diff --git a/src/libexpr/lexer.l b/src/libexpr/lexer.l
index 9addb3ae8..cfd61c90e 100644
--- a/src/libexpr/lexer.l
+++ b/src/libexpr/lexer.l
@@ -29,12 +29,7 @@ using namespace nix;
 
 namespace nix {
 
-static inline PosIdx makeCurPos(const YYLTYPE & loc, ParseData * data)
-{
-    return data->state.positions.add(data->origin, loc.first_line, loc.first_column);
-}
-
-#define CUR_POS makeCurPos(*yylloc, data)
+#define CUR_POS state->makeCurPos(*yylloc)
 
 static void initLoc(YYLTYPE * loc)
 {
@@ -153,7 +148,7 @@ or          { return OR_KW; }
               } catch (const boost::bad_lexical_cast &) {
                   throw ParseError({
                       .msg = hintfmt("invalid integer '%1%'", yytext),
-                      .errPos = data->state.positions[CUR_POS],
+                      .errPos = state->state.positions[CUR_POS],
                   });
               }
               return INT_LIT;
@@ -163,7 +158,7 @@ or          { return OR_KW; }
               if (errno != 0)
                   throw ParseError({
                       .msg = hintfmt("invalid float '%1%'", yytext),
-                      .errPos = data->state.positions[CUR_POS],
+                      .errPos = state->state.positions[CUR_POS],
                   });
               return FLOAT_LIT;
             }
@@ -186,7 +181,7 @@ or          { return OR_KW; }
                 /* It is impossible to match strings ending with '$' with one
                    regex because trailing contexts are only valid at the end
                    of a rule. (A sane but undocumented limitation.) */
-                yylval->str = unescapeStr(data->symbols, yytext, yyleng);
+                yylval->str = unescapeStr(state->symbols, yytext, yyleng);
                 return STR;
               }
 <STRING>\$\{  { PUSH_STATE(DEFAULT); return DOLLAR_CURLY; }
@@ -214,7 +209,7 @@ or          { return OR_KW; }
                    return IND_STR;
                  }
 <IND_STRING>\'\'\\{ANY} {
-                   yylval->str = unescapeStr(data->symbols, yytext + 2, yyleng - 2);
+                   yylval->str = unescapeStr(state->symbols, yytext + 2, yyleng - 2);
                    return IND_STR;
                  }
 <IND_STRING>\$\{ { PUSH_STATE(DEFAULT); return DOLLAR_CURLY; }
@@ -292,7 +287,7 @@ or          { return OR_KW; }
 <INPATH_SLASH><<EOF>> {
   throw ParseError({
       .msg = hintfmt("path has a trailing slash"),
-      .errPos = data->state.positions[CUR_POS],
+      .errPos = state->state.positions[CUR_POS],
   });
 }
 
diff --git a/src/libexpr/parser-state.hh b/src/libexpr/parser-state.hh
new file mode 100644
index 000000000..b33311743
--- /dev/null
+++ b/src/libexpr/parser-state.hh
@@ -0,0 +1,262 @@
+#pragma once
+
+#include "eval.hh"
+
+namespace nix {
+
+// using C a struct allows us to avoid having to define the special
+// members that using string_view here would implicitly delete.
+struct StringToken {
+  const char * p;
+  size_t l;
+  bool hasIndentation;
+  operator std::string_view() const { return {p, l}; }
+};
+
+struct ParserLocation {
+    int first_line, first_column;
+    int last_line, last_column;
+
+    // backup to recover from yyless(0)
+    int stashed_first_line, stashed_first_column;
+    int stashed_last_line, stashed_last_column;
+
+    void stash() {
+        stashed_first_line = first_line;
+        stashed_first_column = first_column;
+        stashed_last_line = last_line;
+        stashed_last_column = last_column;
+    }
+
+    void unstash() {
+        first_line = stashed_first_line;
+        first_column = stashed_first_column;
+        last_line = stashed_last_line;
+        last_column = stashed_last_column;
+    }
+};
+
+struct ParserState {
+    EvalState & state;
+    SymbolTable & symbols;
+    Expr * result;
+    SourcePath basePath;
+    PosTable::Origin origin;
+
+    void dupAttr(const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos);
+    void dupAttr(Symbol attr, const PosIdx pos, const PosIdx prevPos);
+    void addAttr(ExprAttrs * attrs, AttrPath && attrPath, Expr * e, const PosIdx pos);
+    Formals * validateFormals(Formals * formals, PosIdx pos = noPos, Symbol arg = {});
+    Expr * stripIndentation(const PosIdx pos,
+        std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>> && es);
+    PosIdx makeCurPos(const ParserLocation & loc);
+};
+
+inline void ParserState::dupAttr(const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos)
+{
+    throw ParseError({
+         .msg = hintfmt("attribute '%1%' already defined at %2%",
+             showAttrPath(state.symbols, attrPath), state.positions[prevPos]),
+         .errPos = state.positions[pos]
+    });
+}
+
+inline void ParserState::dupAttr(Symbol attr, const PosIdx pos, const PosIdx prevPos)
+{
+    throw ParseError({
+        .msg = hintfmt("attribute '%1%' already defined at %2%", state.symbols[attr], state.positions[prevPos]),
+        .errPos = state.positions[pos]
+    });
+}
+
+inline void ParserState::addAttr(ExprAttrs * attrs, AttrPath && attrPath, Expr * e, const PosIdx pos)
+{
+    AttrPath::iterator i;
+    // All attrpaths have at least one attr
+    assert(!attrPath.empty());
+    // Checking attrPath validity.
+    // ===========================
+    for (i = attrPath.begin(); i + 1 < attrPath.end(); i++) {
+        if (i->symbol) {
+            ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
+            if (j != attrs->attrs.end()) {
+                if (!j->second.inherited) {
+                    ExprAttrs * attrs2 = dynamic_cast<ExprAttrs *>(j->second.e);
+                    if (!attrs2) dupAttr(attrPath, pos, j->second.pos);
+                    attrs = attrs2;
+                } else
+                    dupAttr(attrPath, pos, j->second.pos);
+            } else {
+                ExprAttrs * nested = new ExprAttrs;
+                attrs->attrs[i->symbol] = ExprAttrs::AttrDef(nested, pos);
+                attrs = nested;
+            }
+        } else {
+            ExprAttrs *nested = new ExprAttrs;
+            attrs->dynamicAttrs.push_back(ExprAttrs::DynamicAttrDef(i->expr, nested, pos));
+            attrs = nested;
+        }
+    }
+    // Expr insertion.
+    // ==========================
+    if (i->symbol) {
+        ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
+        if (j != attrs->attrs.end()) {
+            // This attr path is already defined. However, if both
+            // e and the expr pointed by the attr path are two attribute sets,
+            // we want to merge them.
+            // Otherwise, throw an error.
+            auto ae = dynamic_cast<ExprAttrs *>(e);
+            auto jAttrs = dynamic_cast<ExprAttrs *>(j->second.e);
+            if (jAttrs && ae) {
+                for (auto & ad : ae->attrs) {
+                    auto j2 = jAttrs->attrs.find(ad.first);
+                    if (j2 != jAttrs->attrs.end()) // Attr already defined in iAttrs, error.
+                        dupAttr(ad.first, j2->second.pos, ad.second.pos);
+                    jAttrs->attrs.emplace(ad.first, ad.second);
+                }
+                jAttrs->dynamicAttrs.insert(jAttrs->dynamicAttrs.end(), ae->dynamicAttrs.begin(), ae->dynamicAttrs.end());
+            } else {
+                dupAttr(attrPath, pos, j->second.pos);
+            }
+        } else {
+            // This attr path is not defined. Let's create it.
+            attrs->attrs.emplace(i->symbol, ExprAttrs::AttrDef(e, pos));
+            e->setName(i->symbol);
+        }
+    } else {
+        attrs->dynamicAttrs.push_back(ExprAttrs::DynamicAttrDef(i->expr, e, pos));
+    }
+}
+
+inline Formals * ParserState::validateFormals(Formals * formals, PosIdx pos, Symbol arg)
+{
+    std::sort(formals->formals.begin(), formals->formals.end(),
+        [] (const auto & a, const auto & b) {
+            return std::tie(a.name, a.pos) < std::tie(b.name, b.pos);
+        });
+
+    std::optional<std::pair<Symbol, PosIdx>> duplicate;
+    for (size_t i = 0; i + 1 < formals->formals.size(); i++) {
+        if (formals->formals[i].name != formals->formals[i + 1].name)
+            continue;
+        std::pair thisDup{formals->formals[i].name, formals->formals[i + 1].pos};
+        duplicate = std::min(thisDup, duplicate.value_or(thisDup));
+    }
+    if (duplicate)
+        throw ParseError({
+            .msg = hintfmt("duplicate formal function argument '%1%'", symbols[duplicate->first]),
+            .errPos = state.positions[duplicate->second]
+        });
+
+    if (arg && formals->has(arg))
+        throw ParseError({
+            .msg = hintfmt("duplicate formal function argument '%1%'", symbols[arg]),
+            .errPos = state.positions[pos]
+        });
+
+    return formals;
+}
+
+inline Expr * ParserState::stripIndentation(const PosIdx pos,
+    std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>> && es)
+{
+    if (es.empty()) return new ExprString("");
+
+    /* Figure out the minimum indentation.  Note that by design
+       whitespace-only final lines are not taken into account.  (So
+       the " " in "\n ''" is ignored, but the " " in "\n foo''" is.) */
+    bool atStartOfLine = true; /* = seen only whitespace in the current line */
+    size_t minIndent = 1000000;
+    size_t curIndent = 0;
+    for (auto & [i_pos, i] : es) {
+        auto * str = std::get_if<StringToken>(&i);
+        if (!str || !str->hasIndentation) {
+            /* Anti-quotations and escaped characters end the current start-of-line whitespace. */
+            if (atStartOfLine) {
+                atStartOfLine = false;
+                if (curIndent < minIndent) minIndent = curIndent;
+            }
+            continue;
+        }
+        for (size_t j = 0; j < str->l; ++j) {
+            if (atStartOfLine) {
+                if (str->p[j] == ' ')
+                    curIndent++;
+                else if (str->p[j] == '\n') {
+                    /* Empty line, doesn't influence minimum
+                       indentation. */
+                    curIndent = 0;
+                } else {
+                    atStartOfLine = false;
+                    if (curIndent < minIndent) minIndent = curIndent;
+                }
+            } else if (str->p[j] == '\n') {
+                atStartOfLine = true;
+                curIndent = 0;
+            }
+        }
+    }
+
+    /* Strip spaces from each line. */
+    auto * es2 = new std::vector<std::pair<PosIdx, Expr *>>;
+    atStartOfLine = true;
+    size_t curDropped = 0;
+    size_t n = es.size();
+    auto i = es.begin();
+    const auto trimExpr = [&] (Expr * e) {
+        atStartOfLine = false;
+        curDropped = 0;
+        es2->emplace_back(i->first, e);
+    };
+    const auto trimString = [&] (const StringToken & t) {
+        std::string s2;
+        for (size_t j = 0; j < t.l; ++j) {
+            if (atStartOfLine) {
+                if (t.p[j] == ' ') {
+                    if (curDropped++ >= minIndent)
+                        s2 += t.p[j];
+                }
+                else if (t.p[j] == '\n') {
+                    curDropped = 0;
+                    s2 += t.p[j];
+                } else {
+                    atStartOfLine = false;
+                    curDropped = 0;
+                    s2 += t.p[j];
+                }
+            } else {
+                s2 += t.p[j];
+                if (t.p[j] == '\n') atStartOfLine = true;
+            }
+        }
+
+        /* Remove the last line if it is empty and consists only of
+           spaces. */
+        if (n == 1) {
+            std::string::size_type p = s2.find_last_of('\n');
+            if (p != std::string::npos && s2.find_first_not_of(' ', p + 1) == std::string::npos)
+                s2 = std::string(s2, 0, p + 1);
+        }
+
+        es2->emplace_back(i->first, new ExprString(std::move(s2)));
+    };
+    for (; i != es.end(); ++i, --n) {
+        std::visit(overloaded { trimExpr, trimString }, i->second);
+    }
+
+    /* If this is a single string, then don't do a concatenation. */
+    if (es2->size() == 1 && dynamic_cast<ExprString *>((*es2)[0].second)) {
+        auto *const result = (*es2)[0].second;
+        delete es2;
+        return result;
+    }
+    return new ExprConcatStrings(pos, true, es2);
+}
+
+inline PosIdx ParserState::makeCurPos(const ParserLocation & loc)
+{
+    return state.positions.add(origin, loc.first_line, loc.first_column);
+}
+
+}
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index beb660e36..7ce493df5 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -5,9 +5,9 @@
 %defines
 /* %no-lines */
 %parse-param { void * scanner }
-%parse-param { nix::ParseData * data }
+%parse-param { nix::ParserState * state }
 %lex-param { void * scanner }
-%lex-param { nix::ParseData * data }
+%lex-param { nix::ParserState * state }
 %expect 1
 %expect-rr 1
 
@@ -26,64 +26,11 @@
 #include "eval.hh"
 #include "eval-settings.hh"
 #include "globals.hh"
-
-// using C a struct allows us to avoid having to define the special
-// members that using string_view here would implicitly delete.
-struct StringToken {
-  const char * p;
-  size_t l;
-  bool hasIndentation;
-  operator std::string_view() const { return {p, l}; }
-};
-
-namespace nix {
+#include "parser-state.hh"
 
 #define YYLTYPE ::nix::ParserLocation
-    struct ParserLocation
-    {
-        int first_line, first_column;
-        int last_line, last_column;
-
-        // backup to recover from yyless(0)
-        int stashed_first_line, stashed_first_column;
-        int stashed_last_line, stashed_last_column;
-
-        void stash() {
-          stashed_first_line = first_line;
-          stashed_first_column = first_column;
-          stashed_last_line = last_line;
-          stashed_last_column = last_column;
-        }
-
-        void unstash() {
-          first_line = stashed_first_line;
-          first_column = stashed_first_column;
-          last_line = stashed_last_line;
-          last_column = stashed_last_column;
-        }
-    };
-
-    struct ParseData
-    {
-        EvalState & state;
-        SymbolTable & symbols;
-        Expr * result;
-        SourcePath basePath;
-        PosTable::Origin origin;
-
-        void dupAttr(const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos);
-        void dupAttr(Symbol attr, const PosIdx pos, const PosIdx prevPos);
-        void addAttr(ExprAttrs * attrs, AttrPath && attrPath, Expr * e, const PosIdx pos);
-        Formals * validateFormals(Formals * formals, PosIdx pos = noPos, Symbol arg = {});
-        Expr * stripIndentation(const PosIdx pos,
-            std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>> && es);
-        PosIdx makeCurPos(const ParserLocation & loc);
-    };
-
-}
-
 #define YY_DECL int yylex \
-    (YYSTYPE * yylval_param, YYLTYPE * yylloc_param, yyscan_t yyscanner, nix::ParseData * data)
+    (YYSTYPE * yylval_param, YYLTYPE * yylloc_param, yyscan_t yyscanner, nix::ParserState * state)
 
 #endif
 
@@ -98,232 +45,14 @@ YY_DECL;
 
 using namespace nix;
 
-
-namespace nix {
+#define CUR_POS state->makeCurPos(*yylocp)
 
 
-void ParseData::dupAttr(const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos)
-{
-    throw ParseError({
-         .msg = hintfmt("attribute '%1%' already defined at %2%",
-             showAttrPath(state.symbols, attrPath), state.positions[prevPos]),
-         .errPos = state.positions[pos]
-    });
-}
-
-void ParseData::dupAttr(Symbol attr, const PosIdx pos, const PosIdx prevPos)
-{
-    throw ParseError({
-        .msg = hintfmt("attribute '%1%' already defined at %2%", state.symbols[attr], state.positions[prevPos]),
-        .errPos = state.positions[pos]
-    });
-}
-
-
-void ParseData::addAttr(ExprAttrs * attrs, AttrPath && attrPath, Expr * e, const PosIdx pos)
-{
-    AttrPath::iterator i;
-    // All attrpaths have at least one attr
-    assert(!attrPath.empty());
-    // Checking attrPath validity.
-    // ===========================
-    for (i = attrPath.begin(); i + 1 < attrPath.end(); i++) {
-        if (i->symbol) {
-            ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
-            if (j != attrs->attrs.end()) {
-                if (!j->second.inherited) {
-                    ExprAttrs * attrs2 = dynamic_cast<ExprAttrs *>(j->second.e);
-                    if (!attrs2) dupAttr(attrPath, pos, j->second.pos);
-                    attrs = attrs2;
-                } else
-                    dupAttr(attrPath, pos, j->second.pos);
-            } else {
-                ExprAttrs * nested = new ExprAttrs;
-                attrs->attrs[i->symbol] = ExprAttrs::AttrDef(nested, pos);
-                attrs = nested;
-            }
-        } else {
-            ExprAttrs *nested = new ExprAttrs;
-            attrs->dynamicAttrs.push_back(ExprAttrs::DynamicAttrDef(i->expr, nested, pos));
-            attrs = nested;
-        }
-    }
-    // Expr insertion.
-    // ==========================
-    if (i->symbol) {
-        ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
-        if (j != attrs->attrs.end()) {
-            // This attr path is already defined. However, if both
-            // e and the expr pointed by the attr path are two attribute sets,
-            // we want to merge them.
-            // Otherwise, throw an error.
-            auto ae = dynamic_cast<ExprAttrs *>(e);
-            auto jAttrs = dynamic_cast<ExprAttrs *>(j->second.e);
-            if (jAttrs && ae) {
-                for (auto & ad : ae->attrs) {
-                    auto j2 = jAttrs->attrs.find(ad.first);
-                    if (j2 != jAttrs->attrs.end()) // Attr already defined in iAttrs, error.
-                        dupAttr(ad.first, j2->second.pos, ad.second.pos);
-                    jAttrs->attrs.emplace(ad.first, ad.second);
-                }
-                jAttrs->dynamicAttrs.insert(jAttrs->dynamicAttrs.end(), ae->dynamicAttrs.begin(), ae->dynamicAttrs.end());
-            } else {
-                dupAttr(attrPath, pos, j->second.pos);
-            }
-        } else {
-            // This attr path is not defined. Let's create it.
-            attrs->attrs.emplace(i->symbol, ExprAttrs::AttrDef(e, pos));
-            e->setName(i->symbol);
-        }
-    } else {
-        attrs->dynamicAttrs.push_back(ExprAttrs::DynamicAttrDef(i->expr, e, pos));
-    }
-}
-
-
-Formals * ParseData::validateFormals(Formals * formals, PosIdx pos, Symbol arg)
-{
-    std::sort(formals->formals.begin(), formals->formals.end(),
-        [] (const auto & a, const auto & b) {
-            return std::tie(a.name, a.pos) < std::tie(b.name, b.pos);
-        });
-
-    std::optional<std::pair<Symbol, PosIdx>> duplicate;
-    for (size_t i = 0; i + 1 < formals->formals.size(); i++) {
-        if (formals->formals[i].name != formals->formals[i + 1].name)
-            continue;
-        std::pair thisDup{formals->formals[i].name, formals->formals[i + 1].pos};
-        duplicate = std::min(thisDup, duplicate.value_or(thisDup));
-    }
-    if (duplicate)
-        throw ParseError({
-            .msg = hintfmt("duplicate formal function argument '%1%'", symbols[duplicate->first]),
-            .errPos = state.positions[duplicate->second]
-        });
-
-    if (arg && formals->has(arg))
-        throw ParseError({
-            .msg = hintfmt("duplicate formal function argument '%1%'", symbols[arg]),
-            .errPos = state.positions[pos]
-        });
-
-    return formals;
-}
-
-
-Expr * ParseData::stripIndentation(const PosIdx pos,
-    std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>> && es)
-{
-    if (es.empty()) return new ExprString("");
-
-    /* Figure out the minimum indentation.  Note that by design
-       whitespace-only final lines are not taken into account.  (So
-       the " " in "\n ''" is ignored, but the " " in "\n foo''" is.) */
-    bool atStartOfLine = true; /* = seen only whitespace in the current line */
-    size_t minIndent = 1000000;
-    size_t curIndent = 0;
-    for (auto & [i_pos, i] : es) {
-        auto * str = std::get_if<StringToken>(&i);
-        if (!str || !str->hasIndentation) {
-            /* Anti-quotations and escaped characters end the current start-of-line whitespace. */
-            if (atStartOfLine) {
-                atStartOfLine = false;
-                if (curIndent < minIndent) minIndent = curIndent;
-            }
-            continue;
-        }
-        for (size_t j = 0; j < str->l; ++j) {
-            if (atStartOfLine) {
-                if (str->p[j] == ' ')
-                    curIndent++;
-                else if (str->p[j] == '\n') {
-                    /* Empty line, doesn't influence minimum
-                       indentation. */
-                    curIndent = 0;
-                } else {
-                    atStartOfLine = false;
-                    if (curIndent < minIndent) minIndent = curIndent;
-                }
-            } else if (str->p[j] == '\n') {
-                atStartOfLine = true;
-                curIndent = 0;
-            }
-        }
-    }
-
-    /* Strip spaces from each line. */
-    auto * es2 = new std::vector<std::pair<PosIdx, Expr *>>;
-    atStartOfLine = true;
-    size_t curDropped = 0;
-    size_t n = es.size();
-    auto i = es.begin();
-    const auto trimExpr = [&] (Expr * e) {
-        atStartOfLine = false;
-        curDropped = 0;
-        es2->emplace_back(i->first, e);
-    };
-    const auto trimString = [&] (const StringToken & t) {
-        std::string s2;
-        for (size_t j = 0; j < t.l; ++j) {
-            if (atStartOfLine) {
-                if (t.p[j] == ' ') {
-                    if (curDropped++ >= minIndent)
-                        s2 += t.p[j];
-                }
-                else if (t.p[j] == '\n') {
-                    curDropped = 0;
-                    s2 += t.p[j];
-                } else {
-                    atStartOfLine = false;
-                    curDropped = 0;
-                    s2 += t.p[j];
-                }
-            } else {
-                s2 += t.p[j];
-                if (t.p[j] == '\n') atStartOfLine = true;
-            }
-        }
-
-        /* Remove the last line if it is empty and consists only of
-           spaces. */
-        if (n == 1) {
-            std::string::size_type p = s2.find_last_of('\n');
-            if (p != std::string::npos && s2.find_first_not_of(' ', p + 1) == std::string::npos)
-                s2 = std::string(s2, 0, p + 1);
-        }
-
-        es2->emplace_back(i->first, new ExprString(std::move(s2)));
-    };
-    for (; i != es.end(); ++i, --n) {
-        std::visit(overloaded { trimExpr, trimString }, i->second);
-    }
-
-    /* If this is a single string, then don't do a concatenation. */
-    if (es2->size() == 1 && dynamic_cast<ExprString *>((*es2)[0].second)) {
-        auto *const result = (*es2)[0].second;
-        delete es2;
-        return result;
-    }
-    return new ExprConcatStrings(pos, true, es2);
-}
-
-
-PosIdx ParseData::makeCurPos(const ParserLocation & loc)
-{
-    return state.positions.add(origin, loc.first_line, loc.first_column);
-}
-
-#define CUR_POS data->makeCurPos(*yylocp)
-
-
-}
-
-
-void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * error)
+void yyerror(YYLTYPE * loc, yyscan_t scanner, ParserState * state, const char * error)
 {
     throw ParseError({
         .msg = hintfmt(error),
-        .errPos = data->state.positions[data->makeCurPos(*loc)]
+        .errPos = state->state.positions[state->makeCurPos(*loc)]
     });
 }
 
@@ -339,13 +68,13 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
   nix::Formal * formal;
   nix::NixInt n;
   nix::NixFloat nf;
-  StringToken id; // !!! -> Symbol
-  StringToken path;
-  StringToken uri;
-  StringToken str;
+  nix::StringToken id; // !!! -> Symbol
+  nix::StringToken path;
+  nix::StringToken uri;
+  nix::StringToken str;
   std::vector<nix::AttrName> * attrNames;
   std::vector<std::pair<nix::PosIdx, nix::Expr *>> * string_parts;
-  std::vector<std::pair<nix::PosIdx, std::variant<nix::Expr *, StringToken>>> * ind_string_parts;
+  std::vector<std::pair<nix::PosIdx, std::variant<nix::Expr *, nix::StringToken>>> * ind_string_parts;
 }
 
 %type <e> start expr expr_function expr_if expr_op
@@ -385,24 +114,24 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
 
 %%
 
-start: expr { data->result = $1; };
+start: expr { state->result = $1; };
 
 expr: expr_function;
 
 expr_function
   : ID ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), 0, $3); }
+    { $$ = new ExprLambda(CUR_POS, state->symbols.create($1), 0, $3); }
   | '{' formals '}' ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->validateFormals($2), $5); }
+    { $$ = new ExprLambda(CUR_POS, state->validateFormals($2), $5); }
   | '{' formals '}' '@' ID ':' expr_function
     {
-      auto arg = data->symbols.create($5);
-      $$ = new ExprLambda(CUR_POS, arg, data->validateFormals($2, CUR_POS, arg), $7);
+      auto arg = state->symbols.create($5);
+      $$ = new ExprLambda(CUR_POS, arg, state->validateFormals($2, CUR_POS, arg), $7);
     }
   | ID '@' '{' formals '}' ':' expr_function
     {
-      auto arg = data->symbols.create($1);
-      $$ = new ExprLambda(CUR_POS, arg, data->validateFormals($4, CUR_POS, arg), $7);
+      auto arg = state->symbols.create($1);
+      $$ = new ExprLambda(CUR_POS, arg, state->validateFormals($4, CUR_POS, arg), $7);
     }
   | ASSERT expr ';' expr_function
     { $$ = new ExprAssert(CUR_POS, $2, $4); }
@@ -412,7 +141,7 @@ expr_function
     { if (!$2->dynamicAttrs.empty())
         throw ParseError({
             .msg = hintfmt("dynamic attributes not allowed in let"),
-            .errPos = data->state.positions[CUR_POS]
+            .errPos = state->state.positions[CUR_POS]
         });
       $$ = new ExprLet($2, $4);
     }
@@ -426,24 +155,24 @@ expr_if
 
 expr_op
   : '!' expr_op %prec NOT { $$ = new ExprOpNot($2); }
-  | '-' expr_op %prec NEGATE { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__sub")), {new ExprInt(0), $2}); }
+  | '-' expr_op %prec NEGATE { $$ = new ExprCall(CUR_POS, new ExprVar(state->symbols.create("__sub")), {new ExprInt(0), $2}); }
   | expr_op EQ expr_op { $$ = new ExprOpEq($1, $3); }
   | expr_op NEQ expr_op { $$ = new ExprOpNEq($1, $3); }
-  | expr_op '<' expr_op { $$ = new ExprCall(data->makeCurPos(@2), new ExprVar(data->symbols.create("__lessThan")), {$1, $3}); }
-  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprCall(data->makeCurPos(@2), new ExprVar(data->symbols.create("__lessThan")), {$3, $1})); }
-  | expr_op '>' expr_op { $$ = new ExprCall(data->makeCurPos(@2), new ExprVar(data->symbols.create("__lessThan")), {$3, $1}); }
-  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprCall(data->makeCurPos(@2), new ExprVar(data->symbols.create("__lessThan")), {$1, $3})); }
-  | expr_op AND expr_op { $$ = new ExprOpAnd(data->makeCurPos(@2), $1, $3); }
-  | expr_op OR expr_op { $$ = new ExprOpOr(data->makeCurPos(@2), $1, $3); }
-  | expr_op IMPL expr_op { $$ = new ExprOpImpl(data->makeCurPos(@2), $1, $3); }
-  | expr_op UPDATE expr_op { $$ = new ExprOpUpdate(data->makeCurPos(@2), $1, $3); }
+  | expr_op '<' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__lessThan")), {$1, $3}); }
+  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__lessThan")), {$3, $1})); }
+  | expr_op '>' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__lessThan")), {$3, $1}); }
+  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__lessThan")), {$1, $3})); }
+  | expr_op AND expr_op { $$ = new ExprOpAnd(state->makeCurPos(@2), $1, $3); }
+  | expr_op OR expr_op { $$ = new ExprOpOr(state->makeCurPos(@2), $1, $3); }
+  | expr_op IMPL expr_op { $$ = new ExprOpImpl(state->makeCurPos(@2), $1, $3); }
+  | expr_op UPDATE expr_op { $$ = new ExprOpUpdate(state->makeCurPos(@2), $1, $3); }
   | expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, std::move(*$3)); delete $3; }
   | expr_op '+' expr_op
-    { $$ = new ExprConcatStrings(data->makeCurPos(@2), false, new std::vector<std::pair<PosIdx, Expr *> >({{data->makeCurPos(@1), $1}, {data->makeCurPos(@3), $3}})); }
-  | expr_op '-' expr_op { $$ = new ExprCall(data->makeCurPos(@2), new ExprVar(data->symbols.create("__sub")), {$1, $3}); }
-  | expr_op '*' expr_op { $$ = new ExprCall(data->makeCurPos(@2), new ExprVar(data->symbols.create("__mul")), {$1, $3}); }
-  | expr_op '/' expr_op { $$ = new ExprCall(data->makeCurPos(@2), new ExprVar(data->symbols.create("__div")), {$1, $3}); }
-  | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists(data->makeCurPos(@2), $1, $3); }
+    { $$ = new ExprConcatStrings(state->makeCurPos(@2), false, new std::vector<std::pair<PosIdx, Expr *> >({{state->makeCurPos(@1), $1}, {state->makeCurPos(@3), $3}})); }
+  | expr_op '-' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__sub")), {$1, $3}); }
+  | expr_op '*' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__mul")), {$1, $3}); }
+  | expr_op '/' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__div")), {$1, $3}); }
+  | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists(state->makeCurPos(@2), $1, $3); }
   | expr_app
   ;
 
@@ -466,7 +195,7 @@ expr_select
   | /* Backwards compatibility: because Nixpkgs has a rarely used
        function named ‘or’, allow stuff like ‘map or [...]’. */
     expr_simple OR_KW
-    { $$ = new ExprCall(CUR_POS, $1, {new ExprVar(CUR_POS, data->symbols.create("or"))}); }
+    { $$ = new ExprCall(CUR_POS, $1, {new ExprVar(CUR_POS, state->symbols.create("or"))}); }
   | expr_simple
   ;
 
@@ -476,25 +205,25 @@ expr_simple
       if ($1.l == s.size() && strncmp($1.p, s.data(), s.size()) == 0)
           $$ = new ExprPos(CUR_POS);
       else
-          $$ = new ExprVar(CUR_POS, data->symbols.create($1));
+          $$ = new ExprVar(CUR_POS, state->symbols.create($1));
   }
   | INT_LIT { $$ = new ExprInt($1); }
   | FLOAT_LIT { $$ = new ExprFloat($1); }
   | '"' string_parts '"' { $$ = $2; }
   | IND_STRING_OPEN ind_string_parts IND_STRING_CLOSE {
-      $$ = data->stripIndentation(CUR_POS, std::move(*$2));
+      $$ = state->stripIndentation(CUR_POS, std::move(*$2));
       delete $2;
   }
   | path_start PATH_END
   | path_start string_parts_interpolated PATH_END {
-      $2->insert($2->begin(), {data->makeCurPos(@1), $1});
+      $2->insert($2->begin(), {state->makeCurPos(@1), $1});
       $$ = new ExprConcatStrings(CUR_POS, false, $2);
   }
   | SPATH {
       std::string path($1.p + 1, $1.l - 2);
       $$ = new ExprCall(CUR_POS,
-          new ExprVar(data->symbols.create("__findFile")),
-          {new ExprVar(data->symbols.create("__nixPath")),
+          new ExprVar(state->symbols.create("__findFile")),
+          {new ExprVar(state->symbols.create("__nixPath")),
            new ExprString(std::move(path))});
   }
   | URI {
@@ -502,7 +231,7 @@ expr_simple
       if (noURLLiterals)
           throw ParseError({
               .msg = hintfmt("URL literals are disabled"),
-              .errPos = data->state.positions[CUR_POS]
+              .errPos = state->state.positions[CUR_POS]
           });
       $$ = new ExprString(std::string($1));
   }
@@ -510,7 +239,7 @@ expr_simple
   /* Let expressions `let {..., body = ...}' are just desugared
      into `(rec {..., body = ...}).body'. */
   | LET '{' binds '}'
-    { $3->recursive = true; $$ = new ExprSelect(noPos, $3, data->symbols.create("body")); }
+    { $3->recursive = true; $$ = new ExprSelect(noPos, $3, state->symbols.create("body")); }
   | REC '{' binds '}'
     { $3->recursive = true; $$ = $3; }
   | '{' binds '}'
@@ -526,23 +255,23 @@ string_parts
 
 string_parts_interpolated
   : string_parts_interpolated STR
-  { $$ = $1; $1->emplace_back(data->makeCurPos(@2), new ExprString(std::string($2))); }
-  | string_parts_interpolated DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(data->makeCurPos(@2), $3); }
-  | DOLLAR_CURLY expr '}' { $$ = new std::vector<std::pair<PosIdx, Expr *>>; $$->emplace_back(data->makeCurPos(@1), $2); }
+  { $$ = $1; $1->emplace_back(state->makeCurPos(@2), new ExprString(std::string($2))); }
+  | string_parts_interpolated DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(state->makeCurPos(@2), $3); }
+  | DOLLAR_CURLY expr '}' { $$ = new std::vector<std::pair<PosIdx, Expr *>>; $$->emplace_back(state->makeCurPos(@1), $2); }
   | STR DOLLAR_CURLY expr '}' {
       $$ = new std::vector<std::pair<PosIdx, Expr *>>;
-      $$->emplace_back(data->makeCurPos(@1), new ExprString(std::string($1)));
-      $$->emplace_back(data->makeCurPos(@2), $3);
+      $$->emplace_back(state->makeCurPos(@1), new ExprString(std::string($1)));
+      $$->emplace_back(state->makeCurPos(@2), $3);
     }
   ;
 
 path_start
   : PATH {
-    Path path(absPath({$1.p, $1.l}, data->basePath.path.abs()));
+    Path path(absPath({$1.p, $1.l}, state->basePath.path.abs()));
     /* add back in the trailing '/' to the first segment */
     if ($1.p[$1.l-1] == '/' && $1.l > 1)
       path += "/";
-    $$ = new ExprPath(ref<InputAccessor>(data->state.rootFS), std::move(path));
+    $$ = new ExprPath(ref<InputAccessor>(state->state.rootFS), std::move(path));
   }
   | HPATH {
     if (evalSettings.pureEval) {
@@ -552,24 +281,24 @@ path_start
         );
     }
     Path path(getHome() + std::string($1.p + 1, $1.l - 1));
-    $$ = new ExprPath(ref<InputAccessor>(data->state.rootFS), std::move(path));
+    $$ = new ExprPath(ref<InputAccessor>(state->state.rootFS), std::move(path));
   }
   ;
 
 ind_string_parts
-  : ind_string_parts IND_STR { $$ = $1; $1->emplace_back(data->makeCurPos(@2), $2); }
-  | ind_string_parts DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(data->makeCurPos(@2), $3); }
+  : ind_string_parts IND_STR { $$ = $1; $1->emplace_back(state->makeCurPos(@2), $2); }
+  | ind_string_parts DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(state->makeCurPos(@2), $3); }
   | { $$ = new std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>>; }
   ;
 
 binds
-  : binds attrpath '=' expr ';' { $$ = $1; data->addAttr($$, std::move(*$2), $4, data->makeCurPos(@2)); delete $2; }
+  : binds attrpath '=' expr ';' { $$ = $1; state->addAttr($$, std::move(*$2), $4, state->makeCurPos(@2)); delete $2; }
   | binds INHERIT attrs ';'
     { $$ = $1;
       for (auto & i : *$3) {
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
-              data->dupAttr(i.symbol, data->makeCurPos(@3), $$->attrs[i.symbol].pos);
-          auto pos = data->makeCurPos(@3);
+              state->dupAttr(i.symbol, state->makeCurPos(@3), $$->attrs[i.symbol].pos);
+          auto pos = state->makeCurPos(@3);
           $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprVar(CUR_POS, i.symbol), pos, true));
       }
       delete $3;
@@ -579,48 +308,48 @@ binds
       /* !!! Should ensure sharing of the expression in $4. */
       for (auto & i : *$6) {
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
-              data->dupAttr(i.symbol, data->makeCurPos(@6), $$->attrs[i.symbol].pos);
-          $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprSelect(CUR_POS, $4, i.symbol), data->makeCurPos(@6)));
+              state->dupAttr(i.symbol, state->makeCurPos(@6), $$->attrs[i.symbol].pos);
+          $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprSelect(CUR_POS, $4, i.symbol), state->makeCurPos(@6)));
       }
       delete $6;
     }
-  | { $$ = new ExprAttrs(data->makeCurPos(@0)); }
+  | { $$ = new ExprAttrs(state->makeCurPos(@0)); }
   ;
 
 attrs
-  : attrs attr { $$ = $1; $1->push_back(AttrName(data->symbols.create($2))); }
+  : attrs attr { $$ = $1; $1->push_back(AttrName(state->symbols.create($2))); }
   | attrs string_attr
     { $$ = $1;
       ExprString * str = dynamic_cast<ExprString *>($2);
       if (str) {
-          $$->push_back(AttrName(data->symbols.create(str->s)));
+          $$->push_back(AttrName(state->symbols.create(str->s)));
           delete str;
       } else
           throw ParseError({
               .msg = hintfmt("dynamic attributes not allowed in inherit"),
-              .errPos = data->state.positions[data->makeCurPos(@2)]
+              .errPos = state->state.positions[state->makeCurPos(@2)]
           });
     }
   | { $$ = new AttrPath; }
   ;
 
 attrpath
-  : attrpath '.' attr { $$ = $1; $1->push_back(AttrName(data->symbols.create($3))); }
+  : attrpath '.' attr { $$ = $1; $1->push_back(AttrName(state->symbols.create($3))); }
   | attrpath '.' string_attr
     { $$ = $1;
       ExprString * str = dynamic_cast<ExprString *>($3);
       if (str) {
-          $$->push_back(AttrName(data->symbols.create(str->s)));
+          $$->push_back(AttrName(state->symbols.create(str->s)));
           delete str;
       } else
           $$->push_back(AttrName($3));
     }
-  | attr { $$ = new std::vector<AttrName>; $$->push_back(AttrName(data->symbols.create($1))); }
+  | attr { $$ = new std::vector<AttrName>; $$->push_back(AttrName(state->symbols.create($1))); }
   | string_attr
     { $$ = new std::vector<AttrName>;
       ExprString *str = dynamic_cast<ExprString *>($1);
       if (str) {
-          $$->push_back(AttrName(data->symbols.create(str->s)));
+          $$->push_back(AttrName(state->symbols.create(str->s)));
           delete str;
       } else
           $$->push_back(AttrName($1));
@@ -654,8 +383,8 @@ formals
   ;
 
 formal
-  : ID { $$ = new Formal{CUR_POS, data->symbols.create($1), 0}; }
-  | ID '?' expr { $$ = new Formal{CUR_POS, data->symbols.create($1), $3}; }
+  : ID { $$ = new Formal{CUR_POS, state->symbols.create($1), 0}; }
+  | ID '?' expr { $$ = new Formal{CUR_POS, state->symbols.create($1), $3}; }
   ;
 
 %%
@@ -687,7 +416,7 @@ Expr * EvalState::parse(
     std::shared_ptr<StaticEnv> & staticEnv)
 {
     yyscan_t scanner;
-    ParseData data {
+    ParserState state {
         .state = *this,
         .symbols = symbols,
         .basePath = basePath,
@@ -698,11 +427,11 @@ Expr * EvalState::parse(
     Finally _destroy([&] { yylex_destroy(scanner); });
 
     yy_scan_buffer(text, length, scanner);
-    yyparse(scanner, &data);
+    yyparse(scanner, &state);
 
-    data.result->bindVars(*this, staticEnv);
+    state.result->bindVars(*this, staticEnv);
 
-    return data.result;
+    return state.result;
 }