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Parse and set builtin constraints. First cut.

    We only support one constraint, it must be builtin, and the current
    test case fails to compile in the backend.

--- a/parse/gram.y

+++ b/parse/gram.y

@@ -20,6 +20,7 @@

 static Node *mkpseudodecl(Type *t);

 static void installucons(Stab *st, Type *t);

 Stab *curscope;

+static void constrainwith(Type *t, char *str);

 %}

@@ -120,6 +121,7 @@

 %type <ty> type structdef uniondef tupledef compoundtype functype funcsig

 %type <ty> generictype

 %type <tylist> tuptybody

+%type <node> typaramlist

 %type <tok> asnop cmpop addop mulop shiftop

@@ -274,10 +276,18 @@

         ;

 generictype

-        : Ttyparam {$$ = mktyparam($1->line, $1->str);}

-        /* FIXME: allow constrained typarmas */

+        : Ttyparam typaramlist 

+            {$$ = mktyparam($1->line, $1->str);

+            /* FIXME: this will only work for builtin cstrs */

+             if ($2)

+                constrainwith($$, $2->name.name);}

         ;

+typaramlist

+        : /* empty */ {$$ = NULL;}

+        | Ttrait name {$$ = $2;}

+        ;

+

 compoundtype

         : functype   {$$ = $1;}

         | type Tosqbrac Tcomma Tcsqbrac {$$ = mktyslice($2->line, $1);}

@@ -313,7 +323,7 @@

         ;

 tuptybody

-        : type 

+        : type

             {$$.types = NULL; $$.ntypes = 0;

              lappend(&$$.types, &$$.ntypes, $1);}

         | tuptybody Tcomma type

@@ -355,10 +365,10 @@

         ;

 unionelt /* nb: the ucon union type gets filled in when we have context */

-        : Ttick Tident type Tendln

-            {$$ = mkucon($2->line, mkname($2->line, $2->str), NULL, $3);}

-        | Ttick Tident Tendln

-            {$$ = mkucon($2->line, mkname($2->line, $2->str), NULL, NULL);}

+        : Ttick name type Tendln

+            {$$ = mkucon($2->line, $2, NULL, $3);}

+        | Ttick name Tendln

+            {$$ = mkucon($2->line, $2, NULL, NULL);}

         | visdef Tendln

             {$$ = NULL;}

         | Tendln

@@ -421,10 +431,10 @@

 cmpop   : Teq | Tgt | Tlt | Tge | Tle | Tne ;

 unionexpr

-        : Ttick Tident borexpr

-            {$$ = mkexpr($1->line, Ocons, mkname($2->line, $2->str), $3, NULL);}

-        | Ttick Tident

-            {$$ = mkexpr($1->line, Ocons, mkname($2->line, $2->str), NULL);}

+        : Ttick name borexpr

+            {$$ = mkexpr($1->line, Ocons, $2, $3, NULL);}

+        | Ttick name

+            {$$ = mkexpr($1->line, Ocons, $2, NULL);}

         | borexpr

         ;

@@ -665,6 +675,19 @@

         ;

 %%

+

+static void constrainwith(Type *t, char *str)

+{

+    size_t i;

+

+    for (i = 0; i < ncstrs; i++) {

+        if (!strcmp(cstrtab[i]->name, str)) {

+            setcstr(t, cstrtab[i]);

+            return;

+        }

+    }

+    fatal(t->line, "Constraint %s does not exist", str);

+}

 static Node *mkpseudodecl(Type *t)

 {

--- a/parse/parse.h

+++ b/parse/parse.h

@@ -94,6 +94,8 @@

     int line;

     int resolved;     /* Have we resolved the subtypes? Idempotent, but slow to repeat. */

     Bitset *cstrs;    /* the type constraints matched on this type */

+    Node **cstrlist;  /* The names of the constraints on the type. Used to resolve/fill the bitset */

+    size_t ncstrlist; /* The length of the constraint list above */

     size_t nsub;      /* For compound types */

     size_t nmemb;     /* for aggregate types (struct, union) */

     Type **sub;       /* sub-types; shared by all composite types */

@@ -244,9 +246,9 @@

 extern int line;        /* the last line number we tokenized */

 extern Node *file;      /* the current file we're compiling */

 extern Type **tytab;    /* type -> type map used by inference. size maintained by type creation code */

-extern int ntypes;

+extern size_t ntypes;

 extern Cstr **cstrtab;  /* int -> cstr map */

-extern int ncstrs;

+extern size_t ncstrs;

 extern int maxnid;      /* the maximum node id generated so far */

 extern int maxdid;      /* the maximum decl id generated so far */

--- a/parse/type.c

+++ b/parse/type.c

@@ -18,9 +18,9 @@

 };

 Type **tytab = NULL;

-int ntypes;

+size_t ntypes;

 Cstr **cstrtab;

-int ncstrs;

+size_t ncstrs;

 static Cstr *tycstrs[Ntypes + 1][4];

@@ -271,10 +271,10 @@

 static int cstrfmt(char *buf, size_t len, Type *t)

 {

+    size_t i;

     char *p;

     char *end;

     char *sep;

-    int i;

     if (!t->cstrs || !bscount(t->cstrs))

         return 0;

--- a/test/cstr-builtin.myr

+++ b/test/cstr-builtin.myr

@@ -1,4 +1,4 @@

-const max = {a:@a::tcnum, b:@a::tcnum

+generic max = {a:@a::tcnum, b:@a::tcnum

 	if a > b

 		-> a

 	else