From b5c3e7c499ddbb2674a3a7298f376efa48432ab2 Mon Sep 17 00:00:00 2001
From: dos-reis <gdr@axiomatics.org>
Date: Fri, 7 Dec 2007 01:18:09 +0000
Subject: 	* syntax.spad (Syntax): Add explicit conversion functions from
 	Syntax to Integer, DoubleFloat, Symbol, and String.

---
 src/algebra/syntax.spad | 36 ++++++++++++++++++++++++++++++++----
 1 file changed, 32 insertions(+), 4 deletions(-)

(limited to 'src/algebra/syntax.spad')

diff --git a/src/algebra/syntax.spad b/src/algebra/syntax.spad
index 4962975c..80bee21e 100644
--- a/src/algebra/syntax.spad
+++ b/src/algebra/syntax.spad
@@ -54,16 +54,28 @@ Syntax(): Public == Private where
       ++ e.g. a sequence of cons cell ending with nil.
 
     coerce: Integer -> %
-      ++ convert(i) injects the integer value `i' into the syntax domain
+      ++ coerce(i) injects the integer value `i' into the Syntax domain
+
+    convert: % -> Integer
+      ++ coerce(i) extracts the integer value `i' from the Syntax domain
 
     coerce: DoubleFloat -> %
-      ++ convert(f) injects the float value `f' into the syntax domain
+      ++ coerce(f) injects the float value `f' into the Syntax domain
+
+    convert: % -> DoubleFloat
+      ++ convert(f) extracts the float value `f' from the Syntax domain
 
     coerce: Symbol -> %
-      ++ convert(s) injects the symbol `s' into the syntax domain.
+      ++ coerce(s) injects the symbol `s' into the Syntax domain.
+
+    convert: % -> Symbol
+      ++ convert(s) extracts the symbol `s' from the Syntax domain.
 
     coerce: String -> %
-      ++ convert(s) injects the string value `s' into the syntax domain
+      ++ coerce(s) injects the string value `s' into the syntax domain
+
+    convert: % -> String
+      ++ convert(s) extract the string value `s' from the syntax domain
 
     buildSyntax: (Symbol, List %) -> %
       ++ buildSyntax(op, [a1, ..., an]) builds a syntax object for op(a1,...,an).
@@ -101,15 +113,31 @@ Syntax(): Public == Private where
     coerce(i: Integer): % ==
       i pretend %
 
+    convert(i: %): Integer ==
+      not integer? rep i => userError "invalid conversion target type"
+      i pretend Integer
+
     coerce(f: DoubleFloat): % ==
       f pretend %
 
+    convert(f: %): DoubleFloat ==
+      not float? rep f => userError "invalid conversion target type"
+      f pretend DoubleFloat
+
     coerce(s: Symbol): % ==
       s pretend %
 
+    convert(s: %): Symbol ==
+      not symbol? rep s => userError "invalid conversion target type"
+      s pretend Symbol
+
     coerce(s: String): % ==
       s pretend %
 
+    convert(s: %): String ==
+      not string? rep s => userError "invalid conversion target type"
+      s pretend String
+
     buildSyntax(s: Symbol, l: List %): % ==
       -- ??? ideally we should have overloaded operator `per' that convert
       -- from list of syntax to syntax.  But the compiler is at the 
-- 
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