormatter<'a> {
                             }
                         })
                         .unwrap_or_default(),
-                };
-                result.append(&mut segments);
-            }
-
-            result
+                })
+                .collect()
         }
 
         _parse_format(self.format, default_style, &self.variables)
@@ -241,6 +236,18 @@ mod tests {
         match_next!(result_iter, "text1", None);
     }
 
+    #[test]
+    fn test_scoped_variable() {
+        const FORMAT_STR: &str = "${env:PWD}";
+
+        let formatter = StringFormatter::new(FORMAT_STR)
+            .unwrap()
+            .map(|variable| Some(format!("${{{}}}", variable)));
+        let result = formatter.parse(None);
+        let mut result_iter = result.iter();
+        match_next!(result_iter, "${env:PWD}", None);
+    }
+
     #[test]
     fn test_escaped_chars() {
         const FORMAT_STR: &str = r#"\\\[\$text\]\(red bold\)"#;